The Biomechanical Behavior of Selected Achilles Tendon Revision Constructs: An Exploratory Cadaveric Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript studies an important topic, because biomechanical evidence for revision Achilles tendon repair is limited. The subject is clinically relevant and potentially useful. However, the current study design is too weak to support strong conclusions.

1) My main concern is that each construct was tested only once, without replication. Also, the specimens showed clear differences in tendon geometry, including cross sectional area and length. Therefore, it is not possible to know if the observed differences are because of the repair technique or simply specimen variability. The authors also state that no statistical comparison was performed, which is appropriate, but then some parts of the manuscript still sound too comparative.

2) Another important issue is the lack of methodological detail. The manuscript should explain more clearly how the cross sectional area was measured, how load to failure testing was performed, what loading rate was used, and how the tendon was fixed during testing. These details are necessary for reproducibility.

3)I also found an important inconsistency. The paper states that four cadaveric lower limbs were used, but five revision strategies were evaluated. This point is confusing and must be clarified clearly in the Methods.

4) Their discussion is partly balanced, because the authors acknowledge the exploratory nature and limitations of the work. Still, the conclusion should be softened more. The statement that the PTT augmented construct had the greatest resistance is descriptively true in this series, but it should not be interpreted as superiority, since only one sample per technique was tested. 

In summary, the manuscript has some value as a pilot or exploratory cadaveric study, but the present version has major methodological limitations. I recommend major revision. The authors should reduce the strength of their claims, clarify the specimen number issue, and improve the methodological description in much more detail. 

Comments on the Quality of English Language

the English should be edited carefully in revision.

Author Response

1. My main concern is that each construct was tested only once, without replication. Also, the specimens showed clear differences in tendon geometry, including cross sectional area and length. Therefore, it is not possible to know if the observed differences are because of the repair technique or simply specimen variability. The authors also state that no statistical comparison was performed, which is appropriate, but then some parts of the manuscript still sound too comparative.

 

Answer: We thank the reviewer for this important observation. We fully agree that the absence of construct replication and the variability in tendon geometry limit the ability to attribute differences in mechanical behavior to the repair technique itself.

The present study was intentionally designed as an exploratory, hypothesis-generating investigation rather than a comparative or inferential analysis. Each construct was evaluated in a single cadaveric specimen to characterize distinct biomechanical behaviors under standardized conditions, not to establish superiority between techniques.

We acknowledge that specimen-specific factors, including cross-sectional area and tendon length, may have influenced the observed results. This limitation has now been emphasized more clearly in the Methods, Results, and Discussion sections.

To address the reviewer’s concern regarding the comparative tone, we have revised the manuscript to remove or soften any statements implying direct comparison or superiority between constructs. All findings are now presented strictly as descriptive observations within individual constructs.

We agree that future studies with larger sample sizes and replication of each construct are necessary to allow statistical comparison and to isolate the effect of repair technique from specimen variability.

The following changes were made in the manuscript:

Methods section: “Each construct was tested in a single specimen without replication. This approach was intentionally adopted to allow the inclusion of multiple distinct revision strategies within a limited cadaveric sample. Accordingly, the study was designed as an exploratory, descriptive analysis, and not for statistical comparison or inference.”

Results section: We have replaced “PTT had the highest load to failure”

With “The highest load to failure observed in this series occurred in the PTT-augmented construct”

 

Discussions section: “Given the absence of replication, differences between constructs must be interpreted as specimen-specific observations rather than technique-dependent effects.”

Conclusion section:

We have removed “had the greatest resistance” with “demonstrated the highest load to failure within this limited experimental series” and “These findings do not imply superiority of any construct.”

 

 

2. Another important issue is the lack of methodological detail. The manuscript should explain more clearly how the cross sectional area was measured, how load to failure testing was performed, what loading rate was used, and how the tendon was fixed during testing. These details are necessary for reproducibility.

We thank the reviewer for highlighting the need for greater methodological clarity. We agree that detailed reporting of biomechanical testing procedures is essential for reproducibility. In the revised manuscript, we have expanded the Methods section to provide a more precise description of Cross-sectional area measurement, the load-to-failure protocol, the applied loading rate during tensile testingand the fixation method of both the calcaneus and proximal tendon during testing. These additions have been incorporated to improve transparency and allow reproducibility of the experimental setup.

The following changes were made in the Methods section:

Cross-sectional area was calculated by measuring tendon width and thickness at the repair site using a digital caliper (precision ±0.1 mm). Measurements were obtained in a standardized region at the midpoint of the repair, and cross-sectional area was approximated assuming an elliptical geometry.

 

The calcaneus was rigidly fixed using a 4-mm Kirschner wire inserted transversely and secured to the testing frame to prevent rotation or displacement. The proximal tendon was clamped using a custom serrated grip connected to the dynamometer, ensuring uniform load distribution and minimizing slippage during testing.

 

Following stress-relaxation testing, uniaxial tensile loading was applied until construct failure. Failure was defined as either complete rupture of the tendon or suture, or a sudden drop (>10%) in recorded force.

 

Load-to-failure testing was performed at a constant displacement rate of 20 mm/min, consistent with previously reported cadaveric tendon biomechanical studies.

During stress-relaxation testing, displacement was held constant once the target load of 100 N was reached, and the decline in force over time was recorded.

 

3. I also found an important inconsistency. The paper states that four cadaveric lower limbs were used, but five revision strategies were evaluated. This point is confusing and must be clarified clearly in the Methods.

We thank the reviewer for pointing out this lack of clarity. We agree that the description of specimen allocation was insufficient and could lead to confusion. Four cadaveric lower limbs were used in this study; however, five revision constructs were evaluated. This was achieved by performing two different repair techniques on separate segments of a single specimen in a sequential manner after completion of the initial mechanical test. No construct was tested more than once, and each repair was performed on a distinct tendon segment.

We acknowledge that this approach may introduce specimen-specific variability and potential bias, and this limitation has now been explicitly stated in the Methods and Discussion sections. The study was designed as an exploratory investigation to characterize different biomechanical behaviors rather than to provide direct comparisons between techniques.The Methods section has been revised to clarify this aspect of the experimental design.

The following changes were made in the Methods section:

Four cadaveric lower limbs were available for testing. To allow evaluation of five distinct revision constructs within this exploratory design, one specimen was used sequentially for two different repair techniques, that is tensioned cross Bunnel followed by Kracow. The second repair was performed on a separate tendon segment after completion of the initial test. Each construct was therefore tested only once, and no direct comparisons between constructs were intended.

 

4. Their discussion is partly balanced, because the authors acknowledge the exploratory nature and limitations of the work. Still, the conclusion should be softened more. The statement that the PTT augmented construct had the greatest resistance is descriptively true in this series, but it should not be interpreted as superiority, since only one sample per technique was tested.

We thank the reviewer for this important comment and agree that the conclusions should reflect the exploratory nature of the study more clearly. In the revised manuscript, we have softened the language in both the Discussion and Conclusion sections to avoid any implication of superiority between constructs. Statements suggesting comparative advantage have been replaced with purely descriptive formulations.

In particular, the statement regarding the PTT-augmented construct has been revised to indicate that it demonstrated the highest load to failure within this limited experimental series, without implying general superiority over other techniques. We have also further emphasized that the findings are preliminary, descriptive, and hypothesis-generating, and should not be interpreted as guidance for clinical decision-making. These revisions have been made to ensure that the conclusions are fully aligned with the study design and its limitations.

The following changes were made in the Conclusion section:

We have replaced „exhibited the greatest resistance to tensile loading” with “demonstrated the highest load to failure within this experimental series”

 

We have added the “These findings do not imply superiority of any construct and should be interpreted strictly within the limitations of this exploratory cadaveric model.”

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript addresses a clinically relevant topic; however, there are several important methodological issues that limit the validity and interpretation of the results. In its current form, the study remains largely descriptive and does not allow for meaningful biomechanical comparison between constructs. On the positive side, the use of cadaveric material is a clear strength and adds value to the work.

A major concern is the lack of information regarding specimen hydration during testing. The authors report only ambient conditions, but do not describe any method of maintaining tissue moisture. This is problematic, as tendon mechanical and viscoelastic properties are highly sensitive to hydration and may be significantly affected.

Another key limitation is that each technique was tested on a single specimen. This precludes any statistical analysis and makes comparisons between constructs unreliable. In addition, the large variability in cross-sectional area introduces bias when interpreting load-based results.

The loading protocol is also limited. The absence of cyclic loading and gap formation assessment reduces the clinical relevance of the findings, particularly in the context of early postoperative conditions.

The literature review appears relatively limited given the long-standing research interest in Achilles tendon biomechanics. It would benefit from expansion and better positioning within the existing body of work.

The conclusions should also be toned down, as the current interpretation goes beyond what can be supported by the exploratory design.

There are also several methodological details missing, including information on specimen handling (e.g., thawing time), and overall transparency could be improved.

Finally, the figures require revision. In Fig. 5, discrete data points from a single specimen are connected with continuous lines, which suggests a deterministic relationship and is potentially misleading. The data should either be presented as individual points or approximated using an appropriate fitted model, rather than directly connecting raw measurements.

Overall, the manuscript would benefit from clearer methodological reporting, improved data presentation, and a more cautious interpretation of the results.

Comments on the Quality of English Language

The manuscript would benefit from professional English language editing. Several sentences are stylistically awkward or lack clarity, and overall readability could be improved. A thorough revision by a native speaker or professional editing service is recommended.

Author Response

1. A major concern is the lack of information regarding specimen hydration during testing. The authors report only ambient conditions, but do not describe any method of maintaining tissue moisture. This is problematic, as tendon mechanical and viscoelastic properties are highly sensitive to hydration and may be significantly affected.

Answer: We thank the reviewer for this important observation. We agree that tendon hydration plays a critical role in preserving viscoelastic and mechanical properties during ex vivo testing. In the present study, specimens were periodically moistened with isotonic saline solution throughout preparation and mechanical testing to minimize dehydration. We acknowledge that continuous hydration control (e.g., immersion or humidity chamber) was not implemented, which represents a methodological limitation. This point has now been clarified in the Methods section and addressed in the Limitations paragraph of the Discussion.

In the Methods section we have added: “Throughout specimen preparation and mechanical testing, tendon surfaces were periodically moistened with isotonic saline solution to reduce dehydration and preserve tissue viscoelastic properties; however, continuous hydration control (e.g., immersion or environmental chamber) was not employed.”

In the Discussion section we have added: “In addition, although specimens were intermittently moistened with saline during testing, strict hydration control was not maintained, and dehydration may have influenced the measured viscoelastic and mechanical properties.”

 

2. Another key limitation is that each technique was tested on a single specimen. This precludes any statistical analysis and makes comparisons between constructs unreliable. In addition, the large variability in cross-sectional area introduces bias when interpreting load-based results.

Answer: We thank the reviewer for this important observation. We fully agree that the absence of construct replication and the variability in tendon geometry limit the ability to attribute differences in mechanical behavior to the repair technique itself.

The present study was intentionally designed as an exploratory, hypothesis-generating investigation rather than a comparative or inferential analysis. Each construct was evaluated in a single cadaveric specimen to characterize distinct biomechanical behaviors under standardized conditions, not to establish superiority between techniques.

We acknowledge that specimen-specific factors, including cross-sectional area and tendon length, may have influenced the observed results. This limitation has now been emphasized more clearly in the Methods, Results, and Discussion sections.

To address the reviewer’s concern regarding the comparative tone, we have revised the manuscript to remove or soften any statements implying direct comparison or superiority between constructs. All findings are now presented strictly as descriptive observations within individual constructs.

We agree that future studies with larger sample sizes and replication of each construct are necessary to allow statistical comparison and to isolate the effect of repair technique from specimen variability.

The following changes were made in the manuscript:

Methods section: “Each construct was tested in a single specimen without replication. This approach was intentionally adopted to allow the inclusion of multiple distinct revision strategies within a limited cadaveric sample. Accordingly, the study was designed as an exploratory, descriptive analysis, and not for statistical comparison or inference.”

Results section: We have replaced “PTT had the highest load to failure”

With “The highest load to failure observed in this series occurred in the PTT-augmented construct”

Discussions section: “Given the absence of replication, differences between constructs must be interpreted as specimen-specific observations rather than technique-dependent effects.”

Conclusion section:

We have removed “had the greatest resistance” with “demonstrated the highest load to failure within this limited experimental series” and “These findings do not imply superiority of any construct.”

 

3. The loading protocol is also limited. The absence of cyclic loading and gap formation assessment reduces the clinical relevance of the findings, particularly in the context of early postoperative conditions.

Answer: We thank the reviewer for this valuable comment. We agree that cyclic loading and gap formation assessment are highly relevant for simulating early postoperative conditions and evaluating construct durability under repetitive stress. In the present study, the mechanical protocol was intentionally limited to time-zero stress-relaxation and load-to-failure testing in order to provide a controlled, descriptive characterization of construct behavior within an exploratory design and limited specimen availability. We acknowledge that the absence of cyclic loading and gap formation analysis reduces the direct clinical applicability of the findings. This limitation has now been further clarified in both the Methods and Discussion sections, and its implications for clinical interpretation have been explicitly addressed.

In the Methods section we have added: „A cyclic loading protocol was not included in the present study; therefore, the mechanical evaluation was limited to time-zero stress-relaxation behavior under constant load and subsequent load-to-failure testing. Consequently, parameters relevant to early postoperative conditions, such as gap formation, cumulative elongation, and fatigue resistance under repetitive loading, were not assessed.”

In the Discussion section we have added: “An additional limitation is the absence of cyclic loading and direct assessment of gap formation to simulate early rehabilitation conditions. These parameters are clinically relevant, as repetitive submaximal loading may lead to progressive elongation, gap formation at the repair site, and eventual construct failure, particularly in the early postoperative period. Their absence limits the ability of the present model to predict construct performance under functional rehabilitation conditions.”

 

4. The literature review appears relatively limited given the long-standing research interest in Achilles tendon biomechanics. It would benefit from expansion and better positioning within the existing body of work.

Answer: We thank the reviewer for this insightful comment. We agree that the Introduction can be strengthened by a broader integration of existing biomechanical literature on Achilles tendon repair. In response, we have expanded the literature review to better contextualize our study within prior biomechanical investigations, particularly those addressing suture techniques, loading protocols, and failure mechanisms in Achilles tendon repair. We have also clarified how the present study differs from existing work by focusing specifically on revision constructs rather than primary repairs and by emphasizing descriptive, time-zero mechanical behavior. These additions improve the positioning of our study within the current body of knowledge.

In the Introduction chapter we added: „A substantial body of biomechanical literature has investigated primary Achilles tendon repair techniques, including comparisons of suture configurations, materials, and fixation strategies under both cyclic and load-to-failure conditions. These studies have demonstrated that suture technique, pretensioning, and construct geometry significantly influence stiffness, gap formation, and ultimate failure strength. In particular, locking configurations such as the Krakow and Bunnell techniques have been shown to provide improved load distribution compared with non-locking repairs, while high-strength suture materials and tape constructs may further enhance mechanical performance under cyclic loading. However, most of these investigations have focused on acute midsubstance ruptures in controlled experimental settings and have relied on replicated constructs with statistical comparison. In contrast, biomechanical data addressing revision-specific conditions—characterized by segmental defects, altered tissue quality, and the need for augmentation or lengthening procedures—remain limited”. We have also added „While prior biomechanical studies have predominantly focused on primary Achilles tendon repair using standardized and replicated constructs, the scientific novelty of this study lies in its focus on revision scenarios, the inclusion of heterogeneous construct types tested under identical conditions, and the evaluation of both viscoelastic behavior and failure modes in a revision-oriented model.”

5. The conclusions should also be toned down, as the current interpretation goes beyond what can be supported by the exploratory design.

Answer: We thank the reviewer for this important comment and agree that the conclusions should reflect the exploratory nature of the study more clearly. In the revised manuscript, we have softened the language in both the Discussion and Conclusion sections to avoid any implication of superiority between constructs. Statements suggesting comparative advantage have been replaced with purely descriptive formulations.

These revisions have been made to ensure that the conclusions are fully aligned with the study design and its limitations.

The following changes were made in the Conclusion section:

We have replaced „exhibited the greatest resistance to tensile loading” with “demonstrated the highest load to failure within this experimental series”

We have added the “These findings do not imply superiority of any construct and should be interpreted strictly within the limitations of this exploratory cadaveric model.”

 

6. There are also several methodological details missing, including information on specimen handling (e.g., thawing time), and overall transparency could be improved.

Answer: We thank the reviewer for this important observation. We agree that detailed reporting of specimen handling is essential for reproducibility and transparency in cadaveric biomechanical studies. In the present study, specimens were thawed at room temperature for a standardized period prior to preparation and testing. We acknowledge that this detail was insufficiently described in the original manuscript. We have now clarified the thawing protocol and expanded the methodological description to improve transparency and reproducibility.

In the Materials section we have added „Prior to testing, specimens were thawed at room temperature for approximately 12 hours to allow complete soft tissue equilibration before preparation and mechanical testing.”. We have also added „Prior to testing, specimens were thawed at room temperature for approximately 12 hours to allow complete soft tissue equilibration before preparation and mechanical testing.” and “All specimens underwent a single freeze–thaw cycle prior to testing.”

 

7. Finally, the figures require revision. In Fig. 5, discrete data points from a single specimen are connected with continuous lines, which suggests a deterministic relationship and is potentially misleading. The data should either be presented as individual points or approximated using an appropriate fitted model, rather than directly connecting raw measurements.

Answer: We thank the reviewer for this important observation. We have changed the image as indicated. 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

This cadaveric study compares five Achilles tendon revision constructs, finding augmented repairs (PTT+Bunnell) highest load-to-failure (235.7 N) and suture-tendon failure in non-augmented techniques.
Major revision required – the study lacks specimen replication (n=1 per construct), no statistical analysis, and insufficient mechanical testing detail.

1. What is the clear objective, scientific novelty, and practical significance of this work given the very small sample size and lack of construct replication?

2. Why were no histological or tissue quality assessments performed to explain how your solution might improve surgical technique beyond raw biomechanics?

3. Could you discuss potential cellular or biological effects of the augmentation techniques on tendon healing, not just mechanical behavior?

4. How do your findings directly compare with existing clinical practices or prior biomechanical studies on revision Achilles repair?

5. Have you considered applying new biomaterials (e.g., 10.3390/jfb14050259) or additive manufacturing approaches to enhance construct performance?

6. Can you present full elastic modulus graphs and more detailed physical-mechanical properties to support your conclusions, as this is a technical engineering-oriented journal?

7. The conclusions lack specific numerical thresholds (e.g., safe load limits, stiffness values) – please add concrete figures for clinical/engineering translation.

8. How would the viscoelastic behavior change under cyclic loading simulating early rehabilitation, not just a single stress-relaxation test at 100 N?

9. Could the failure mode shift again if a different suture material (e.g., tape vs. FiberWire) or pretension protocol was used in these revision constructs?

10. What minimum cross-sectional area or tissue quality index would you recommend to avoid suture-tendon interface failure based on your exploratory data?

11. The authors need to update the reference list with publications from 2021–2026, comprising at least 85% of the total references, and increase the total number of citations to a minimum of 30. Additionally, there are no citations to the journal itself or to MDPI journal groups.

Author Response

1. What is the clear objective, scientific novelty, and practical significance of this work given the very small sample size and lack of construct replication?

Response:
We thank the reviewer for this important comment. We agree that the small sample size and absence of construct replication limit the generalizability and preclude statistical comparison. However, the study was intentionally designed as an exploratory biomechanical investigation aimed at addressing a gap in the current literature.

To clarify this, we have revised the manuscript to explicitly state the objective, scientific novelty and practica significance.

We have clarified throughout the manuscript that the results are descriptive and exploratory, not intended to establish superiority, and we have strengthened statements in the Abstract, Introduction, and Discussion accordingly.

In the abstract we have replaced “The purpose is to evaluate viscoelastic behavior…” with “The objective of this exploratory study was to provide a descriptive biomechanical characterization of commonly used Achilles tendon revision constructs, focusing on viscoelastic behavior, load-to-failure properties, and failure mechanisms under standardized loading conditions.” We have also added “Although limited by the absence of construct replication, this study provides hypothesis-generating biomechanical insight into failure mechanisms of revision constructs, which may inform future comparative studies and surgical strategy selection.”

 

In the Introduction section, we have rewritten a paraghaph accordingly:

“Despite the wide range of available revision techniques, biomechanical data comparing their mechanical behavior under standardized loading conditions remain scarce, particularly in revision-specific settings.

The objective of the present study was therefore to provide a descriptive, exploratory biomechanical characterizationof commonly used Achilles tendon revision constructs.

The scientific novelty of this study lies in its focus on revision scenarios rather than primary repair, the inclusion of heterogeneous construct types tested under identical conditions, and the evaluation of both viscoelastic behavior and failure modes, which remain insufficiently described in the current literature.

This study was not designed to establish comparative superiority, but to generate mechanistic insights and hypotheses to guide future biomechanical and clinical investigations.”

In the Methods section, we have replaced “Each construct was evaluated in a single specimen…” with “Each construct was tested in a single specimen without replication. This approach was intentionally adopted to allow the inclusion of multiple distinct revision strategies within a limited cadaveric sample. Accordingly, the study was designed as an exploratory, descriptive analysis, and not for statistical comparison or inference.”

 

In the Discussion section we have added the following: “The primary contribution of this study is not comparative evaluation but mechanistic characterization of revision constructs under controlled loading conditions. Given the limited biomechanical evidence available for revision Achilles tendon surgery, particularly regarding failure modes and viscoelastic behavior, this exploratory approach provides preliminary insights that may guide hypothesis generation and future study design.”

 

In the Conclusion section, we have added “While not generalizable, these findings highlight construct-specific mechanical vulnerabilities that may be relevant when selecting revision strategies in the context of compromised tendon quality.”

 

 

 

 

 

2. Why were no histological or tissue quality assessments performed to explain how your solution might improve surgical technique beyond raw biomechanics?

Response: We thank the reviewer for this valuable comment. We agree that histological and tissue quality assessments could provide important complementary information regarding tendon structure and healing potential. However, the primary aim of this study was to perform a controlled biomechanical evaluation of revision constructs, and the experimental design was intentionally limited to mechanical testing. The study was designed as an exploratory biomechanical investigation focusing on construct behavior under standardized loading conditions. The inclusion of histological analysis would have required a fundamentally different experimental framework, including tissue processing protocols and outcome measures not directly aligned with the mechanical endpoints evaluated here.

 

In the Methods section we have added: “No histological or microstructural analysis was performed, as the study was designed to evaluate time-zero mechanical properties under controlled loading conditions rather than biological tissue response.”

 

In the Discussions sectin we have added: “Another limitation of this study is the absence of histological or tissue quality assessment. While such analyses could provide insight into tendon microstructure and degeneration, the use of fresh-frozen cadaveric specimens primarily allows evaluation of time-zero mechanical behavior rather than biological healing. Moreover, mechanical testing to failure compromises tissue integrity, limiting the feasibility and interpretability of subsequent histological analysis. Therefore, the present findings should be interpreted as purely biomechanical, without direct correlation to tissue remodeling or healing capacity.”

 

“Future studies combining biomechanical testing with histological analysis or in vivo models may provide a more comprehensive understanding of how construct mechanics interact with tendon biology and healing processes.”

 

 

 

 

 

 

 

 

3. Could you discuss potential cellular or biological effects of the augmentation techniques on tendon healing, not just mechanical behavior?

Response: We thank the reviewer for this insightful suggestion. We agree that augmentation techniques may influence not only the mechanical properties of the repair but also the biological environment and tendon healing response.

As the present study was designed as a time-zero cadaveric biomechanical investigation, it does not allow direct evaluation of cellular or biological processes. However, we have revised the Discussion section to incorporate a focused consideration of the potential biological implications of augmentation techniques, based on existing literature.

We have added this paragraph to the Discussion section: “Beyond their mechanical role, augmentation techniques may also influence the biological environment of tendon healing. Although this cadaveric model does not permit direct assessment of cellular or histological processes, several potential mechanisms can be considered. Tendon graft augmentation may act as a scaffold facilitating cellular infiltration, neovascularization, and extracellular matrix remodeling. In addition, by increasing the cross-sectional area and redistributing load across the repair site, augmented constructs may reduce local strain concentrations, potentially promoting a more favorable biological healing response. Conversely, increased construct stiffness and bulk may alter physiological stress distribution and mechanotransduction, with uncertain effects on long-term tendon remodeling. The use of autologous grafts, such as posterior tibial tendon, may further contribute to biological integration through viable tissue incorporation. However, these effects remain theoretical in the context of the present time-zero biomechanical study and should be investigated in future in vivo or histological studies.”

 

 

4. How do your findings directly compare with existing clinical practices or prior biomechanical studies on revision Achilles repair?

Response: We thank the reviewer for this important comment. We agree that the relationship between our findings, current clinical practice, and prior biomechanical literature should be made more explicit.

In the revised manuscript, we clarified that current clinical practice in revision Achilles repair remains highly individualized, with construct selection generally based on defect size, residual tissue quality, and surgeon experience rather than on a standardized biomechanical evidence base. In this context, our findings are not intended to challenge established clinical algorithms, but rather to provide time-zero mechanical data that may help interpret the strengths and vulnerabilities of several commonly used revision strategies.

We also strengthened the comparison with prior biomechanical studies. Most published biomechanical investigations have focused on primary Achilles tendon repair techniques, whereas revision-specific biomechanical data remain limited. Our results are broadly consistent with prior work showing that suture configuration and pretension influence construct stiffness and failure behavior, and that augmented constructs can shift failure away from the suture–tendon interface. At the same time, unlike prior replicated biomechanical studies, our exploratory design evaluated different revision constructs in single specimens, so our findings should be interpreted as descriptive and hypothesis-generating rather than as evidence of comparative superiority.

We have therefore revised the Discussion to better position our results relative to both current revision practice and previously published biomechanical studies, while emphasizing the limits of direct comparison due to differences in model design, construct selection, and replication methodology.

In the Discussion section we have added: “The present findings should be interpreted in the context of current clinical practice for revision Achilles tendon rupture, which remains largely individualized. In routine practice, revision strategy is typically selected according to tendon gap size, residual tissue quality, prior surgery, and surgeon preference, with augmentation, tendon transfer, or advancement procedures used when direct end-to-end repair is not feasible. Our results do not establish superiority of any technique, but provide time-zero biomechanical observations that may help explain why augmented constructs may better tolerate tensile loading, whereas non-augmented repairs may remain limited by the suture–tendon interface.”

We have rewritten a paragraph accordingly: “Load-to-failure testing revealed the highest ultimate load in the PTT-augmented Bunnell construct, which failed at the tendon substance rather than the suture–tendon interface. In contrast, both the Krakow and Tensioned cross-lock Bunnell repairs failed at the level of the suture. These findings are broadly consistent with prior biomechanical studies showing that construct configuration and pretension influence repair stiffness and failure mode, and that stronger or augmented constructs may shift the weakest point away from the repair site. Compared with previously published studies reporting higher failure loads for the Tensioned cross-lock Bunnell technique, the lower failure force observed in the present study may be explained by the revision-like defect model, compromised local tissue conditions, and localized stress concentration at the transverse suture segment, which may have acted as a focal cutting element rather than a load-distributing structure.”

 

We have added a new paragraph to the Discussion section: “Direct comparison with prior biomechanical literature must be made cautiously. Most available cadaveric studies have evaluated primary midsubstance Achilles repairs using replicated constructs and averaged failure values, whereas the present study focused on revision-oriented techniques in a non-replicated exploratory model. Accordingly, our findings are more useful for identifying construct-specific mechanical patterns and failure mechanisms than for quantitative ranking against previously published techniques. This distinction is particularly relevant because revision surgery involves poorer tissue quality, segmental loss, and reconstructive strategies that are not fully represented in primary repair models.”

 

We have added in the Conclusion section: “In relation to existing clinical practice, these findings support the view that augmentation may be mechanically advantageous in revision settings with compromised tissue quality, although no definitive treatment recommendations can be made from this exploratory model.”

 

5. Have you considered applying new biomaterials (e.g., 10.3390/jfb14050259) or additive manufacturing approaches to enhance construct performance?

Response: We thank the reviewer for this valuable and forward-looking suggestion. We agree that emerging biomaterials and additive manufacturing approaches represent promising avenues for improving tendon repair constructs.

The primary objective of the present study, however, was to provide a baseline biomechanical characterization of commonly used, clinically established revision techniques under standardized conditions. For this reason, we deliberately focused on widely accessible surgical constructs using conventional high-strength sutures and autologous tissue augmentation, allowing direct relevance to current clinical practice.

We have now expanded the Discussion section to acknowledge the potential role of advanced biomaterials and additive manufacturing strategies, including bioengineered scaffolds, synthetic augmentation materials, and patient-specific constructs. These approaches may enhance tendon repair by improving load distribution, providing biologically active scaffolds, and enabling customized structural reinforcement.

At the same time, we note that such technologies remain largely experimental in the context of Achilles tendon revision, with limited standardized biomechanical data and unclear clinical translation. We therefore consider the present study as establishing a reference framework of time-zero mechanical behavior against which future biomaterial-augmented or additively manufactured constructs may be evaluated. We have incorporated these considerations into the revised manuscript and highlighted this area as an important direction for future research.

We have added the following paragraph in the Discussion section: “Emerging strategies in tendon repair, including the use of advanced biomaterials and additive manufacturing techniques, may further enhance the mechanical and biological performance of revision constructs. Bioengineered scaffolds, synthetic augmentation materials, and three-dimensional printed structures have the potential to improve load distribution, provide a template for cellular infiltration, and allow patient-specific construct design. Such approaches may address some of the limitations of conventional suture-based repairs, particularly in cases of extensive tissue loss or poor tendon quality. However, these technologies remain largely experimental in the context of Achilles tendon revision, and standardized biomechanical and clinical data are currently limited. The present findings may therefore serve as a baseline for comparison in future studies evaluating biomaterial-augmented or additively manufactured repair strategies.”

 

6. Can you present full elastic modulus graphs and more detailed physical-mechanical properties to support your conclusions, as this is a technical engineering-oriented journal?

Response: We thank the reviewer for this important suggestion and agree that a more detailed presentation of mechanical data would enhance the technical clarity of the manuscript.

In the present study, mechanical parameters including ultimate tensile strength, strain at failure, and Young’s moduluswere calculated and are reported in Table 3. However, due to the exploratory design and lack of construct replication, the dataset does not support robust curve-based analysis (e.g., averaged stress–strain curves or comparative elastic modulus plots), which are typically required for meaningful graphical representation in engineering-oriented studies.

Additionally, each construct was tested in a single specimen with heterogeneous geometry and material properties, which limits the interpretability of full stress–strain curves as representative material behavior. Presenting individual curves could be misleading, as observed differences may reflect specimen variability rather than construct-dependent mechanical properties.

To address the reviewer’s comment, we have clarified in the Methods how mechanical parameters (including Young’s modulus) were derived; we have ensured consistent reporting of physical-mechanical properties across all constructs; we have emphasized in the Discussion that the reported values are descriptive and not intended for comparative material characterization.

We agree that future studies with replicated constructs and standardized geometry would allow the generation of full stress–strain curves and more advanced mechanical analysis, including elastic modulus profiling.

We have added the following paragraph to the Methds section: “Young’s modulus was estimated from the linear region of the load–displacement curve, normalized to cross-sectional area and initial length. Given the exploratory design and specimen heterogeneity, these values are reported descriptively and do not represent intrinsic material properties.”

 

We have added the following paragraph to the Results section: “Due to the absence of construct replication and variability in specimen geometry, full stress–strain curves are not presented, and mechanical parameters are reported as single-measure descriptors for each construct.”

 

We have added the following paragraph to the Discussions section: “The study does not include full stress–strain curve analysis or elastic modulus profiling. Because each construct was tested in a single specimen with variable geometry, the calculated mechanical parameters should be interpreted as construct-specific descriptors rather than intrinsic material properties. Future studies with replicated samples would allow more rigorous mechanical characterization, including curve-based analysis.”

 

 

 

7. The conclusions lack specific numerical thresholds (e.g., safe load limits, stiffness values) – please add concrete figures for clinical/engineering translation.

Response: We thank the reviewer for this valuable suggestion and agree that quantitative thresholds would enhance clinical and engineering interpretability.

However, due to the exploratory design, absence of construct replication, and specimen-specific variability in geometry and material properties, the present dataset does not support the definition of reliable numerical thresholds such as “safe load limits” or stiffness cut-off values. The reported mechanical values represent single-measure observations for each construct rather than statistically robust estimates, and translating them into clinical thresholds could be misleading.

To address the reviewer’s concern while maintaining scientific rigor, we have revised the manuscript toexplicitly report key numerical values (e.g., load-to-failure ranges, displacement, and Young’s modulus) within the text of the Results and Conclusions; provide contextual interpretation of these values, particularly in relation to early postoperative loading conditions; and clarify that these values should be interpreted as descriptive reference points rather than prescriptive thresholds.

We now highlight, for example, that augmented constructs demonstrated failure loads exceeding 200 N in this experimental setup, whereas some non-augmented constructs failed below 100 N, indicating substantial variability in initial mechanical resistance.

We emphasize that defining clinically relevant safe loading thresholds would require larger, replicated biomechanical studies and in vivo correlation, which are beyond the scope of the present work.

In the Results section we added: “In this experimental series, load-to-failure values ranged from 47.5 N to 235.7 N across constructs. Augmented repairs exceeded 200 N, whereas certain non-augmented and advancement-based constructs failed below 100 N, reflecting substantial variability in initial mechanical resistance.”

 

In the Discussions section we added: “Although the present study was not designed to define clinical thresholds, the observed range of failure loads provides a descriptive indication of construct behavior under tensile loading. Constructs failing below 100 N may be more susceptible to early mechanical compromise under tensile stress, whereas those exceeding 200 N demonstrated greater resistance in this time-zero setting. However, these values should not be interpreted as safe loading limits, as in vivo forces and biological healing responses are not replicated in this model.”

 

In the Conclusion section we added: In this series, failure loads ranged from approximately 50 N to over 230 N, with augmented constructs demonstrating the highest resistance to tensile loading.”

 

8. How would the viscoelastic behavior change under cyclic loading simulating early rehabilitation, not just a single stress-relaxation test at 100 N?

Response: We thank the reviewer for this important comment. We agree that cyclic loading protocols would provide a more clinically relevant simulation of early rehabilitation than a single stress-relaxation test.

The present study was designed as an exploratory time-zero biomechanical evaluation, with emphasis on initial viscoelastic response, load-to-failure behavior, and failure mode under standardized conditions. For this reason, we used a constant-load stress-relaxation test at 100 N to characterize short-term viscoelastic behavior in a controlled and reproducible manner. We acknowledge, however, that this protocol does not replicate the repetitive submaximal loading that occurs during early postoperative mobilization.

Under cyclic loading, it is likely that the constructs would demonstrate additional features such as progressive elongation, cumulative gap formation, reduction in stiffness, and earlier failure in constructs with weaker suture–tendon interfaces. Augmented constructs might be expected to better distribute repeated loads and delay catastrophic failure, whereas more compliant constructs could exhibit greater cyclic creep. However, these effects cannot be determined directly from the present dataset and should therefore be regarded as hypothesis-based rather than demonstrated findings.

We have revised the manuscript to explicitly acknowledge this limitation and to identify cyclic loading as an essential direction for future research, particularly for evaluating construct performance under rehabilitation-relevant conditions.

We have added the following paragraph in the Methods section: “A cyclic loading protocol was not included in the present study; therefore, the mechanical evaluation was limited to time-zero stress-relaxation behavior under constant load and subsequent load-to-failure testing.”

 

We have added the following paragraph in the Discussions section: “The present viscoelastic findings should be interpreted within the limits of a single constant-load protocol. In a more rehabilitation-relevant cyclic loading model, constructs would likely exhibit additional time-dependent phenomena such as cumulative elongation, gap formation, progressive stiffness loss, and fatigue-related failure. Repairs limited by the suture–tendon interface may be particularly vulnerable to repeated loading, whereas augmented constructs may provide improved load sharing and delayed structural failure. At the same time, more compliant augmented constructs could also demonstrate greater cyclic creep. Because these responses were not directly tested in the current study, such implications remain speculative and should be examined in future cyclic loading experiments.”

 

We have added the following paragraph in the Discussions section: “An additional limitation is the absence of cyclic loading to simulate early rehabilitation. The stress-relaxation test at 100 N provides only a simplified assessment of short-term viscoelastic response and does not reproduce repetitive postoperative loading. Future studies should incorporate cyclic loading protocols to assess gap formation, creep behavior, and fatigue resistance under clinically relevant rehabilitation conditions.”

 

 

9. Could the failure mode shift again if a different suture material (e.g., tape vs. FiberWire) or pretension protocol was used in these revision constructs?

Response: We thank the reviewer for this important comment. We agree that both suture material and pretension protocol could influence not only the absolute mechanical performance of the constructs but also the observed failure mode.

In the present study, all repairs were performed with the same No. 2 FiberWire and by a single surgeon in order to reduce technical variability and isolate the effect of construct configuration as much as possible. However, prior biomechanical literature suggests that broader high-strength tape constructs may improve load distribution and reduce focal stress concentration at the tendon–suture interface compared with round sutures, while suture pretension has also been shown to affect repair stiffness and gap behavior. Therefore, it is plausible that the use of tape rather than FiberWire, or a different pretensioning approach, could shift failure away from suture cut-through and modify the balance between stiffness, elongation, and tendon-level rupture.

At the same time, such effects would likely be construct-specific. In repairs that failed primarily at the suture–tendon interface in our study, alternative materials or pretension protocols might reduce localized cutting and delay suture-related failure. Conversely, increasing construct stiffness through different materials or greater pretension might also transfer stresses to the tendon substance or augmentation segment, potentially producing a different failure pattern.

Because the present study did not vary suture material or pretension systematically, these possibilities remain speculative. We have revised the Discussion to acknowledge this point and to identify suture material and pretension as important variables for future revision-specific biomechanical studies.

In the Methods section, after the sentence “All repairs were performed using No. 2 FiberWire by the same surgeon to reduce technical variability.” We have added “Accordingly, the effects of alternative suture materials or different pretensioning protocols were not evaluated in the present study.”

 

In the Discussions chapter we have added “The observed failure modes may also depend on variables not directly tested in the present study, particularly suture material and pretension protocol. Prior biomechanical studies have shown that high-strength tape constructs may improve load distribution compared with round sutures, while pretensioning can modify construct stiffness and gap resistance. In this context, repairs that failed at the suture–tendon interface in the present series might exhibit a different failure pattern if broader tape-like sutures or alternative pretensioning strategies were used, potentially reducing localized cut-through. Conversely, increased stiffness or reduced elongation could also shift the weak point toward the tendon substance or augmentation segment. Because these variables were controlled rather than compared in the current experimental design, such effects remain hypothetical and warrant dedicated investigation.”

 

 

 

• What minimum cross-sectional area or tissue quality index would you recommend to avoid suture-tendon interface failure based on your exploratory data?

Response: We thank the reviewer for this important question. However, based on the present exploratory dataset, we do not consider it scientifically justified to recommend a minimum cross-sectional area or tissue quality index to avoid suture–tendon interface failure.

In this study, each construct was tested in a single specimen, with substantial heterogeneity in tendon geometry, repair configuration, and augmentation strategy. Although constructs with smaller cross-sectional areas in our series tended to fail at the suture–tendon interface, the study design does not allow separation of the independent effects of cross-sectional area, intrinsic tissue quality, and suture configuration. In addition, no histological or quantitative tissue quality assessment was performed, so a tissue quality index cannot be derived from the present data.

We have therefore revised the manuscript to clarify that the observed association between smaller or non-augmented constructs and suture-related failure is descriptive only and should not be interpreted as a basis for a clinical threshold. At most, our findings suggest that reduced tendon bulk and lack of augmentation may be associated with greater vulnerability to interface failure in a time-zero setting, but defining a minimum safe cross-sectional area would require replicated studies with standardized geometry and direct tissue quality assessment.

In the Discussions section we have added: “Although smaller cross-sectional areas in the present series were associated with suture–tendon interface failure in some non-augmented repairs, the exploratory design does not permit identification of a minimum geometric threshold for safe fixation. Cross-sectional area, tissue quality, augmentation, and suture configuration are interdependent in this model and cannot be analyzed separately.”

We have added the following limitation “The study does not support definition of a minimum cross-sectional area or tissue quality index predictive of suture–tendon interface failure. No histological or quantitative tissue quality assessment was performed, and the lack of construct replication precludes threshold analysis.”

 

We have added future-direction in the Discussions section: “Future studies should evaluate larger replicated cohorts with standardized repair constructs and direct tissue quality assessment to determine whether geometric or structural thresholds can predict interface failure.”

 

• The authors need to update the reference list with publications from 2021–2026, comprising at least 85% of the total references, and increase the total number of citations to a minimum of 30. Additionally, there are no citations to the journal itself or to MDPI journal groups.

Response: We thank the reviewer for this suggestion. The reference list has been revised to incorporate recent publications (2021–2026), and the total number of citations has been increased accordingly to 35. References were selected based on their scientific relevance to the topic. We included additional relevant references from MDPI journals and the journal itself.

Author Response File: Author Response.docx

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript entitled “Biomechanical Behavior of Selected Achilles Tendon Revision Constructs: An Exploratory Cadaveric Study” presents an experimental evaluation of several surgical techniques for Achilles tendon revision using a cadaveric model. The topic is clinically relevant, as rerupture after Achilles tendon repair remains a challenging complication associated with significant functional impairment. The study attempts to address an important gap in biomechanical evidence guiding revision strategies.

- The authors focus exclusively on revision constructs. While this is justified by the clinical problem of rerupture, the Introduction would benefit from a clearer distinction between primary and revision repair strategies. A brief overview of current consensus on primary Achilles tendon repair techniques should be included, along with an explanation of how revision scenarios differ biomechanically and clinically. This is particularly important given that “donors had no known history of lower-limb surgery”, which limits the ability of the model to fully replicate true revision conditions.

- The manuscript states that indications for revision surgery include “persistent gapping,” but this term is not defined.

- The statement that mechanical parameters were calculated based on cross-sectional area measurements requires clarification. Since the Achilles tendon has a non-uniform geometry, the authors should specify the exact location of measurement, the method used, and whether measurements were standardized across specimens.

- There is an inconsistency in the reported sample size. The Methods section mentions four cadaveric lower limbs, while five constructs were evaluated. In addition, Figure 2 and Table 1 appear to include five samples. This discrepancy should be clarified, and the experimental design described more explicitly.

- The reported load-to-failure values appear substantially lower than expected. For example, the highest value (235 N for PTT augmentation with Bunnell repair) corresponds to approximately 23.5 kg of force, much less that the body weight, whereas the native Achilles tendon is known to withstand loads up to several thousands N under physiological conditions. The authors should discuss this discrepancy, clarify whether the results reflect early postoperative construct strength rather than native tendon properties, and relate their findings to previously published biomechanical data.

Figure 4 should be replaced with a digital version, as a photograph of handwritten material is not appropriate for publication.

The Abstract is structured using numbered sections (1) Background, (2) Methods, etc., which appears unconventional and should be reformatted according to the journal guidelines. In addition, there is an apparent typographical error (“5”) in the middle of the Abstract that should be corrected.

Author Response

1. The authors focus exclusively on revision constructs. While this is justified by the clinical problem of rerupture, the Introduction would benefit from a clearer distinction between primary and revision repair strategies. A brief overview of current consensus on primary Achilles tendon repair techniques should be included, along with an explanation of how revision scenarios differ biomechanically and clinically. This is particularly important given that “donors had no known history of lower-limb surgery”, which limits the ability of the model to fully replicate true revision conditions.

 

Response: We thank the reviewer for this insightful comment. We agree that a clearer distinction between primary and revision Achilles tendon repair strategies would strengthen the Introduction.

In response, we have revised the Introduction to address the comment above.

„ In primary Achilles tendon rupture, surgical repair strategies typically aim to restore tendon continuity while preserving vascularity and minimizing soft tissue disruption. Commonly used techniques include open end-to-end repairs such as the Krakow or Bunnell configurations, as well as minimally invasive and percutaneous approaches, which have gained popularity due to reduced wound complications while maintaining comparable rerupture rates. Current consensus suggests that no single technique has demonstrated clear superiority, and choice of repair is often guided by surgeon preference and patient-specific factors, including activity level and tendon quality.

In contrast, revision Achilles tendon repair presents distinct biomechanical and clinical challenges. Rerupture is frequently associated with compromised tendon integrity, scar formation, elongation, and segmental defects, which impair the ability of standard end-to-end repairs to restore native load transmission. As a result, revision strategies often require augmentation procedures, tendon transfers, or lengthening techniques to bridge defects and improve construct strength. These approaches alter both the geometry and mechanical behavior of the tendon, particularly with respect to stiffness, load distribution, and failure mechanisms.

It should also be noted that, although the present study aimed to simulate revision conditions through segmental tendon excision, the cadaveric specimens had no prior surgical intervention. Consequently, the model does not fully replicate the biological environment of true revision cases, where altered vascularity, adhesions, and degenerative changes may further influence mechanical behavior.”

 

2. The manuscript states that indications for revision surgery include “persistent gapping,” but this term is not defined.

 

Response: We thank the reviewer for highlighting this point. We agree that the term “persistent gapping” requires clarification to avoid ambiguity.

In response, we have revised the manuscript to include a clear definition of persistent gapping in the context of Achilles tendon repair. Specifically, persistent gapping refers to a measurable separation between the tendon ends following primary repair, typically identified on clinical examination or imaging (e.g., ultrasound or MRI), which may occur either immediately postoperatively or during early rehabilitation due to insufficient construct strength or elongation under load. Clinically relevant gapping is often considered when separation exceeds approximately 5–10 mm, as this has been associated with impaired tendon healing, elongation, and suboptimal functional outcomes.

This clarification has been added to the Introduction to improve precision and reader understanding.

We have replaced the sentece “Indications for revision surgery include tendon rerupture, persistent gapping, and failure of wound or soft-tissue healing[7].” with “Indications for revision surgery include tendon rerupture, persistent gapping—defined as a clinically or radiologically detectable separation between tendon ends (typically >5–10 mm) following primary repair due to elongation or mechanical insufficiency—and failure of wound or soft-tissue healing[7].”

 

3. The statement that mechanical parameters were calculated based on cross-sectional area measurements requires clarification. Since the Achilles tendon has a non-uniform geometry, the authors should specify the exact location of measurement, the method used, and whether measurements were standardized across specimens.

 

Response: We thank the reviewer for this important observation. We agree that clarification regarding cross-sectional area (CSA) measurements is necessary, particularly given the non-uniform geometry of the Achilles tendon.

In response, we have revised the Methods section to explicitly describe the location of CSA measurement, the measurement technique used, and the standardization approach across specimens.

Briefly, CSA was measured at the level of the repair site following completion of each construct, using caliper-based measurements of tendon width and thickness, from which CSA was calculated assuming an elliptical profile. All measurements were performed in a standardized manner by the same investigator to reduce variability. We also acknowledge that this approach represents an approximation and may not fully capture the complex geometry of the tendon, which is now stated as a methodological limitation.

We have added in the Methods section: „Cross-sectional area (CSA) measurements were obtained at the level of the repair site for each construct following completion of the suturing technique. Tendon width and thickness were measured using a digital caliper, and CSA was calculated assuming an elliptical geometry using the formula π × (width/2) × (thickness/2). All measurements were performed in a standardized fashion by the same investigator to minimize interobserver variability. Given the non-uniform morphology of the Achilles tendon, this method provides an approximation of the local cross-sectional area at the repair site and may not fully capture regional variations in tendon geometry.”

 

4. There is an inconsistency in the reported sample size. The Methods section mentions four cadaveric lower limbs, while five constructs were evaluated. In addition, Figure 2 and Table 1 appear to include five samples. This discrepancy should be clarified, and the experimental design described more explicitly.

Response: We thank the reviewer for pointing out this lack of clarity. We agree that the description of specimen allocation was insufficient and could lead to confusion. Four cadaveric lower limbs were used in this study; however, five revision constructs were evaluated. This was achieved by performing two different repair techniques on separate segments of a single specimen in a sequential manner after completion of the initial mechanical test. No construct was tested more than once, and each repair was performed on a distinct tendon segment.

We acknowledge that this approach may introduce specimen-specific variability and potential bias, and this limitation has now been explicitly stated in the Methods and Discussion sections. The study was designed as an exploratory investigation to characterize different biomechanical behaviors rather than to provide direct comparisons between techniques.The Methods section has been revised to clarify this aspect of the experimental design.

The following changes were made in the Methods section: „Four cadaveric lower limbs were available for testing. To allow evaluation of five distinct revision constructs within this exploratory design, one specimen was used sequentially for two different repair techniques, that is tensioned cross Bunnel followed by Kracow. The second repair was performed on a separate tendon segment after completion of the initial test. Each construct was therefore tested only once, and no direct comparisons between constructs were intended.”

 

5. The reported load-to-failure values appear substantially lower than expected. For example, the highest value (235 N for PTT augmentation with Bunnell repair) corresponds to approximately 23.5 kg of force, much less that the body weight, whereas the native Achilles tendon is known to withstand loads up to several thousands N under physiological conditions. The authors should discuss this discrepancy, clarify whether the results reflect early postoperative construct strength rather than native tendon properties, and relate their findings to previously published biomechanical data.

Response: We thank the reviewer for this important and valid observation. We agree that the reported load-to-failure values are substantially lower than the known strength of the native Achilles tendon and that this distinction requires clearer explanation.

In response, we have revised the Discussion to clarify that the measured values reflect the initial mechanical strength of repair constructs at time zero, rather than the intrinsic strength of the intact Achilles tendon. The experimental model evaluates the suture–tendon construct as the weakest link, which is known to fail at significantly lower loads compared to native tendon tissue.

In the Discussion section we added „The load-to-failure values observed in the present study are substantially lower than the forces sustained by the native Achilles tendon under physiological conditions, which have been reported to reach several thousand newtons during activities such as walking or running. This discrepancy reflects the fundamental difference between intact tendon properties and the mechanical behavior of repair constructs at time zero. In the immediate postoperative setting, the strength of the repair is governed primarily by the suture–tendon interface and fixation technique, which represent the weakest link in the construct.

Previous cadaveric studies evaluating primary Achilles tendon repairs have reported load-to-failure values typically ranging between approximately 100 and 400 N, depending on suture configuration, material, and testing protocol. In this context, the values observed in the present study—particularly for non-augmented repairs—are consistent with existing biomechanical literature. The higher load observed in the posterior tibial tendon–augmented construct may reflect improved load sharing and increased cross-sectional area, although this was accompanied by altered compliance characteristics.

Importantly, the present results should be interpreted as representing early postoperative construct strength prior to biological healing. In vivo, progressive tendon healing and remodeling contribute substantially to the restoration of mechanical integrity over time. In revision settings, where tissue quality is compromised and defects are present, initial construct strength may be further reduced, reinforcing the importance of protected loading during early rehabilitation.”

 

6. Figure 4 should be replaced with a digital version, as a photograph of handwritten material is not appropriate for publication.

We have realized a digital version of image 4.

 

7. The Abstract is structured using numbered sections (1) Background, (2) Methods, etc., which appears unconventional and should be reformatted according to the journal guidelines. In addition, there is an apparent typographical error (“5”) in the middle of the Abstract that should be corrected.

Response: We thank the reviewer for this comment. The abstract has been reformatted to remove the numbered section headings and now follows the journal’s recommended structure without headings. Additionally, we corrected the apparent typographical error (“5”) in the middle of the Abstract.

Author Response File: Author Response.docx

Reviewer 5 Report

Comments and Suggestions for Authors

 

1. How do the characteristics of the Achilles tendon from frozen cadavers compare to those from living individuals?
2. “A custom mechanical testing apparatus was used to apply uniaxial tensile loading. The 100-N constant load and 240-second duration were selected to represent submaximal early postoperative tensile forces and to allow assessment of short-term viscoelastic behavior, consistent with prior cadaveric tendon studies.” What type of tensile testing machine was used in this paper?
3. Figure 4 is unclear. The article's explanation of Figure 4 is not detailed enough.
4. “The purpose is to evaluate viscoelastic behavior, load-to-failure characteristics, and failure modes of frequently used Achilles tendon revision techniques in a cadaveric model”. The entire paper makes no discussion or conclusion regarding viscoelasticity.

Comments on the Quality of English Language

The English writing must be improved.

Author Response

 

1. How do the characteristics of the Achilles tendon from frozen cadavers compare to those from living individuals?

 

Response: Thank you for your suggestion. The following statement has been added to the Discussion section.

 

Fresh-frozen grafts have limitations compared to those of living tissue including: lack of neuromuscular intercation and absence of biological activity. Nevertheless, according to Moon et al. (2006) and Arnout et al. (2013), the refreezing of specimens has little or no effect on the biomechanical properties.

 

 

Moon DK, Woo SL-Y, Takakura Y, Gabriel MT, Abramowitch SD. The effects of refreezing on the viscoelastic and tensile properties of ligaments. J Biomech. 2006.

 

Arnout N, Verdonk R, Verdonk P. The influence of freezing on the tensile strength of tendon grafts: A biomechanical study. Acta Orthopaedica Belgica. 2013;79(4):435–443 

 

 

2. “A custom mechanical testing apparatus was used to apply uniaxial tensile loading. The 100-N constant load and 240-second duration were selected to represent submaximal early postoperative tensile forces and to allow assessment of short-term viscoelastic behavior, consistent with prior cadaveric tendon studies.” What type of tensile testing machine was used in this paper?

 

 

Response: Thank you for your suggestion. The following statement has been added to the Discussion section to increase the clarity of our methods.

In the present study, tensile loading was applied using a custom-built uniaxial mechanical testing apparatus, consisting of rigid calcaneal fixation and a dynamometer-based loading system attached to the proximal tendon. The device si similar to the ones used in previous studies such as Swanson et al. And Macaluson et al. This configuration allowed controlled application and continuous recording of tensile force along the anatomical axis of the Achilles tendon.

We acknowledge that, unlike commercially available universal testing systems, the device used in this study was specifically designed for cadaveric testing to accommodate anatomical fixation constraints. Similar custom or adapted loading setups are commonly reported in cadaveric tendon biomechanical studies, where specimen geometry and fixation requirements limit the use of standard testing frames.

Swanson DR, Nazemi A, Macaluso B, Hassan CR, Paulus M, Qin Y-X, Komatsu DE.
Biomechanical Comparison of Krackow Open Repair and Percutaneous Achilles Repair System for Achilles Tendon Rupture: A Cadaveric and Finite Element Model Study.
Stony Brook Medicine Journal of Scholarship, Innovation, and Quality Improvement – Orthopaedics. 2021;15:29–35.

 

Macaluso B, Hassan CR, Swanson DR, et al.
Biomechanical comparison of Krackow repair and percutaneous Achilles repair system for Achilles tendon rupture fixation: A cadaveric and finite element analysis study.
Foot & Ankle Orthopaedics. 2022;7(1):24730114221088502.

 

 

3. Figure 4 is unclear. The article's explanation of Figure 4 is not detailed enough.

 

Thank you for your comment. We have increased the quality of the image and provided a more detailed explanation.

 

 

Figure 4: The pattern of each suture studied in order from left to right.The figure highlights a key technical feature of the V–Y tendon plasty construct: distal to the V–Y advancement, the tendon is folded longitudinally onto itself, creating a doubled tendon segment that is stabilized with three simple sutures before application of the double Kessler repair.

 

4. “The purpose is to evaluate viscoelastic behavior, load-to-failure characteristics, and failure modes of frequently used Achilles tendon revision techniques in a cadaveric model”. The entire paper makes no discussion or conclusion regarding viscoelasticity.

 

Response: Thank you for this important observation. We acknowledge that, although viscoelastic behavior was included as a stated objective of the study, its discussion in the original manuscript was limited and not sufficiently emphasized in the Discussion and Conclusions sections. In the present study, viscoelastic properties were assessed through stress-relaxation testing under a constant 100 N load over 240 seconds, which demonstrated a consistent time-dependent decrease in retained force across all constructs, reflecting the intrinsic viscoelastic behavior of tendon tissue. Notably, differences in residual force and relaxation rate were observed between constructs, with the tensioned cross-lock Bunnell repair maintaining higher residual force over time, while augmented and circumferential constructs exhibited greater relaxation, suggesting increased compliance.

 

We have added  the following to the Discussion section:

All constructs demonstrated a characteristic stress-relaxation pattern, with a rapid decline in retained force within the first 60 seconds followed by a slower phase of relaxation. This biphasic response is consistent with the intrinsic viscoelastic behavior of tendon tissue, reflecting fluid redistribution and internal structural reorganization under sustained load.

Differences in relaxation profiles were observed between constructs. The tensioned cross-lock Bunnell repair maintained higher residual force over time, suggesting reduced early elongation under constant load, whereas augmented and circumferentially reinforced constructs exhibited greater relaxation, indicating increased compliance. From a biomechanical perspective, increased compliance may facilitate load sharing and energy dissipation; however, it may also predispose to early gap formation at the repair site under sustained postoperative loading conditions.

Although the present cadaveric model does not allow direct extrapolation to clinical outcomes, these findings highlight the potential importance of viscoelastic properties in the early postoperative period, where time-dependent elongation may influence construct stability and tendon healing.

We have added  the following to the Conclusion:

 

In addition to differences in load-to-failure characteristics and failure modes, all constructs demonstrated viscoelastic behavior, with distinct stress-relaxation profiles that may influence early mechanical stability under sustained loading conditions.

 

 

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This revised manuscript is improved compared with the previous version. The authors have appropriately clarified that the study is exploratory and descriptive, and they now acknowledge that the absence of construct replication precludes inferential comparison. This is an important and appropriate correction. Methodological details have also been expanded, which improves transparency. However, the fundamental limitation of the study remains unchanged, since each construct was tested only once and one specimen was used sequentially for two repairs. Therefore, the findings should remain strictly descriptive and hypothesis generating. In addition, the manuscript still requires careful language editing and formatting revision, particularly in the discussion and reference section. I believe the manuscript is closer to publishable form, but some further revision is still needed before acceptance.

Comments on the Quality of English Language

the English should be edited carefully in revision.

Author Response

1. However, the fundamental limitation of the study remains unchanged, since each construct was tested only once and one specimen was used sequentially for two repairs. Therefore, the findings should remain strictly descriptive and hypothesis generating.

 

Answer: Thank you for your comment. We have made the following changes in order to address your request.

 

In the Abstract section, we have added: „Given that each construct was tested only once and that one specimen was used sequentially for two repairs, the findings should be interpreted strictly as descriptive and hypothesis-generating, without any basis for comparative or inferential conclusions.

Given that each construct was tested only once and that one specimen was used sequentially for two repairs, the findings should be interpreted strictly as descriptive and hypothesis-generating, without any basis for comparative or inferential conclusions.”

 

In the Materials and Methods section we have added: “Each construct was therefore tested only once, and one specimen was used sequentially for two different repairs. This design precludes any form of replication and introduces potential specimen-dependent effects. Accordingly, no direct comparisons between constructs were intended, and the study was designed strictly as a descriptive, hypothesis-generating analysis.”

 

In the Materials and Methods section we have also added: “Each construct was tested in a single specimen without replication, and one specimen underwent sequential testing of two repair techniques. This approach was intentionally adopted to allow inclusion of multiple constructs within a limited cadaveric sample; however, it represents a fundamental methodological limitation. Accordingly, the results are strictly descriptive and intended only for hypothesis generation, without statistical comparison or inference.”

 

In the Results section we have added: “Due to the absence of construct replication and the use of one specimen for sequential testing of two repairs, all results represent single-measure observations that may be influenced by specimen-specific factors. Accordingly, the findings are reported strictly as descriptive data without any inferential or comparative interpretation.”

 

In the Conclusion section we have added: „Given the absence of construct replication and the sequential use of one specimen, these findings should be interpreted strictly as descriptive and hypothesis-generating, and should not be used to support comparative or clinical conclusions.”

 

 

2. In addition, the manuscript still requires careful language editing and formatting revision, particularly in the discussion and reference section. I believe the manuscript is closer to publishable form, but some further revision is still needed before acceptance.

 

Answer: Thank you for your comment. We have performed the requested Language Editing service from MDPI and we have the modified version.

Reviewer 3 Report

Comments and Suggestions for Authors

Accept in present form

Author Response

We thank the reviewer. 

Reviewer 5 Report

Comments and Suggestions for Authors

1. “A custom mechanical testing apparatus was used to apply uniaxial tensile loading. The 100-N constant load and 240-second duration were selected to represent submaximal early postoperative tensile forces and to allow assessment of short-term viscoelastic behavior, consistent with prior cadaveric tendon studies.” What type of tensile testing machine was used in this paper? Although the author states that the tensile testing machine was developed in the author's laboratory, the author should specify the range of tensile force and tensile speed values ​​for the machine.
2. “The purpose is to evaluate viscoelastic behavior, load-to-failure characteristics, and failure modes of frequently used Achilles tendon revision techniques in a cadaveric model”. The entire paper makes no discussion or conclusion regarding viscoelasticity. The author's explanation is still insufficient; please provide further details.

Comments on the Quality of English Language

The English writing must be improved.

Author Response

1. “A custom mechanical testing apparatus was used to apply uniaxial tensile loading. The 100-N constant load and 240-second duration were selected to represent submaximal early postoperative tensile forces and to allow assessment of short-term viscoelastic behavior, consistent with prior cadaveric tendon studies.” What type of tensile testing machine was used in this paper? Although the author states that the tensile testing machine was developed in the author's laboratory, the author should specify the range of tensile force and tensile speed values ​​for the machine.

 

Answer: Thank you for this important clarification. The mechanical testing device used in this study was a custom-built uniaxial tensile testing apparatus developed for cadaveric tendon testing, consisting of a rigid fixation system and a dynamometer-based force measurement unit.

We agree that additional technical specifications are necessary for reproducibility. We have therefore revised the manuscript to include details regarding the measurable force range, displacement rate (tensile speed), and calibration procedure of the device.

Specifically, the system allowed controlled uniaxial loading within a force range exceeding the maximum loads applied in this study (up to at least 500 N), and tensile loading during load-to-failure testing was performed at a constant displacement rate of 20 mm/min. Force measurements were obtained using a calibrated dynamometer with appropriate sensitivity for low-load tendon testing.

These details have now been added to the Methods section.

“A custom mechanical testing apparatus was used to apply uniaxial tensile loading. The system consisted of a rigid fixation frame with calcaneal anchoring and a dynamometer-based force measurement unit connected to the proximal tendon clamp. The device was designed to allow controlled uniaxial tensile loading within a force range exceeding 500 N, which is above the maximum loads applied in the present study.”

 

“Force measurements were obtained using a calibrated dynamometer with appropriate sensitivity for low-load tendon testing, and system calibration was verified using standardized weights prior to each testing session. Load-to-failure testing was performed at a constant displacement rate of 20 mm/min, within the operational capabilities of the device.”

 

 

1. “The purpose is to evaluate viscoelastic behavior, load-to-failure characteristics, and failure modes of frequently used Achilles tendon revision techniques in a cadaveric model”. The entire paper makes no discussion or conclusion regarding viscoelasticity. The author's explanation is still insufficient; please provide further details.

 

Answer: Thank you for this valuable observation. We agree that although viscoelastic behavior (stress-relaxation) was measured and presented in the Results section, its interpretation and integration into the Discussion and Conclusions were not sufficiently developed in the original manuscript.

To address this, we have expanded the Discussion to provide a more detailed analysis of the observed stress-relaxation patterns, including their biomechanical significance in terms of early construct elongation, load redistribution, and potential implications for postoperative stability.

In particular, we now discuss how differences in residual force and relaxation rates between constructs may reflect variations in compliance, which could influence gap formation and mechanical integrity under sustained loading conditions in the early postoperative period.

Additionally, we have revised the Conclusion section to explicitly incorporate viscoelastic behavior as a key finding of the study.

These revisions ensure that viscoelasticity is not only reported but also interpreted within a clinically relevant biomechanical framework.

In the Discussion section we have added: All constructs demonstrated a characteristic stress-relaxation pattern, reflecting the viscoelastic behavior of tendon tissue. Differences between constructs suggest variation in compliance, with higher residual force indicating reduced early elongation under sustained load. From a biomechanical perspective, increased relaxation may facilitate load distribution but may also predispose to early gap formation at the repair site. Although limited to a constant-load protocol, these findings indicate that viscoelastic properties may influence early construct stability in the postoperative period.

 

In the Conclusion section we have added: “In addition to differences in load-to-failure characteristics and failure modes, all constructs demonstrated viscoelastic behavior, with variations in stress-relaxation that may influence early mechanical stability.”

Round 3

Reviewer 5 Report

Comments and Suggestions for Authors

1. While the author responded with information about tensile testing machines, commercial tensile testing machines are used by numerous international testing teams, thus their stability and test repeatability are highly accurate. How can the author guarantee the quality of their self-developed machine? Furthermore, for self-developed machines, the author should describe the machine's structure and materials, the motor power used for tensile testing, etc., and provide detailed information.

2. “The purpose is to evaluate viscoelastic behavior, load-to-failure characteristics, and failure modes of frequently used Achilles tendon revision techniques in a cadaveric model”. The entire paper makes no discussion or conclusion regarding viscoelasticity. The author's explanation is still insufficient; please provide further details.

Answer: Thank you for this valuable observation. We agree that although viscoelastic behavior (stress-relaxation) was measured and presented in the Results section, its interpretation and integration into the Discussion and Conclusions were not sufficiently developed in the original manuscript.

The author did not respond to the review committee's comments.

Comments on the Quality of English Language

The English writing must be improved.

Author Response

1. While the author responded with information about tensile testing machines, commercial tensile testing machines are used by numerous international testing teams, thus their stability and test repeatability are highly accurate. How can the author guarantee the quality of their self-developed machine? Furthermore, for self-developed machines, the author should describe the machine's structure and materials, the motor power used for tensile testing, etc., and provide detailed information.

 

Response: We thank the reviewer for the comment. We have added supplimentary information as requested in the Materials section and in the Discussion section.

 

Materials section: „A custom mechanical testing apparatus was used to apply uniaxial tensile loading. The device was constructed from four vertically oriented threaded metallic support rods reinforced with rigid oak stabilization plates to minimize deformation during loading. The system consisted of a rigid fixation frame with calcaneal anchoring and a dynamometer-based force measurement unit connected to the proximal tendon clamp. Tensile loading was generated using a custom linear actuator system driven by a NEMA 17 bipolar stepper motor (holding torque approximately 0.36 Nm, 200 steps/revolution) coupled to a lead screw displacement mechanism, allowing controlled displacement-rate tensile testing. The motor-driven actuator mechanism was positioned centrally on the superior plate, allowing gradual and controlled application of tensile force on the dynamometer, respectively on the tendon. The motor–lead screw system was theoretically capable of generating tensile forces exceeding 500 N, which was above the maximum loads applied in the present study.The 100 N constant load and 240-second duration were selected to represent submaximal early postoperative tensile forces and to allow for the assessment of short-term viscoelastic behavior, consistent with prior cadaveric tendon studies. The calcaneus was rigidly fixed using a 4 mm Kirschner wire inserted transversely and secured to the testing frame to prevent rotation or displacement. The proximal tendon was clamped using a custom serrated grip connected to the dynamometer, ensuring uniform load distribution and minimizing slippage during testing. Calibration was performed using standardized weights prior to testing. Repeated calibration cycles performed before testing demonstrated stable and reproducible force measurements throughout the operational loading range. A preload of 10 N was applied, followed by preconditioning with five load–unload cycles at 50 N. Force measurements were obtained using a calibrated dynamometer with appropriate sensitivity for low-load tendon testing, and calibration stability was verified prior to each testing session. Load-to-failure testing was performed at a constant displacement rate of 20 mm/min, within the operational capabilities of the device. All specimens underwent a single freeze–thaw cycle prior to testing.”

 

 

Discussion section: „We acknowledge that commercially available universal testing systems provide highly standardized loading conditions and excellent intertrial repeatability. However, the custom-built apparatus used in the present study was specifically designed for cadaveric Achilles tendon testing in order to accommodate anatomical fixation constraints and minimize specimen slippage during tensile loading. The system incorporated rigid metallic fixation components, displacement-controlled actuator-driven loading, calibrated dynamometer-based force acquisition, and repeated calibration cycles performed prior to testing sessions to ensure stable and reproducible force measurements within the loading range investigated.

Similar custom or adapted loading systems have been reported in previous cadaveric tendon biomechanical studies where specimen geometry and fixation requirements limit the use of standard commercial testing frames [21,22]. Although the present device was not formally validated against a commercial universal testing machine, repeated calibration procedures and controlled loading conditions provided acceptable measurement consistency for exploratory cadaveric biomechanical evaluation. Nevertheless, the absence of formal inter-device validation remains a limitation of the present study and should be addressed in future investigations. Given the absence of replication, differences between constructs must be interpreted as specimen-specific observations rather than technique-dependent effects. Accordingly, comparisons between constructs should be interpreted descriptively and not as evidence of relative biomechanical superiority.”

 

 

2. The purpose is to evaluate viscoelastic behavior, load-to-failure characteristics, and failure modes of frequently used Achilles tendon revision techniques in a cadaveric model”. The entire paper makes no discussion or conclusion regarding viscoelasticity. The author's explanation is still insufficient; please provide further details.

 

Response: We thank the reviewer for this important observation and agree that the discussion of viscoelastic behavior was insufficiently developed in the previous version of the manuscript.

To address this concern, we substantially expanded the interpretation of the stress-relaxation findings throughout the Discussion and Conclusions sections. Specifically, we added a detailed explanation of the biomechanical significance of stress relaxation in tendon repair constructs, including the role of internal load redistribution within the collagen–suture complex under constant elongation conditions. We further discussed how differences in relaxation profiles may reflect variations in construct compliance, early elongation behavior, and potential susceptibility to postoperative gap formation.

In addition, we clarified the clinical relevance of viscoelastic behavior in the early postoperative period and discussed how increased compliance may influence load sharing, energy dissipation, and mechanical stability under sustained loading conditions. We also expanded the limitations section to explain that the present viscoelastic assessment was limited to a constant-load stress-relaxation protocol and did not include cyclic loading or fatigue testing, which may further influence time-dependent mechanical behavior.

Finally, viscoelastic findings were explicitly incorporated into the Conclusions section, where we now state that all tested constructs demonstrated viscoelastic behavior with distinct stress-relaxation profiles that may influence early mechanical stability after revision repair.

 

 

Discussion section: „All constructs demonstrated a characteristic stress relaxation pattern, reflecting the viscoelastic behavior of tendon tissue. Stress relaxation in tendon repair constructs reflects internal redistribution of load within the collagen–suture complex over time, resulting in a gradual decline in retained force despite constant elongation. In sutured constructs, the stress relaxation is influenced by suture configuration, tissue quality, and the mechanical interaction between the thread and the tendon tissue under tensile loading conditions. Differences between constructs suggest variation in compliance, with higher residual force indicating reduced early elongation under sustained load. The tensioned cross-lock Bunnell repair maintained higher residual force over time, whereas augmented and circumferentially reinforced constructs exhibited greater relaxation, indicating increased compliance. From a biomechanical perspective, increased compliance may facilitate load sharing and energy dissipation; however, it may also predispose to early gap formation at the repair site under sustained postoperative loading conditions. Although limited to a constant-load protocol, these findings indicate that viscoelastic properties may influence early construct stability in the postoperative period. These findings suggest that viscoelastic behavior may represent an additional determinant of construct performance beyond load-to-failure characteristics alone.

 

Although the present cadaveric model does not allow for direct extrapolation to clinical outcomes, these findings highlight the potential importance of viscoelastic properties in the early postoperative period, where time-dependent elongation may influence construct stability and tendon healing.”

 

 

Discussion section: „In addition, although specimens were intermittently moistened with saline during testing, strict hydration control was not maintained, and dehydration may have influenced the measured viscoelastic and mechanical properties.”

 

Discussion section: „The present viscoelastic findings should be interpreted within the limits of a single constant-load protocol. In a more rehabilitation-relevant cyclic loading model, constructs would likely exhibit additional time-dependent phenomena such as cumulative elongation, gap formation, progressive stiffness loss, and fatigue-related failure. Repairs limited by the suture–tendon interface may be particularly vulnerable to repeated loading, whereas augmented constructs may provide improved load sharing and delayed structural failure. At the same time, more compliant augmented constructs could also demonstrate greater cyclic creep. Because these responses were not directly tested in the current study, such implications remain speculative and should be examined in future cyclic loading experiments. An additional limitation is the absence of cyclic loading and direct assessment of gap formation to simulate early rehabilitation conditions. These parameters are clinically relevant, as repetitive submaximal loading may lead to progressive elongation, gap formation at the repair site, and eventual construct failure, particularly in the early postoperative period. Their absence limits the ability of the present model to predict construct performance under functional rehabilitation conditions. The stress relaxation test at 100 N provides only a simplified assessment of short-term viscoelastic response and does not reproduce repetitive postoperative loading. Future studies should incorporate cyclic loading protocols to assess gap formation, creep behavior, and fatigue resistance under clinically relevant rehabilitation conditions.”

 

Discussion seection: „The primary contribution of this study is not a comparative evaluation but a mechanistic characterization of revision constructs under controlled loading conditions. Given the limited biomechanical evidence available for revision Achilles tendon surgery, particularly regarding failure modes and viscoelastic behavior, this exploratory approach provides preliminary insights that may guide hypothesis generation and future study design.”

 

 

Conclusion section: „Additionally, the three constructs evaluated under the stress-relaxation test presented viscoelastic behavior, with variations in relaxation profiles, reflecting the time-dependent mechanical behavior of repaired tendon tissue. The construct incorporating V-Y lengthening showed limited mechanical durability under sustained load. These findings underscore the importance of tailoring revision strategies to tissue quality and defect characteristics. In addition to differences in load-to-failure characteristics and failure modes, all constructs demonstrated viscoelastic behavior, with variations in stress relaxation that may influence early mechanical stability.”

 

 

Author Response File: Author Response.docx