Impact of Distal Tibiofibular Joint Anatomy on Reduction Outcome in Dynamic Suture Button Stabilization of the Distal Syndesmosis—A CT Analysis

Round 1

Reviewer 1 Report (Previous Reviewer 1)

Comments and Suggestions for Authors

I thank the authors for their improvements. My concerns have been addressed.

Author Response

Comments 1: I Thank the authors for their improvements. My concerns have been addressed.

Response 1:

Dear Reviewer,

we would like to thank you for processing and editing our article, "Impact of distal tibio-fibular joint anatomy on reduction outcome in dynamic suture button stabilization of the distal syndesmosis - a CT analysis".

We are pleased that we were able to adequately address your concerns.

On behalf of the authors

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

Thank you for the opportunity to review this paper. I like the expression taught to me by a very senior foot and ankle surgeon “There is no such thing as a simple ankle ORIF”. The challenge here is, arguably, we do not really understand what on earth ‘normal’ is. This is especially true when we consider the dynamic nature of the ankle joint. The Distal Tib/Fib Joint is especially difficult to discern what normal is, and this makes research so challenging. There have been previous works on this exact topic which shows great variability of the anatomy, and no clear evidence that on a static CT, with the ankle in ‘god-knows-what’ position that there is any evidence for or against suspensory buttons over screws. Furthermore, which syndesmosis needs to be stabilised is still up for debate, just attend any foot and ankle conference!

 

Line 13: (Actually throughout the paper) Please remove the quotation  marks unless you  refer to whom you are quoting. As this is not a very common phrase, I’d suggest to avoid using apostrophes too. This is term YOU are using to rightly describe the flexible nature of fixation with suture buttons.

 

Line 34: In which groups? Is it necessary to do this for all Weber B’s?

Line 38: Using which method of fixation?

Line 44-47: This is a tough thing to say. There is evidence/authors suggesting the more widespread use of CTs in patients with syndesmotic stabilisation but to say that every patient needs a CT or that this is in fact the “general standard” is a stretch in may countries; I can attest to Sweden, Denmark and Australia on this. You say below that this is controversial (lines 52-54)

 

Line 80: In your hook test, what did you do to assess the sagittal instability? Or when you say syndesmotic injury do you only mean in the coronal plane? What about rotationally or sagittally unstable syndesmosis injury patterns?

 

Line 92: What consideration was given to the relative position of the talus in all these measurements? I.e. the amount of dorsi or plantar flexion?

Line 160: why did you need to use a KW H test? Did you ever have 3 categorical independent groups?

Line 162: Why use Spearman-Rho? As it was used, was the data assumed to be ordinal or continuous?

 

Results generally –

The sentence “there was no significant difference….” Is not requires. Please simple put the effect size with CIs and the p-value (Or whatever is appropriate).

When reporting a SD can you simply use the accepted ‘±’ sign instead?

Please write in past tense ‘was’ not ‘is’

Line 196: what is this p-value representing? The inter-sex difference?

 

Did you consider analysing the tract of the bone tunnels? I aks this because I wonder too if the location of the tunnel may have a slight effect on the resultalnt reduction. I am aware that Arthrex say it is “Self-centring” however I have seen cases that very much contradict this. Especially those with a deficient anterior tubercle

 

Discussion

I accept that the authors show that there is a large variation in the population for the measured outcomes, but am I correct in saying you found almost no difference between the injured and uninjured side? So why CT both?? There are measurements taken that I accept cannot be taken when the fibula is not anatomically reduced, but for those that can be taken, a very good picture of the anatomy can be made in the surgeons mind. Especially when an open reduction of the fibula was performed here….

I simply cannot see why you are suggesting to CT both? What information do you get from the uninjured side routinely? You are doubling the radiation.

If there is evidence in this paper to support bilateral CT, you have not convinced me in the results and discussion and this needs to be made far far far clearer!

Would the authors consider dynamic CT assessment?

Author Response

Comment 1: General consideration.

Response 1: Thank you very much for your valuable comment. We fully share your assessment regarding the complexity of injuries to the distal tibiofibular joint (DTFJ).

Isolated syndesmotic lesions without accompanying ankle fractures were deliberately excluded, as diagnosis and therapeutic stabilization in this constellation remain the subject of intense discussion and research, as you have pointed out.

In our study, we therefore only considered unstable DTFJ injuries that showed clear signs of instability based on the fracture pattern and confirmed intraoperatively.

 

Comment 2: Please remove the quotation marks unless you refer to whom you are quoting. As this is not a very common phrase, I’d suggest to avoid using apostrophes too. This is term YOU are using to rightly describe the flexible nature of fixation with suture buttons.

Response 2: We have reviewed the entire text again and removed all quotation marks that do not refer to a direct quotation.

 

Comment 3: Line 34: In which groups? Is it necessary to do this for all Weber B’s?

Response 3: Thank you for your valuable comment and precise inquiry. We have clarified the relevant paragraph accordingly.

Line 38 – 40: There is a consensus that anatomical reduction and stabilization of a proven unstable distal tibiofibular joint (DTFJ) in course of the operative treatment of unstable ankle fractures is necessary.

Comments 4: Line 38: Using which method of fixation?

Response 4: We have clarified the relevant paragraph accordingly.

Line 42 – 44: It has been demonstrated that malreduction of the DTFJ, particularly in the sagittal plane, occurs in up to 40% of cases after stabilization with a syndesmosis screw (SYS) or suture button system (SBS) [4,5].

 

Comment 5: Line 44-47: This is a tough thing to say. There is evidence/authors suggesting the more widespread use of CTs in patients with syndesmotic stabilisation but to say that every patient needs a CT or that this is in fact the “general standard” is a stretch in may countries; I can attest to Sweden, Denmark and Australia on this. You say below that this is controversial (lines 52-54)

 

Response 5: We appreciate your constructive feedback regarding lines 44-47. We concur with your assertion that routine CT monitoring after syndesmotic stabilization is not universally regarded as the prevailing standard.

Due to the significant interindividual anatomical variations in the distal tibiofibular joint, we consider intra- or post-operative CT control to be a useful procedure for precise reduction assessment. However, we acknowledge that this approach may not be universally applicable in all healthcare systems.

We have therefore revised the relevant paragraph to reflect this change. Instead of offering a universally valid recommendation, we now emphasize that several studies underline the benefits of CT control.

Line 62 -65: Based on these findings, it may be recommended that intra- or postoperative bilateral computed tomography (CT) be performed to precisely evaluate the congruity of the DTFJ following surgical stabilization, both by SYS and by SBS [2,4,11,17,21,22].

 

Comment 6: Line 80: In your hook test, what did you do to assess the sagittal instability? Or when you say syndesmotic injury do you only mean in the coronal plane? What about rotationally or sagittally unstable syndesmosis injury patterns?

Response 6: The paragraph was initially worded too imprecisely. By combining two tests, we aim to address coronal, sagittal, and rotational instabilities, ensuring that only those syndesmoses that are evidently unstable are stabilized. We have revised the relevant section—now on lines 88 through 94—in order to communicate this procedure more clearly.

Line 88 – 94: This was done with the hook test, as recommended by AO for coronal instability [24,26,27]. In this procedure, the distal fibula is grasped with a hook and pulled horizontally towards the lateral side. The foot is fixed by the examiner [28]. Subsequently, the external rotation test was performed to assess sagittal and rotational instability under fluoroscopy [29]. In both tests the beam is aligned perpendicular to the tibia and centered at the joint-line, while the foot is rotated internally by 15-20° while the ankle joint was in neutral position [24].

 

Comment 7: Line 92: What consideration was given to the relative position of the talus in all these measurements? I.e. the amount of dorsi or plantar flexion?

Response 7: Thank you for your inquiry regarding foot position during CT examinations.

All examinations were performed by trained personnel to ensure standardised positioning conditions. Patients were positioned supine with symmetrically fixed and rotated feet (15–20° inward). The ankle joint was in a neutral position (approximately 90° between the longitudinal axis of the tibia and the sole of the foot). This ensured that the influence of varying talus positions on the measured distances was minimized. The patients were positioned supine with their feet fixed symmetrically in a standardized position: feet rotated 15–20° internally and the ankle joints in a neutral position. We have revised the relevant section now on lines 102 through 104.

Line 102 - 104: The patients were positioned supine with their feet fixed symmetrically in a standardized position: feet rotated 15–20° internally with the ankle joints in a neutral position.

 

Comment 8: Line 160: why did you need to use a KW H test? Did you ever have 3 categorical independent groups?

Response 8: The statistical analysis was carried out in collaboration with the statistical institute of our hospital. There were analyses with patients who had a ventral, anatomical and posterior position of the syndesmosis. However, there were no differences.

Comment 9: Line 162: Why use Spearman-Rho? As it was used, was the data assumed to be ordinal or continuous?

Response 9: We appreciate your constructive criticism regarding the selection of correlation method (line 162).

We initially calculated Spearman's ρ to account for the potential non-normal distribution of the measured values. After consulting with our statistics team and re-examining the data, we have determined that the distribution assumptions for a Pearson correlation are sufficiently met.

Therefore, all correlations were recalculated using the Pearson correlation coefficient. A comparison of the Spearman values reported previously indicates only minor deviations, which have no impact on the statistical evaluation or interpretation of the results.

The corresponding changes are documented in Tables 3 and 5.

 

Comments 10 – 12 The sentence “there was no significant difference….” Is not requires. Please simple put the effect size with CIs and the p-value (Or whatever is appropriate).

When reporting a SD can you simply use the accepted ‘±’ sign instead?

Please write in past tense ‘was’ not ‘is’

Response 10 -12: The comments have been incorporated into the manuscript and we thank you again for your helpful suggestions.

Comment 13: Line 196: what is this p-value representing? The inter-sex difference?

Response 13: For better readability of the results, "p > 0.05" was indicated in cases of non-significance. Please refer to Tables 2 and 4 for the individual parameters. There were no differences between the sexes.

Comment 14: Did you consider analysing the tract of the bone tunnels? I ask this because I also wonder if the location of the tunnel may have a slight effect on the resulting reduction. I am aware that Arthrex say it is ‘self-centring,’ however, I have seen cases that very much contradict this. Especially those with a deficient anterior tubercle.

Response 14: In a previous study (“Does the orientation of syndesmosis fixative device affect the immediate reduction of the distal tibiofibular joint?” - https://doi.org/10.1007/s00402-021-04073-x), it was shown that the alignment of the drill channel of the suture button system has no impact on the CT-morphological reduction outcome of the syndesmosis. This was also demonstrated for the syndesmotic screw. In our opinion, the initial reduction and preliminary fixation prior to definitive stabilization are decisive factors in determining whether malreduction or incorrect stabilisation occurs. The aspect of increased malalignment in the absence of the tubercle cannot be adequately addressed in our study, as only anatomically reduced fractures were included. However, a shallow incision (DI = depth of incisura) does not represent a risk factor in malreduction by suture button stabilization.

The impact of malreduced fracture parts on the position of the syndesmosis is the subject of further investigations, which are currently underway.

 

Comment 15 and 16: I accept that the authors show that there is a large variation in the population for the measured outcomes, but am I correct in saying you found almost no difference between the injured and uninjured side? So why CT both?? There are measurements taken that I accept cannot be taken when the fibula is not anatomically reduced, but for those that can be taken, a very good picture of the anatomy can be made in the surgeons mind. Especially when an open reduction of the fibula was performed here….

I simply cannot see why you are suggesting to CT both? What information do you get from the uninjured side routinely? You are doubling the radiation.

Response 15: Thank you for your critical question – it touches on the core of our study design.

The primary objective was to investigate correlations between patient-specific anatomy and the quality of reduction. This was done using a correlation analysis of the respective parameters. Although the mean values of the measured parameters on the native and operative sides differ only slightly, Table 2 shows that the interindividual range of normal values significantly exceeds the clinically accepted side difference of ≈ 2 mm, and that malreductions > 2 mm also occurred within the cohort. Without reciprocal CT, it would not be possible to clearly distinguish whether a deviation is a genuine malalignment or merely anatomical variance.

This fact was discussed in detail with our radiologists and medical physicists, as the justifiable indication must be considered. The effective dose calculated from our system data for two ankles is around 200 mGy*cm*0.0002 mSv/(mGy*cm) = 0.04 mSv or 0.02 mSv for only one OSG. Comparable data can be found in the literature (https://link.springer.com/article/10.1007/s00256-019-03309-7). The radiation dose for bilateral CT imaging of the ankle joints is approximately twice as high as for a unilateral examination; however, the total dose-length product remains very low and corresponds to an effective dose of less than 0.1 mSv. Given this minimal radiation exposure, the benefits of improved accuracy in postoperative assessment clearly outweigh the additional radiation exposure.

We have revised the relevant section, now on lines 294 through 307.

Line 294 – 307: The parameters describing the anatomy of the DTFJ vary by 4–8 mm for ATF, 6–13 mm for TFCS, and 13 mm for antTFD [16, 17, 18, 31]. Given these variations and the fact that a lateral difference of >2 mm after surgery is considered a malreduction, bilateral CT is superior to plain radiography for assessing DTFJ post-op congruity [2,11,12,19-22]. The findings of this study reinforce the recommendation that a unilateral CT scan is not a comprehensive assessment of postoperative congruity of the DTFJ. Based on the results and the literature, bilateral CT control was established as part of our post-operative routine following DTFJ stabilization in the treatment of ankle fractures [44,45]. In particular, the presence of a discrepancy between the anterior tibiofibular compression (ATF) and the tibiofibular compression stress (TFCS) of more than 2 mm in lateral comparison suggests that there may be a malreduction present, which potentially have a negative effect on the clinical outcome [2,3]. In our own treatment strategy, we recommend considering a revision of a syndesmotic malreduction for patients with a side difference of |ΔantTFD| and ΔLCS of more than 2 mm [2,3,12].

 

Comment 17: Would the authors consider dynamic CT assessment?

Response 17: As a consequence of our clinical and image morphological studies, we are currently working on a research project that examines dynamic CT scans of the ankle joint in neutral and external rotation positions on cadavers. We will report on the results.

We would like to express our sincere gratitude once again for the comprehensive and substantive review. It is our hope that the aforementioned concerns have been addressed to a satisfactory extent. Your review has contributed substantially to improving the work on a higher level.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Summary

The authors have conducted a retrospective case series of patients undergoing syndesmotic stabilization with a suture button technique. The authors sought to prove that “stabilisation via suture button systems can be performed regardless of anatomical variations.” The authors sought to demonstrate this by measuring a variety of radiographic parameters on supine computed tomography images that had helpfully been performed on a group of patients as part of their local standard of care.

 

Unfortunately, I have some concerns regarding this manuscript.

 

The authors repeatedly refer to measuring the “outcome” of “flexible nature of fixation” but do not measure any patient outcomes. Despite a number of reads, I still can’t work out how the authors were attempting to measure this outcome.

The authors mention some patients with over- or under- reduction but do not reassure the reader that these patients had their fixations revised. The authors suggest detection of malreduction is why a post-operative CT scan should be standard of care, and given the retrospective nature of the study and no mention of consenting patients for additional ionizing imaging. The authors excluded patients with fracture malreduction. The authors do not report how many patients were screened, or excluded.

The authors state this is a retrospective study but also state that “All individuals have given general consent in the use of their data, including imaging, for analysis and publication.”. Were patients contacted for consent? Did any elect not to participate?

The authors have reported results in the methods section. Classically results, like the ‘average’ (mean? median?) age of patients in the sample, let alone the results of hypothesis tests (“there was no difference”) should be reserved for the results section.

The authors report using separate assessors to measure the radiographic variables but do not report the agreement between the assessors.

The authors mention a difference of > 2 mm “side-to-side difference” as the threshold beyond which malreduction was considered. It is not clear in which measure the authors are making this assessment, nor is there a citation for it beyond the statement of “In accordance with existing literature”. In the following sentence the authors revise this to 1 mm, and cite a review article, and a textbook on sample size selection as a reason.

 

Finally, Figure 2 appears to demonstrate an intra-operative fracture around the fibular drill hole.

Comments on the Quality of English Language

See review.

Author Response

Dear reviewer, 
we would like to thank you very much for the  processing and editing of our article "Impact of distal tibio-fibular joint anatomy on reduction out-come in dynamic suture button stabilization of the distal syn-desmosis - a CT analysis" and for the possibility to resubmit it after  revision. (Ref.: traumacare-3262676)

Thank you for your suggestions for changes and improvements, which have markedly improved the quality of our study. We hope that we have processed them to your satisfaction.

 

Comments 1: The authors repeatedly refer to measuring the “outcome” of “flexible nature of fixation” but do not measure any patient outcomes. Despite a number of reads, I still can’t work out how the authors were attempting to measure this outcome.
Response 1: We thank you for the important comment and agree with this statement and would like to apologise for any confusion regarding the term ‘outcome’.
We performed a purely CT-based analysis and only analysed image morphological data. For this reason, we have replaced the term ‘outcome’ with ‘CT-morphological outcome’ throughout the manuscript to clarify this.

Line 190; 193; 208; 215; 227; 239; 264; 281; 

The section has been clarified in that the FNF has been quantified by the TO (transverse offset). A detailed description of the FNF, respective TO has also been added. Please refer to the previously published method and the attached reference number 17.

Line 130 to 139: Initially, the centres of the drill channel of the tibia (A and B) and fibula (C and D) were delineated in a line with the cortical bone. Subsequently, the tibia line was drawn from point A to B and the fibula line from point D to point C. The tibial line was extended to point B on the fibula side. The midpoint of the fibular line (F) was marked, and the perpendicular line from F was drawn to the lines A and B. The crossection was pointed as E.The measured distance from E to F is defined as TO and quantified the FNF of TightRope® stabilisation. It was assumed that the reduction was temporarily fixed before stabilisation and that the tibial and fibular lines, respectively the drill channels, did not deviate during the drilling and insertion of the SBS.

 

Comments 3: The authors mention some patients with over- or under- reduction but do not reassure the reader that these patients had their fixations revised. 
Response 3: Thank you for pointing this out. It was decided not to share this information with the readers as we did not believe it would contribute significantly to answering the questions posed. A paragraph has been added to address this issue. 

Line 259 to 262/ Discussion: In our own treatment strategy we recommend to consider a revision of a syndesmotic malreduction in patients with a discrepancy of |ΔantTFD|  and LCS of more than 2 mm. We perform this procedure after obtaining informed consent. 

 

Comments 4: The authors suggest detection of malreduction is why a post-operative CT scan should be standard of care, and given the retrospective nature of the study and no mention of consenting patients for additional ionizing imaging. 
Response 4: Thank you for pointing this out. Due to the large inter-individual anatomical differences and the inaccuracy of intraoperative fluoroscopy and postoperative conventional radiography for the assessment of syndesmosis reduction, DTFG computed tomography (CT) of both ankles is recommended according the literure published before patient inclusion if this study. The recommendation for belateral CT controll was established in the hospital's internal treatment standard according the literature. The manuscript has been adapted accordingly.  

Line 41 to 43: Furthermore, it has been shown that intraoperative fluoroscopy and postoperative conventional radiography are not accurate for the assessment of syndesmosis reduction.
Line 86 to 88: As part of the treatment of ankle fractures, the syndesmosis reduction is assessed by bilateral CT control, which is considered to be the hospital's internal standard in accordance with the literature.

 

Comments 5: The authors excluded patients with fracture malreduction. The authors do not report how many patients were screened, or excluded.
Response 5: Thank you for your valuable comment. We have reviewed the data and added the corresponding number of patients and the reasons for their exclusion. 

Line 67: This retrospective study included 44 (61%) out of 65 consecutive …..

Line 69 to 71: Thirteen patients with CT slice thickness of >1 mm, 11 patients with monolateral CT control and four patients with inadequate bony osteosynthesis were excluded from the study.

 

Comments 6: The authors state this is a retrospective study but also state that “All individuals have given general consent in the use of their data, including imaging, for analysis and publication.”. Were patients contacted for consent? Did any elect not to participate?
Response 6: All patients provided written consent for the use of their anonymized data, including imaging, for analysis and publication as outlined in the general treatment contract.
A corresponding section has been added.

 

Comments 7: The authors have reported results in the methods section. Classically results, like the ‘average’ (mean? median?) age of patients in the sample, let alone the results of hypothesis tests (“there was no difference”) should be reserved for the results section.
Response 7: We would like to thank you for this important feedback and have listed the relevant section as a separate paragraph under "Patients overview" in the results section.Line 167 to 170/ Results

 

Comments 8: The authors report using separate assessors to measure the radiographic variables but do not report the agreement between the assessors.
Response 8: We thank you for this item. The intra-rater and inter-rater reliabilities for the parameters describing the 'FNF' have previously been published, and the data was then added.
Line 128 to 126/Materials and Methods: The intra-rater and inter-rater reliabilities for the parameters describing the 'FNF' have been proven to be excellent (α > 0.90) [17].

 

Comments 9: The authors mention a difference of > 2 mm “side-to-side difference” as the threshold beyond which malreduction was considered. It is not clear in which measure the authors are making this assessment, nor is there a citation for it beyond the statement of “In accordance with existing literature”. In the following sentence the authors revise this to 1 mm, and cite a review article, and a textbook on sample size selection as a reason.
Response 9: The section explained why the threshold values at 1 mm was chosen as the definition of incongruence. In addition, the difference to malreduction should be noted. The aim of the study was to investigate the influence of anatomy on dynamic stabilisation. For this purpose, a very low threshold values was used. The corresponding text section was adapted and specified.
Line121 to 126: In order to facilitate comparison with results from the literature on static stabilisation with a syndesmotic screw, the threshold values in this analysis were set to more than 1.0 mm for ΔLCS, ΔaTFD and more than 5° for ΔNTDA as the definition of incongruence [1, 27, 34, 35]. This is to be distinguished from the definition of malreduction, which is de-fined as a difference of more than two millimetres from side to side for ΔLCS, ΔantTFD [1, 2].

 

Comments 10: Finally, Figure 2 appears to demonstrate an intra-operative fracture around the fibular drill hole.
Response 10: Thank you for your useful contribution. The image shows an anatomical fracture reduction and the bone interference observed does not correspond to a peri-implant fracture. This represents the fracture gap that can also be present in an anatomical reduction with slight bone deformation in out opinion. 
The images have been adjusted accordingly: Figure 2/Line142: The dotted line indicates a fracture gap that is still visible; the dashed line shows the plate and the suture button.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

I would like to thank the authors for allowing me to review this article. It has a simple message, and has been well executed with appropriate methodology and statistical testing. I do not have any critiques of this paper. 

 

Author Response

Dear Reviewer,

we would like to thank you for processing and editing our article, "Impact of distal tibio-fibular joint anatomy on reduction outcome in dynamic suture button stabilization of the distal syn-desmosis - a CT analysis".
We are grateful for your recommendation to publish the article.

On behalf of the authors

Reviewer 3 Report

Comments and Suggestions for Authors

Nicely performed study. I would like to suggest to accept this paper for publication

 

Thanks

Author Response

Dear Reviewer,

we would like to thank you for processing and editing our article, "Impact of distal tibio-fibular joint anatomy on reduction outcome in dynamic suture button stabilization of the distal syn-desmosis - a CT analysis".
We are grateful for your recommendation to publish the article.

On behalf of the authors