Case Series: An Innovative Technique for Post-Corpectomy Reconstruction Using a Cage–Allograft/Autograft Construct

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

According to the authors, this is a series of cases in which they report an “innovative technique for post-multi-level corpectomy reconstruction” consistent with utilización use of mesh cages.

First, we must point out that mesh cages have been a widely used method in reconstructing corpectomy defects. I share with the authors the advantages of mesh cages over other more modern and sophisticated implants that do not allow the placement of significant amounts of bone to achieve fusion. This is crucial in this reconstructive surgery, especially when handling non-fatal cases.

In the Introduction, they claim, “To the best of our knowledge, we are the first to present our innovative postcorpectomy reconstruction technique, which involves using an allograft/autograft-cage construct, connected to the main rod using traversing pedicle screws.”

They then present 4 cases of this innovative technique:

1st case. T8 to T10 en bloc corpectomy and anterior column reconstruction were performed using a fibular allograft and a cage. It is not clear whether the fibular allograft was placed inside the mesh. It is specified that, in this case, there was no connection between the mesh and the posterior instrumentation.

2nd case. C4-C6 corpectomy and reconstruction with a mesh, fibular strut graft inside, and plate. The mesh was not attached to the plate. 

3rd case.  En-bloc resection of C1 through C3 and reconstruction with a mesh cage containing an embedded tricortical iliac crest graft. In this case, a lateral mass screw that was fastened to the rod as well was cannulated to the mesh.

4th case. A chronic Kummel lesion L2-L3 was treated with L2 corpectomy. The defect was reconstructed with a mesh filled with tricortical iliac crest autograft. In addition, a fibular allograft strut was placed within a meshed cage and wedged between the posterior elements to further promote stability and fusion. Both the anterior and posterior constructs were attached to the rods via a pedicle screw traversing the cage/bone graft unit.

Therefore, only the latter case can represent this innovative technique. In cases 1 and 2, they use a peroneal allograft, and in the other two cases, an iliac crest autograft inside the mesh. In cases 1 and 2, the mesh is not attached to posterior instrumentation.

Consequently, the study's conclusions do not coincide with the material presented. They cannot claim “Our innovative approach incorporates cages for stability, integrates allograft or autograft into the cage to eliminate the need for cage endcaps while promoting biological integration, and connects the construct to the rod using pedicle screws for enhanced stability” since only in one case have they practiced the innovative technique.

Author Response

Reviewer 1:

According to the authors, this is a series of cases in which they report an “innovative technique for post-multi-level corpectomy reconstruction” consistent with utilización use of mesh cages.

First, we must point out that mesh cages have been a widely used method in reconstructing corpectomy defects. I share with the authors the advantages of mesh cages over other more modern and sophisticated implants that do not allow the placement of significant amounts of bone to achieve fusion. This is crucial in this reconstructive surgery, especially when handling non-fatal cases.

In the Introduction, they claim, “To the best of our knowledge, we are the first to present our innovative postcorpectomy reconstruction technique, which involves using an allograft/autograft-cage construct, connected to the main rod using traversing pedicle screws.”

Thank you for pointing this out. We have now modified the intro:

In this case series, we present an innovative technique for post corpectomy reconstruction involving a cage construct integrated with posterior instrumentation. This approach combines the use of a mesh cage filled with autograft or allograft material, securely anchored to the spinal rod system using pedicle screws. By eliminating the need for endcaps and leveraging biological materials, this technique helps achieve both mechanical stability and biological integration.

They then present 4 cases of this innovative technique:

1st case. T8 to T10 en bloc corpectomy and anterior column reconstruction were performed using a fibular allograft and a cage. It is not clear whether the fibular allograft was placed inside the mesh. It is specified that, in this case, there was no connection between the mesh and the posterior instrumentation.

We have deleted case 1 entirely as per the other reviewer’s suggestion

2nd case. C4-C6 corpectomy and reconstruction with a mesh, fibular strut graft inside, and plate. The mesh was not attached to the plate. 

We have deleted case 2 entirely as per the other reviewer’s suggestion

3rd case.  En-bloc resection of C1 through C3 and reconstruction with a mesh cage containing an embedded tricortical iliac crest graft. In this case, a lateral mass screw that was fastened to the rod as well was cannulated to the mesh.

4th case. A chronic Kummel lesion L2-L3 was treated with L2 corpectomy. The defect was reconstructed with a mesh filled with tricortical iliac crest autograft. In addition, a fibular allograft strut was placed within a meshed cage and wedged between the posterior elements to further promote stability and fusion. Both the anterior and posterior constructs were attached to the rods via a pedicle screw traversing the cage/bone graft unit.

Therefore, only the latter case can represent this innovative technique. In cases 1 and 2, they use a peroneal allograft, and in the other two cases, an iliac crest autograft inside the mesh. In cases 1 and 2, the mesh is not attached to posterior instrumentation.

Consequently, the study's conclusions do not coincide with the material presented. They cannot claim “Our innovative approach incorporates cages for stability, integrates allograft or autograft into the cage to eliminate the need for cage endcaps while promoting biological integration, and connects the construct to the rod using pedicle screws for enhanced stability” since only in one case have they practiced the innovative technique. We have modified the conclusion to include: Our surgical technique highlights an innovative postcorpectomy reconstruction technique involving a mesh cage construct integrated with autograft/allograft and connected to posterior instrumentation for enhanced stability. The technique was applied successfully in two cases, demonstrating its feasibility and potential for promoting biological integration.

Reviewer 2 Report

Comments and Suggestions for Authors

Author stated that the "novel technique involved shaping the allograft/autograft to fit precisely within the cage, extending beyond its ends to facilitate fusion at both ends, and securing the construct to the spinal rods with pedicle screws for added stability...By incorporating allograft/autograft directly within the cage connected to the rods, the need for endcaps is potentially eliminated, reducing donor site morbidity linked with traditional grafts"

Case #1- For revision, was the mesh cage re-used and re-positioned followed by adding 2 new rods to create the quad rod construct?  

Case #2- Mesh cage and intra cage allograft used as described in the introduction.  No posterior screw linkage to the posterior rod.

Case# 3- Most interesting with posterior only construct with graft -in-cage .  Was the tricortical graft morselized to fill in the cage since the graft is not cylindrical shape like the mesh cage?

Case #4- In addition to the anterior cage, additional posterior interspinous graft-cage fastened to posterior rods for added stability?  Interesting concept but unclear why this was necessary since the anterior construct and posterior segmental instrumentation seemed quite adequate.

The graft-in-cage require additional time for shaving and shaping the graft to fit inside the cage, exposing patients to prolong anesthesia and additional OR time and cost.  I see no advantage of this construct over allograft/autograft alone or mesh cage alone.  Risk of subsidence and pistoning effect can be mitigated by adding endcaps to the cage or posterior construct augmentation.    For graft-anterior plate only construct, one or two screws can be inserted into the graft through the empty holes in the middle of the plate to anchor the graft into the plate, thus reducing the risk of graft shifting or subsiding.  This is similar to the concept of inserting pedicle screws into the graft from the posterior rod for added stabilization.

Conclusion  "Our surgical technique demonstrates promise in achieving stabilization, fusion, and alleviating neurologic symptoms. Our approach offers a valuable strategy for surgeries requiring corpectomies, providing the potential to improve outcomes and minimize complications at low cost." is not supported by the data.  Alleviating neurological symptoms was achieved by corpectomy.  Stabilization and fusion achieved by cage and graft with instrumentation, regardless of how cage and graft was used separately or together.  Lower cost has to be proven since additional OR and anesthesia time is needed for shaping the graft for proper fitting into the cage. 

The more interesting concept of this paper was the use of posterior mesh cage construct in case 3 and case 4.  Building a series of more cases of posterior only or posterior interspinous mesh cage would be more interesting to the readers.

Author Response

Reviewer 2:

Author stated that the "novel technique involved shaping the allograft/autograft to fit precisely within the cage, extending beyond its ends to facilitate fusion at both ends, and securing the construct to the spinal rods with pedicle screws for added stability...By incorporating allograft/autograft directly within the cage connected to the rods, the need for endcaps is potentially eliminated, reducing donor site morbidity linked with traditional grafts"

Case #1- For revision, was the mesh cage re-used and re-positioned followed by adding 2 new rods to create the quad rod construct?  

We have deleted case 1 entirely as per your suggestion.

Case #2- Mesh cage and intra cage allograft used as described in the introduction.  No posterior screw linkage to the posterior rod.

We have deleted case 2 entirely as per your suggestion.

Case# 3- Most interesting with posterior only construct with graft -in-cage .  Was the tricortical graft morselized to fill in the cage since the graft is not cylindrical shape like the mesh cage? Yes

Case #4- In addition to the anterior cage, additional posterior interspinous graft-cage fastened to posterior rods for added stability?  Interesting concept but unclear why this was necessary since the anterior construct and posterior segmental instrumentation seemed quite adequate. We added the posterior interspinous graft-cage to provide extra stability beyond what the anterior cage and posterior segmental instrumentation alone could offer. This was intended to create a more secure construct and reduce the risk of potential failure or subsidence, especially in high-stress areas. While this approach was developed intraoperatively as an innovative solution, we acknowledge that we currently do not have formal evidence to support its efficacy

The graft-in-cage require additional time for shaving and shaping the graft to fit inside the cage, exposing patients to prolong anesthesia and additional OR time and cost.  I see no advantage of this construct over allograft/autograft alone or mesh cage alone.  Risk of subsidence and pistoning effect can be mitigated by adding endcaps to the cage or posterior construct augmentation.  The time spent was not long to prepare and shape the allograft. I agree that the time may be longer, but it allows for shaping the fibula and docking it in the endplates, which promotes fusion. Additionally, end caps do not allow for fusion, and having the bone graft extend beyond the length of the cage and in contact with the endplates above and below would, theoretically, allow for bone-to-bone healing.

For graft-anterior plate only construct, one or two screws can be inserted into the graft through the empty holes in the middle of the plate to anchor the graft into the plate, thus reducing the risk of graft shifting or subsiding.  This is similar to the concept of inserting pedicle screws into the graft from the posterior rod for added stabilization.

Conclusion  "Our surgical technique demonstrates promise in achieving stabilization, fusion, and alleviating neurologic symptoms. Our approach offers a valuable strategy for surgeries requiring corpectomies, providing the potential to improve outcomes and minimize complications at low cost." is not supported by the data. Alleviating neurological symptoms was achieved by corpectomy.  We have therefore deleted this part. Stabilization and fusion achieved by cage and graft with instrumentation, regardless of how cage and graft was used separately or together.  Lower cost has to be proven since additional OR and anesthesia time is needed for shaping the graft for proper fitting into the cage. We have deleted this part as well.

Instead we modified the conclusion to include: Through the presentation of two illustrative cases spanning the cervical and lumbar spine, we showcased the application and effectiveness of our approach. Our surgical technique highlights an innovative postcorpectomy reconstruction technique involving a mesh cage construct integrated with autograft/allograft and connected to posterior instrumentation for enhanced stability. The technique was applied successfully in two cases, demonstrating its feasibility and potential for promoting biological integration.

The more interesting concept of this paper was the use of posterior mesh cage construct in case 3 and case 4.  Building a series of more cases of posterior only or posterior interspinous mesh cage would be more interesting to the readers.

Thank you for your input. We have done exactly this and just kept cases 3 and 4 in our manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for this interesting case series.

I have the following remarks.

Abstract Results: 

In all four cases, the technique was utilised succesfully, achieving ... Please adapt

Conclusion. The level of evidence is rather low. The innovative technique could offer.... Please adapt

The conclusion concerning the use of end caps is not part of the cases series. the conclusion concerning reducing donor site morbidity is also nor part of the case series. Please remove these conclusions

Introduction:

and added risk. please add referenceulsion

expulsion: dislocation instead of expulsion

Reference 2 is not concerning a clinical study. Please correct

Reference 6 is concerning a fibular graft not iliac. Please correct

Reference 6 and 7 seem to be mispositioned

Reference 9 and 13 are incorrectly used

Reference 13 should be 13and 14

Connected to the main rod does not seem to be true in all cases. 

The use of cement seems to be contradictory to bone fusion.

Please explain in the discussion wy PMMA was used

eliminating the need for end caps. This statement is misleading.

Only one pedicle screw? Biomechnically this is suboptimal. Please discuss accordingly

Case 1: cage is not connected to the main stabilizing rods. Please correct the description in the introduction

Case 2:

Hypermetabolic instead og hyperbolic

Cage stabilised with a plate and not corrected to the main rods. Please correct. This technique  certainly is not new.

Case 3:

Figure 13. No complete fusion. Only proximally. Please correct

Please describe how the pedicle screws were stabilised within the cage

Case 4: 

Screw purchase in the cage is not clear and seems to be relying on only one screw if any. Please discuss

Discussion:

We take pride... This statement in not in line with the case descriptions.

Conclusions:

Please align with the abstract

Author Response

Reviewer 3:

Thank you for this interesting case series.

I have the following remarks.

Thank you for your remarks!

Abstract Results: 

In all four cases, the technique was utilised succesfully, achieving ... Please adapt

Conclusion. The level of evidence is rather low. The innovative technique could offer.... Please adapt.

We adapted the sentence as per your recommendation.

The conclusion concerning the use of end caps is not part of the cases series. the conclusion concerning reducing donor site morbidity is also nor part of the case series. Please remove these conclusions. We have deleted this sentence.

**please note for all the references, they have been modified to a different citation number as we added references to abstract

please add referenceulsion and added risk: We have added references to the abstract.

Introduction

expulsion: dislocation instead of expulsion:

Thank you we have made this change.

Reference 2 is not concerning a clinical study. Please correct

We have modified the reference used.

Reference 6 is concerning a fibular graft not iliac. Please correct.

Thank you we have made this change.

Reference 6 and 7 seem to be mispositioned

They are in the correct position now.

Reference 9 and 13 are incorrectly used

For Ref 9, we don’t see why it is incorrectly used for the sentence: “The outcomes of allograft utilization in multilevel reconstructions vary, with some studies reported promising fusion rates with fibular allografts”

Below are some abstracts from Reference 9 explaining why we used it:

From the article you provided, here are relevant extracts that can be cited to support your sentence:

1. Promising Fusion Rates:
• "Radiographic analysis of these 83 segmental fusions revealed that 70% of the grafts obtained union by 6 months after surgery. Twenty-two percent of the grafts had less than 50% trabecula bridging at one vertebral end plate and hence were deemed partial unions. Thus, 92% of the grafts achieved either complete or partial union by 6 months."
2. Utilization of Fibular Allografts in Multilevel Reconstructions:
• "Twelve patients had a one-level interbody fusion, 20 a two-level fusion, 9 a three-level fusion, and 1 a four-level fusion. A total of 83 freeze-dried fibular allografts were placed in these patients."
3. Clinical and Radiographic Outcomes:
• "Eighty-eight percent of the patients were found to have excellent or good clinical results. Radiographic follow-up revealed that 92% of the grafts obtained complete or partial union by 6 months after surgery."

For Ref 13: We have removed it from the sentence where it was previously.

Reference 13 should be 13and 14 We have made your recommended change.

Connected to the main rod does not seem to be true in all cases.  We have deleted and modified this sentence.

The use of cement seems to be contradictory to bone fusion. The case was deleted as it represented a different approach.

Please explain in the discussion wy PMMA was used. The case was deleted as it represented a different approach.

eliminating the need for end caps. This statement is misleading. The end caps do not allow for fusion, and having the bone graft extend beyond the length of the cage and in contact with the endplates above and below would, theoretically, allow for bone-to-bone healing.

Only one pedicle screw? Biomechnically this is suboptimal. Please discuss accordingly. The pedicle screw is an additional screw placed alongside the cage, complementing the other screws to provide extra stability.

Case 1: cage is not connected to the main stabilizing rods. Please correct the description in the introduction We have deleted case 1 entirely as per the other reviewer’s suggestion

Case 2:

Hypermetabolic instead og hyperbolic: We have deleted case 2 entirely as per the other reviewer’s suggestion

Cage stabilised with a plate and not corrected to the main rods. Please correct. This technique  certainly is not new. We have deleted case 2 entirely as per the other reviewer’s suggestion

Case 3:

Figure 13. No complete fusion. Only proximally. Please correct. We have deleted this figure as its from what was previously labeled as case #2.

Please describe how the pedicle screws were stabilised within the cage. This is explained in lines 23-26. These sentences describe the shaping and placement of the graft within the cage, followed by drilling through the graft and inserting a pedicle screw through the cage and into the graft to cannulate the construct. The screw is then connected to the final rod to provide additional stability to the system

Case 4: 

Screw purchase in the cage is not clear and seems to be relying on only one screw if any. Please discuss

Both the anterior and posterior constructs were attached to the rods using one pedicle screw traversing the anterior cage and two pedicle screws traversing the posterior cage/bone graft unit (lines 12-13)

Discussion:

We take pride... This statement in not in line with the case descriptions.

The sentence has been changed to: Notably, our technique represents a novel advancement, with the integration of a pedicle screw through the cage demonstrating significant biomechanical and clinical benefits.

This is demonstrated:

Case #1: The construct includes a mesh cage with an embedded tricortical iliac crest graft. The cage is cannulated with a lateral mass screw that is fastened to the rod, providing robust stabilization. The pedicle screw traverses the cage to enhance stability.

Case #2: A cage filled with tricortical iliac crest autograft is placed anteriorly, and the construct is attached to the rods via a pedicle screw traversing the cage/bone graft construct. The pedicle screw is integrated through the cage.

Conclusions:

Please align with the abstract. We have deleted the sentence that was recommended to delete.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have significantly modified the paper's content following this reviewer's comments.

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript is much more focus and concise in the description of this innovative technique.  I applaud the authors for presenting their novel idea and thoughtful surgical management of these very challenging cases as presented.  Very interesting novel idea that can be built into a very good series over time.  I'm eagerly await the next report on this series.

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for the adaptations