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Regarding “Biomechanical and Computed Tomography Analysis of Adjustable Femoral Cortical Fixation Devices for Anterior Cruciate Ligament Reconstruction in a Cadaveric Human Knee Model”
Letters to the Editor
Regarding “Biomechanical and Computed Tomography Analysis of Adjustable Femoral Cortical Fixation Devices for Anterior Cruciate Ligament Reconstruction in a Cadaveric Human Knee Model”
We would like to commend the authors of the article “Biomechanical and Computed Tomography Analysis of Adjustable Femoral Cortical Fixation Devices for Anterior Cruciate Ligament Reconstruction in a Cadaveric Human Knee Model” for their contribution to the growing body of biomechanical research regarding adjustable-loop femoral cortical suspension devices.1 The use of computed tomography scan to measure the loop distance between the cortical button and graft after cyclic loading is an innovative attempt to answer the question regarding whether or not adjustable-loop devices lengthen after implantation. The authors stated that cyclic testing of the postreconstructed cadaver models was performed at 15 of knee flexion with cyclic anteroposterior loading from 0 to 133.5 N for 1,000 cycles. It is uncertain how this method of anteroposterior anterior cruciate ligament loading compares with in vivo forces during normal knee motion. In vivo knee forces during common posteanterior cruciate ligament reconstruction rehabilitation activities have been estimated as high as 500 N,2 and knee cycles may be as high as 6,000 per day during normal activity. After only 1,000 cycles, the authors found a mean increase in the button-graft distance (representing loop lengthening) of 0.61 mm for the RigidLoop devices and 0.53 mm for the TightRope devices. As shown in Figure 5 in the article, at least 1 sample of each type of device lengthened as much as 1.3 mm. Although we agree that these values are unlikely to represent clinically significant lengthening, the question remains: would the loop lengthening continue if cyclic loading had continued? Other biomechanical studies have shown that as loading continues beyond 1,000 cycles, adjustable-loop devices continue to lengthen at a faster rate than fixed-loop suspension devices.3,4 If this lengthening is due to “slippage” of the adjustable-loop device’s friction-locking mechanism, then device failure potentially becomes dependent on the number of cycles experienced before graft incorporation. This seems to be highlighted by Figure 6, showing a significant increase in absolute laxity after cycling for both TightRope and RigidLoop groups.
In their discussion, the authors also mention the Barrow et al.3 article and potential for technical error that was proposed in a letter to the editor. The response to this letter shows that the increased lengthening was most likely related to differences in loading parameters (lower minimum load) and increased number of cycles.5 Through 1,000 cycles of testing this study actually reported less displacement in the adjustable-loop constructs than was seen in previous studies. Given the question of technical error, a video of the testing was also attached as a supplement to review. Again we would like to congratulate the authors on their research. Future studies comparing these results with a fixed-loop button at a higher number of cycles could provide valuable additional data regarding suspension device elongation.
Aaron E. Barrow, M.D. Travis C. Burns, M.D. Fort Sam Houston, Texas Note: The authors report that they have no conflicts of interest in the authorship and publication of this article. Published by Elsevier on behalf of the Arthroscopy Association of North America http://dx.doi.org/10.1016/j.arthro.2016.04.006
References 1. Born TR, Biercevicz AM, Koruprolu SC, Paller D, Spenciner D, Fadale PD. Biomechanical and computed tomography analysis of adjustable femoral cortical fixation devices for anterior cruciate ligament reconstruction in a cadaveric human knee model. Arthroscopy 2016;32: 253-261. 2. Johnson JS, Smith SD, LaPrade CM, Turnbull TL, LaPrade RF, Wijdicks CA. A biomechanical comparison of femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction under high loads. Am J Sports Med 2015;43:154-160. 3. Barrow AE, Pilia M, Guda T, Kadrmas WR, Burns TC. Femoral suspension devices for anterior cruciate ligament
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 32, No 7 (July), 2016: pp 1225-1230
1225
1226
LETTERS TO THE EDITOR
reconstruction: Do adjustable loops lengthen? Am J Sports Med 2014;42:343-349. 4. Eguchi A, Ochi M, Adachi N, Deie M, Nakamae A, Usman MA. Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: Comparison of the fixed-length loop device versus the adjustable-length loop device. Knee 2014;21:743-748. 5. Burns TC, Barrow AE, Pilia M, Guda T, Kadrmas WR. Femoral suspension devices for anterior cruciate ligament reconstruction: Response. Am J Sports Med 2014;42:343-349.
Authors’ Reply
First, we would like to thank the researchers from the San Antonio Military Medical Center who replied to our study and the editor of Arthroscopy: The Journal of Arthroscopic and Related Surgery who gave the opportunity for a debate on loop lengthening during cyclic loading. We strongly believe that a better understanding of the mechanical and biomechanical properties of adjustable-loop devices is needed to supplement the limited clinical results.1 We agree with Barrow and Burns that using computed tomography scans to measure the distance between the cortical button and the graft after cyclic loading could help to answer whether or not adjustable-loop devices lengthen after implantation. Because cadaveric models offer zero chance of measuring a healing response, we felt it most appropriate to focus on the immediate postoperative period and therefore chose our maximum load and number of cycles appropriately. Although we acknowledge that later on in the rehabilitation period, certain activities might increase the load across the graft to levels above our testing load of 133.5 N, we maintain that these are not the typical activities performed in the immediate postoperative period. Similarly, we are comfortable with the number of cycles used in our study as being representative of patients during the immediate postoperative period. During the later stages of rehabilitation, we agree that compliant patients will be placing thousands of cycles on their repaired limb each day. As was noted in the limitations, “This study made use of a cadaveric model, in which there is no influence of biological healing, remodeling, or dynamic stabilization; however, these results could reflect patient results at time zero.”2 With regard to the article from Barrow et al. and their subsequent response to a letter to the editor,3,4 we acknowledge the clarification of the portion of their study that concerned the potential for technical errors in the proper use of the Arthrex TightRope. However, again, as a pure biomechanical study, it only analyzed the mechanical properties of such devices, not taking into account the added support various anatomic static and dynamic stabilizers and biologic healing could
provide to an adjustable-loop device implanted into a human subject. We agree that translating these findings to anticipated clinical results still requires further research to be conducted in an attempt to provide practitioners with the necessary information to confidently employ such surgical techniques. As stated at the beginning of this letter, we are committed to continued dialog on loop lengthening during cyclic loading and look forward to additional investigations of this subject. Trevor R. Born, M.D. Providence, Rhode Island Dave Spenciner, P.E., Sc.M., M.B.A. Raynham, Massachusetts Paul D. Fadale, M.D. Providence, Rhode Island Ó 2016 by the Arthroscopy Association of North America http://dx.doi.org/10.1016/j.arthro.2016.04.007
References 1. Boyle MJ, Vovos TJ, Walker CG, Stabile KJ, Roth JM, Garrett WE Jr. Does adjustable-loop femoral cortical suspension loosen after anterior cruciate ligament reconstruction? A retrospective comparative study. Knee 2015;22:304-308. 2. Born TR, Biercevicz AM, Koruprolu SC, Paller D, Spenciner D, Fadale PD. Biomechanical and computed tomography analysis of adjustable femoral cortical fixation devices for anterior cruciate ligament reconstruction in a cadaveric human knee model. Arthroscopy 2016;32:253-261. 3. Barrow AE, Pilia M, Guda T, Kadrmas WR, Burns TC. Femoral suspension devices for anterior cruciate ligament reconstruction: Do adjustable loops lengthen? Am J Sports Med 2014;42:343-349. 4. Burns TC, Barrow AE, Pilia M, Guda T, Kadrmas WR. Femoral suspension devices for anterior cruciate ligament reconstruction: Response. Am J Sports Med 2014;42: NP16-NP18.
Regarding “Trends in Arthroscopic Procedures Performed During Orthopaedic Residency: An Analysis of Accreditation Council for Graduate Medical Education Case Log Data” I read with great interest the recent article by Hinds et al. titled “Trends in Arthroscopic Procedures Performed During Orthopaedic Residency: An Analysis of
Regarding “Biomechanical and Computed Tomography Analysis of Adjustable Femoral Cortical Fixation Devices for Anterior Cruciate Ligament Reconstruction in a Cadaveric Human Knee Model”
We would like to commend the authors of the article “Biomechanical and Computed Tomography Analysis of Adjustable Femoral Cortical Fixation Devices for Anterior Cruciate Ligament Reconstruction in a Cadaveric Human Knee Model” for their contribution to the growing body of biomechanical research regarding adjustable-loop femoral cortical suspension devices.1 The use of computed tomography scan to measure the loop distance between the cortical button and graft after cyclic loading is an innovative attempt to answer the question regarding whether or not adjustable-loop devices lengthen after implantation. The authors stated that cyclic testing of the postreconstructed cadaver models was performed at 15 of knee flexion with cyclic anteroposterior loading from 0 to 133.5 N for 1,000 cycles. It is uncertain how this method of anteroposterior anterior cruciate ligament loading compares with in vivo forces during normal knee motion. In vivo knee forces during common posteanterior cruciate ligament reconstruction rehabilitation activities have been estimated as high as 500 N,2 and knee cycles may be as high as 6,000 per day during normal activity. After only 1,000 cycles, the authors found a mean increase in the button-graft distance (representing loop lengthening) of 0.61 mm for the RigidLoop devices and 0.53 mm for the TightRope devices. As shown in Figure 5 in the article, at least 1 sample of each type of device lengthened as much as 1.3 mm. Although we agree that these values are unlikely to represent clinically significant lengthening, the question remains: would the loop lengthening continue if cyclic loading had continued? Other biomechanical studies have shown that as loading continues beyond 1,000 cycles, adjustable-loop devices continue to lengthen at a faster rate than fixed-loop suspension devices.3,4 If this lengthening is due to “slippage” of the adjustable-loop device’s friction-locking mechanism, then device failure potentially becomes dependent on the number of cycles experienced before graft incorporation. This seems to be highlighted by Figure 6, showing a significant increase in absolute laxity after cycling for both TightRope and RigidLoop groups.
In their discussion, the authors also mention the Barrow et al.3 article and potential for technical error that was proposed in a letter to the editor. The response to this letter shows that the increased lengthening was most likely related to differences in loading parameters (lower minimum load) and increased number of cycles.5 Through 1,000 cycles of testing this study actually reported less displacement in the adjustable-loop constructs than was seen in previous studies. Given the question of technical error, a video of the testing was also attached as a supplement to review. Again we would like to congratulate the authors on their research. Future studies comparing these results with a fixed-loop button at a higher number of cycles could provide valuable additional data regarding suspension device elongation.
Aaron E. Barrow, M.D. Travis C. Burns, M.D. Fort Sam Houston, Texas Note: The authors report that they have no conflicts of interest in the authorship and publication of this article. Published by Elsevier on behalf of the Arthroscopy Association of North America http://dx.doi.org/10.1016/j.arthro.2016.04.006
References 1. Born TR, Biercevicz AM, Koruprolu SC, Paller D, Spenciner D, Fadale PD. Biomechanical and computed tomography analysis of adjustable femoral cortical fixation devices for anterior cruciate ligament reconstruction in a cadaveric human knee model. Arthroscopy 2016;32: 253-261. 2. Johnson JS, Smith SD, LaPrade CM, Turnbull TL, LaPrade RF, Wijdicks CA. A biomechanical comparison of femoral cortical suspension devices for soft tissue anterior cruciate ligament reconstruction under high loads. Am J Sports Med 2015;43:154-160. 3. Barrow AE, Pilia M, Guda T, Kadrmas WR, Burns TC. Femoral suspension devices for anterior cruciate ligament
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 32, No 7 (July), 2016: pp 1225-1230
1225
1226
LETTERS TO THE EDITOR
reconstruction: Do adjustable loops lengthen? Am J Sports Med 2014;42:343-349. 4. Eguchi A, Ochi M, Adachi N, Deie M, Nakamae A, Usman MA. Mechanical properties of suspensory fixation devices for anterior cruciate ligament reconstruction: Comparison of the fixed-length loop device versus the adjustable-length loop device. Knee 2014;21:743-748. 5. Burns TC, Barrow AE, Pilia M, Guda T, Kadrmas WR. Femoral suspension devices for anterior cruciate ligament reconstruction: Response. Am J Sports Med 2014;42:343-349.
Authors’ Reply
First, we would like to thank the researchers from the San Antonio Military Medical Center who replied to our study and the editor of Arthroscopy: The Journal of Arthroscopic and Related Surgery who gave the opportunity for a debate on loop lengthening during cyclic loading. We strongly believe that a better understanding of the mechanical and biomechanical properties of adjustable-loop devices is needed to supplement the limited clinical results.1 We agree with Barrow and Burns that using computed tomography scans to measure the distance between the cortical button and the graft after cyclic loading could help to answer whether or not adjustable-loop devices lengthen after implantation. Because cadaveric models offer zero chance of measuring a healing response, we felt it most appropriate to focus on the immediate postoperative period and therefore chose our maximum load and number of cycles appropriately. Although we acknowledge that later on in the rehabilitation period, certain activities might increase the load across the graft to levels above our testing load of 133.5 N, we maintain that these are not the typical activities performed in the immediate postoperative period. Similarly, we are comfortable with the number of cycles used in our study as being representative of patients during the immediate postoperative period. During the later stages of rehabilitation, we agree that compliant patients will be placing thousands of cycles on their repaired limb each day. As was noted in the limitations, “This study made use of a cadaveric model, in which there is no influence of biological healing, remodeling, or dynamic stabilization; however, these results could reflect patient results at time zero.”2 With regard to the article from Barrow et al. and their subsequent response to a letter to the editor,3,4 we acknowledge the clarification of the portion of their study that concerned the potential for technical errors in the proper use of the Arthrex TightRope. However, again, as a pure biomechanical study, it only analyzed the mechanical properties of such devices, not taking into account the added support various anatomic static and dynamic stabilizers and biologic healing could
provide to an adjustable-loop device implanted into a human subject. We agree that translating these findings to anticipated clinical results still requires further research to be conducted in an attempt to provide practitioners with the necessary information to confidently employ such surgical techniques. As stated at the beginning of this letter, we are committed to continued dialog on loop lengthening during cyclic loading and look forward to additional investigations of this subject. Trevor R. Born, M.D. Providence, Rhode Island Dave Spenciner, P.E., Sc.M., M.B.A. Raynham, Massachusetts Paul D. Fadale, M.D. Providence, Rhode Island Ó 2016 by the Arthroscopy Association of North America http://dx.doi.org/10.1016/j.arthro.2016.04.007
References 1. Boyle MJ, Vovos TJ, Walker CG, Stabile KJ, Roth JM, Garrett WE Jr. Does adjustable-loop femoral cortical suspension loosen after anterior cruciate ligament reconstruction? A retrospective comparative study. Knee 2015;22:304-308. 2. Born TR, Biercevicz AM, Koruprolu SC, Paller D, Spenciner D, Fadale PD. Biomechanical and computed tomography analysis of adjustable femoral cortical fixation devices for anterior cruciate ligament reconstruction in a cadaveric human knee model. Arthroscopy 2016;32:253-261. 3. Barrow AE, Pilia M, Guda T, Kadrmas WR, Burns TC. Femoral suspension devices for anterior cruciate ligament reconstruction: Do adjustable loops lengthen? Am J Sports Med 2014;42:343-349. 4. Burns TC, Barrow AE, Pilia M, Guda T, Kadrmas WR. Femoral suspension devices for anterior cruciate ligament reconstruction: Response. Am J Sports Med 2014;42: NP16-NP18.
Regarding “Trends in Arthroscopic Procedures Performed During Orthopaedic Residency: An Analysis of Accreditation Council for Graduate Medical Education Case Log Data” I read with great interest the recent article by Hinds et al. titled “Trends in Arthroscopic Procedures Performed During Orthopaedic Residency: An Analysis of