The Journal of Arthroplasty xxx (2014) xxx–xxx
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty William M. Mihalko, MD, PhD a, Erik L. Woodard, MS a, Casey T. Hebert, MS a, John R. Crockarell, MD a, John L. Williams, PhD b a b
University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery & Biomedical, Engineering, Memphis, Tennessee University of Memphis Department of Biomedical Engineering, 330 Engineering Technology Building, Memphis, Tennessee
a r t i c l e
i n f o
Article history: Received 29 July 2014 Accepted 5 September 2014 Available online xxxx Keywords: total arthroplasty varus knee gap balancing pie-crusting technique cadaver biomechanical study
a b s t r a c t Balancing a varus knee is traditionally accomplished by releasing the medial soft-tissue sleeve off the tibia. Recently, “pie-crusting” (PC) medial structures has been described. In a biomechanical cadaver study we compared PC to traditional release (TR) to determine their effects on flexion and extension gaps. PC was done in five specimens along the anterior half of the medial soft-tissue sleeve and five along the posterior half, followed by a traditional release. In 90° flexion, valgus laxity after TR was significantly greater than after PC alone. PC of the anterior or posterior aspect of the medial soft-tissue sleeve can effect changes more in flexion than in extension, respectively. Complete TR did not provide more gap opening than PC in extension, but produced more effect in flexion. © 2014 Elsevier Inc. All rights reserved.
Soft-tissue or gap balancing is an important part of total knee arthroplasty (TKA) surgery, especially in osteoarthritic knees with varus deformity. Traditionally, balancing has been done by subperiosteally releasing portions of the medial soft-tissue sleeve off the proximal tibia [1–13], but this may lead to excessive laxity (especially when the posterior cruciate ligament is sacrificed) or residual pain about the area where the release was done [4,10,13–17]. A “pie-crusting” (PC) or “inside-out” technique has been described to balance the varus knee without compromising the structural integrity of the ligamentous structures and without subperiosteal (traditional) release [1,5,6,18–24]. Compared to isolated releases along the posterior aspect of the proximal tibia, releasing the anterior aspect of the medial softtissue sleeve may produce a larger increase in the joint gap in flexion than in extension [11,23]. Whiteside et al [11] compared the effects of a traditional release of the anterior portion of the medial collateral ligament (MCL) to the effects of release of the posterior aspect of the MCL and the posterior oblique ligament and found that anterior release had a greater effect on the flexion gap while the posterior release affected mainly the extension gap.
All research for this study took place at the University of Tennessee-Campbell Clinic Dept. of Orthopaedic Surgery & Biomedical Engineering. Each author certifies that he has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.09.005. Reprint requests: William M. Mihalko, MD, PhD, University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery & Biomedical, Engineering, 1211 Union Avenue, Suite 510, Memphis TN 38104.
If pie-crusting techniques on the medial side of the knee can obtain equal effects in flexion and extension, there would be obvious advantages over complete ligament release. The purposes of this study were to determine what parts of the medial soft-tissue sleeve affect the gap in flexion or extension and to compare the results of pie-crusting to an additional standard medial release [4]. Our hypothesis was that pie crusting would be as effective as a traditional subperiosteal release and that targeting the anterior and posterior aspects of the medial soft-tissue sleeve would have more effect on the flexion and extension gaps, respectively. Material and Methods The specimens used in this study were lower extremities from fresh cadavers of donors who had undergone a previous primary TKA (Medical Education and Research Institute, Memphis, TN, and Restore Life USA, Johnson City, TN). IRB approval was obtained before beginning the study. Fourteen knee specimens (5 left and 9 right) were retrieved and all skin, subcutaneous tissue, and muscle were removed, while all aspects of the knee capsule and surrounding ligaments were carefully retained. Each specimen underwent fluoroscopic imaging to confirm no signs of aseptic loosening or bearing wear was present. The femur and tibia were cut transversely 180 mm proximal and distal to the knee joint line, the proximal tibio-fibular joint was left intact, and the fibular shaft was transected 100 mm from the joint line. The femur and tibia of each specimen were potted with urethane epoxy (Goldenwest MFG Inc, Cedar Ridge, CA) in a coupling that allowed mounting into a custom knee testing machine that has been validated in previous studies (Fig. 1) [11,17,23]. Specimens were placed with the tibia mounted
http://dx.doi.org/10.1016/j.arth.2014.09.005 0883-5403/© 2014 Elsevier Inc. All rights reserved.
Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005
2
W.M. Mihalko et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
Fig. 2. An example of the pie crusting performed on the SMCL of a right TKA specimen with the 11 blade in a checkerboard type pattern of 3–4 mm.
determine rotational laxity. Paired t-tests with a Holms–Sidak correction were used to determine statistical significance between tests. A corrected P-value was then calculated based on the number of comparisons between groups to determine overall statistically significant differences between groups. Fig. 1. One of the cadaveric specimens prepared and mounted into the custom knee testing machine. The machine allows for adjustment to place each specimen in its anatomic position with the epicondylar axis aligned with the femoral attached cross head.
vertically in the machine and the femoral coupling locked in a neutral position as defined by the vertically placed tibia. Specimens were tested with the knee joint at full extension and at 30, 60, and 90 degrees of flexion. An applied body weight force of 30 N was placed under the tibia to maintain joint contact during all tests. At each flexion angle, a 1.5-Nm internal and external rotational torque was applied about the tibial axis while the femur was fixed and the tibia was free to rotate about the joint center in the coronal plane. A 10-Nm varus and valgus torque also was applied to each specimen on the tibia, while internal– external rotation was unconstrained. Each test was performed three times initially to pre-condition each specimen with the third iteration utilized for each testing condition. A fellowship-trained, board-certified orthopedic surgeon then performed a standard medial parapatellar arthrotomy to gain access into the knee capsule. With a number 11 scalpel, alternating 3- to 4-mm stab incisions were made on the anterior aspect of the superficial medial collateral ligament (SMCL) from the medial epicondyle to the tibial insertion on 7 specimens (Fig. 2). The same procedure was done on the posterior aspect of the SMCL in the other 7 specimens. Each specimen was randomly assigned into one of the groups. Pie crusting was then done on the opposite portion of the SMCL and medial soft-tissue structures on all specimens, resulting in a “complete” PC technique. The medial soft-tissue sleeve was then released from its attachment on the proximal tibia from the joint line to a point 5 cm distally. After each step of the procedure, testing was done with the same loads and positions as the native TKA specimen. The angular deflection in degrees at ± 10 Nm of valgus torque in the coronal plane referenced from normal neutral position was recorded to determine the valgus laxity for each test. Likewise, the deflection in degrees at ± 1.5 Nm internal and external torque in the transverse plane referenced from the normal neutral position was recorded to
Results No significant changes in varus laxity from normal TKA knees were found when the surgical procedures were compared. Posterior piecrusting had a greater effect on valgus laxity at all flexion angles than did anterior pie-crusting. Anterior pie-crusting increased valgus laxity by 1.0 ± 0.2 degrees in full extension and 1.4 ± 0.6 degrees at 90 degrees of flexion. In comparison, posterior pie-crusting increased valgus laxity by 3.1 ± 1.2 degrees in extension and 3.0 ± 1.0 degrees in flexion. Complete pie-crusting and a traditional ligament release produced essentially the same changes (0.1 degree difference) in valgus laxity at full extension, but the traditional ligament release had a significantly greater effect at 60 and 90 degrees of flexion, increasing laxity by 1.4 and 2.5 degrees over pie-crusting, respectively (Fig. 3). No significant differences were found between pie crusting and ligament release in external rotation (Fig. 4A), but the difference was significant at all flexion angles in internal rotation when traditional release was compared to all of the pie-crusting release groups tested (Fig. 4B). Anterior pie-crusting had a greater effect on rotational laxity in flexion than extension, increasing internal and external laxity by 2.8 ± 0.4 and 2.7 ± 0.9 degrees, respectively, at 90 degrees of flexion. In comparison, internal and external laxity increased by 0.9 ± 0.3 and 0.14 ± 0.2 degrees in extension. Discussion As with previously reported studies concerning traditional release of the anterior and posterior portions of the MCL and posterior oblique ligament [11,25,26], anterior PC produced a greater change in laxity from normal conditions in flexion compared to full extension [25]. Likewise, PC of the posterior aspect of the medial soft-tissue sleeve (SMCL and posterior oblique ligament) produced greater laxity changes at full extension and 30 degrees of flexion, where these structures are most supportive. Overall, PC and ligament release produced increasingly greater changes in laxity as the flexion angle increased, but the traditional release did effect a greater overall change in flexion, with no difference in
Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005
W.M. Mihalko et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
3
Fig. 3. Valgus laxity changes for each surgical technique group tested. The bar graphs represent the means and standard error measures for each surgical technique group tested as compared to the native TKA specimen.
full extension. This suggests that while a traditional complete ligament release may compromise stability in flexion, PC may effect symmetric changes in the extension and flexion gaps. With severe varus deformity, however, PC may not provide enough release to balance the medial
joint gap. Our study showed that a traditional release can be added after PC to effect more change in flexion and full extension. Menghini et al [22] compared the biomechanical stiffness and failure mechanisms of pie-crusting to those of traditional release of the MCL in
Fig. 4. External (A) and internal (B) rotational laxity changes for each surgical technique group tested. The bar graphs represent the means and standard error measures for each surgical technique group tested as compared to the native TKA specimen.
Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005
4
W.M. Mihalko et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
18 fresh-frozen cadaver specimen pairs. They reported that the piecrusted MCLs had a lower stiffness than those with a traditional release, but the difference was not statistically significant. The pie-crusted MCLs failed at the joint line with a tearing type of failure while the traditionally released MCLs failed at the tibial insertion of the MCL. In our study, no specimen failed under the moments that were used. Menghini et al tested only the MCL without supporting ligaments, while we tested the entire soft-tissue sleeve, which included the anterior portions of the joint capsule, MCL, posterior oblique ligament, and posteromedial capsule including portions of the semimembranosus tendon insertion. Our purpose was to determine how pie-crusting would affect the medial joint gap from full extension to 90 degrees of flexion using the anterior and/or posterior or full medial soft tissue sleeve. Whiteside et al [11] tested a traditional release technique targeting the anterior or posterior half of the medial soft-tissue sleeve using the same knee testing machine as our study and found that anterior release had a greater effect on the flexion gap while the posterior release affected mainly the extension gap. Our results were similar except that the PC technique produced lower valgus deflection change when the anterior or the posterior halves were targeted, but when a traditional release was added there were similar overall values. In internal rotation the largest recorded changes were with the traditional release, while PC effected significantly smaller changes compared to normal. If rotational laxity is far greater with a traditional release than with a PC technique, this may have a meaningful effect on stability of the TKA during the postoperative rehabilitation period. Whether these changes are clinically significant, however, still remains in question. Limitations of this study include the small sample size and variations in the patient age and implant type, leading to large differences in normal laxity among the specimens. Further, we used specimens that already had a functioning TKA in place for over 10 years and did not have a contracted medial soft-tissue sleeve. While it is safe to assume that these specimens underwent some type of soft tissue balancing during initial TKA surgery, each specimen was used as its own control, so only changes from the normal functioning state are presented here. It should also be noted that we are comparing changes in coronal laxity within each specimen where variations in the condylar and polyethylene conformity afford the least amount of constraint (i.e. differences in implant conformity effects the AP and transverse plane stability more than coronal plane stability). Pie-crusting also was done with an “outside-in” rather than an “inside-out” technique because of the presence of the implants. Another limitation is the fact that the specimens had implants from different manufacturer in place. While this would not affect coronal plane deflections, transverse plane laxity measures might have been affected by the varying amounts of conformity of the different implant designs (7 posterior-stabilized designs and 7 cruciate-retaining designs). Two specimens had functioning posterior cruciate ligaments (PCL) in place. Because the PCL acts as a secondary coronal plane stabilizer [27], this could have caused variations in coronal plane laxity measures, but the fact that each specimen was compared to its own intact status should have minimized these effects. Despite these limitations, this study clearly showed that a PC technique that targets the anterior aspect of the medial soft-tissue sleeve can effect a change in flexion with minimal change in extension, while PC of the posterior half of the medial soft-tissue sleeve can effect a significant change in extension as well as flexion. Pie-crusting of the entire softtissue sleeve also may have an advantage in that it effectively changes the flexion and extension gap in a more symmetrical manner than an additional traditional release. If a larger medial gap is still needed in flexion, releasing the MCL would be a viable approach after pie-crusting.
Acknowledgments The authors wish to thank Kay Daugherty the Campbell Foundation Medical Editor for her aid in preparing this manuscript. No grant funding was utilized for this study.
References 1. Bellemans J. Multiple needle puncturing: balancing the varus knee. Orthopedics 2011;34:e510. 2. Koh HS, In Y. Semimembranosus release as the second step of soft tissue balancing in varus total knee arthroplasty. J Arthroplasty 2013;28:273. 3. Lee BS, Lee SJ, Kim JM, et al. No impact of severe varus deformity on clinical outcome after posterior stabilized total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2011;19:960. 4. Matsueda M, Gengerke TR, Murphy M, et al. Soft tissue release in total knee arthroplasty. Cadaver study using knees without deformities. Clin Orthop Relat Res 1999;366:264. 5. Matsumoto T, Muratsu H, Kubo S, et al. Intraoperative soft tissue balance reflects minimum 5-year midterm outcomes in cruciate-retaining and posterior-stabilized total knee arthroplasty. J Arthroplasty 2012;27:1723. 6. Meftah M, Blum YC, Raja D, et al. Correcting fixed varus deformity with flexion contracture during total knee arthroplasty: the “inside-out” technique: AAOS exhibit selection. J Bone Joint Surg Am 2012;94:e66. 7. Mullaji A, Sharma A, Marawar S, et al. Quantification of effect of sequential posteromedial release on flexion and extension gaps: a computer-assisted study in cadaveric knees. J Arthroplasty 2009;24:795. 8. Picard F, Deakin AH, Clarke IV, et al. A quantitative method of effective soft tissue management for varus knees in total knee replacement surgery using navigational techniques. Proc Inst Mech Eng H 2007;221:763. 9. Verdonk PC, Pernin J, Pinaroli A, et al. Soft tissue balancing in varus total knee arthroplasty: an algorithmic approach. Knee Surg Sports Traumatol Arthrosc 2009; 17:660. 10. Whiteside LA, Mihalko WM. Surgical procedure for flexion contracture and recurvatum in total knee arthroplasty. Clin Orthop Relat Res 2002;404:189. 11. Whiteside LA, Saeki K, Mihalko WM. Functional medial ligament balancing in total knee arthroplasty. Clin Orthop Relat Res 2000;380:45. 12. Winemaker MJ. Perfect balance in total knee arthroplasty: the elusive compromise. J Arthroplasty 2002;17:2. 13. Yagishita K, Muneta T, Ikeda H. Step-by-step measurements of soft tissue balancing during total knee arthroplasty for patients with varus knees. J Arthroplasty 2003; 18:313. 14. Krackow KA, Mihalko WM. Flexion-extension joint changes after lateral structure release for valgus deformity correction in total knee arthroplasty. J Arthroplasty 1999;14:994. 15. Krackow KA, Mihalko WM. The effect of medial release on flexion and extension gaps in cadaveric knees: implications for soft-tissue balancing in total knee arthroplasty. Am J Knee Surg 1999;12:222. 16. Mihalko WM, Saleh KJ, Krackow KA, et al. Soft-tissue balancing during total knee arthroplasty in the varus knee. J Am Acad Orthop Surg 2009;17:766. 17. Saeki K, Mihalko WM, Patel V, et al. Stability after medial collateral ligament release in total knee arthroplasty. Clin Orthop Relat Res 2001;392:184. 18. Aglietti P, Lup D, Cuomo P, et al. Total knee arthroplasty using a pie-crusting technique for valgus deformity. Clin Orthop Relat Res 2007;464:73. 19. Bellemans J, Vandenneucker H, Van Lauwe J, et al. A new surgical technique for medial collateral ligament balancing: multiple needle puncturing. J Arthroplasty 2010;25:1151. 20. Clarke HD, Fuchs R, Scuderi GR, et al. Clinical results in valgus total knee arthroplasty with the “pie crust” technique of lateral soft tissue releases. J Arthroplasty 2005;20:1010. 21. Elkus M, Ranawat CS, Rasquinha VJ, et al. Total knee arthroplasty for severe valgus deformity. Five to fourteen-year follow-up. J Bone Joint Surg Am 2004;86:2671. 22. Meneghini RM, Daluga AT, Sturgis LA, et al. Is the pie-crusting technique safe for MCL release in varus deformity correction in total knee arthroplasty? J Arthroplasty 2013; 28:1306. 23. Mihalko WM, Krackow KA. Anatomic and biomechanical aspects of pie crusting posterolateral structures for valgus deformity correction in total knee arthroplasty: a cadaveric study. J Arthroplasty 2000;15:347. 24. Ranawat AS, Ranawat CS, Elkus M, et al. Total knee arthroplasty for severe valgus deformity. J Bone Joint Surg Am 2005;87(Suppl 1(Pt 2)):271. 25. Mihalko WM, Whiteside LA, Krackow KA. Comparison of ligament-balancing techniques during total knee arthroplasty. J Bone Joint Surg Am 2003;85(Suppl 4):132. 26. Mihalko WM, Whiteside LA. Bone resection and ligament treatment for flexion contracture in knee arthroplasty. Clin Orthop Relat Res 2003;406:141. 27. Mihalko WM, Miller C, Krackow KA. Total knee arthroplasty ligament balancing and gap kinematics with posterior cruciate ligament retention and sacrifice. Am J Orthop (Belle Mead NJ) 2000;29:610.
Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005
Contents lists available at ScienceDirect
The Journal of Arthroplasty journal homepage: www.arthroplastyjournal.org
Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty William M. Mihalko, MD, PhD a, Erik L. Woodard, MS a, Casey T. Hebert, MS a, John R. Crockarell, MD a, John L. Williams, PhD b a b
University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery & Biomedical, Engineering, Memphis, Tennessee University of Memphis Department of Biomedical Engineering, 330 Engineering Technology Building, Memphis, Tennessee
a r t i c l e
i n f o
Article history: Received 29 July 2014 Accepted 5 September 2014 Available online xxxx Keywords: total arthroplasty varus knee gap balancing pie-crusting technique cadaver biomechanical study
a b s t r a c t Balancing a varus knee is traditionally accomplished by releasing the medial soft-tissue sleeve off the tibia. Recently, “pie-crusting” (PC) medial structures has been described. In a biomechanical cadaver study we compared PC to traditional release (TR) to determine their effects on flexion and extension gaps. PC was done in five specimens along the anterior half of the medial soft-tissue sleeve and five along the posterior half, followed by a traditional release. In 90° flexion, valgus laxity after TR was significantly greater than after PC alone. PC of the anterior or posterior aspect of the medial soft-tissue sleeve can effect changes more in flexion than in extension, respectively. Complete TR did not provide more gap opening than PC in extension, but produced more effect in flexion. © 2014 Elsevier Inc. All rights reserved.
Soft-tissue or gap balancing is an important part of total knee arthroplasty (TKA) surgery, especially in osteoarthritic knees with varus deformity. Traditionally, balancing has been done by subperiosteally releasing portions of the medial soft-tissue sleeve off the proximal tibia [1–13], but this may lead to excessive laxity (especially when the posterior cruciate ligament is sacrificed) or residual pain about the area where the release was done [4,10,13–17]. A “pie-crusting” (PC) or “inside-out” technique has been described to balance the varus knee without compromising the structural integrity of the ligamentous structures and without subperiosteal (traditional) release [1,5,6,18–24]. Compared to isolated releases along the posterior aspect of the proximal tibia, releasing the anterior aspect of the medial softtissue sleeve may produce a larger increase in the joint gap in flexion than in extension [11,23]. Whiteside et al [11] compared the effects of a traditional release of the anterior portion of the medial collateral ligament (MCL) to the effects of release of the posterior aspect of the MCL and the posterior oblique ligament and found that anterior release had a greater effect on the flexion gap while the posterior release affected mainly the extension gap.
All research for this study took place at the University of Tennessee-Campbell Clinic Dept. of Orthopaedic Surgery & Biomedical Engineering. Each author certifies that he has no commercial associations (eg, consultancies, stock ownership, equity interest, patent/licensing arrangements, etc.) that might pose a conflict of interest in connection with the submitted article. The Conflict of Interest statement associated with this article can be found at http:// dx.doi.org/10.1016/j.arth.2014.09.005. Reprint requests: William M. Mihalko, MD, PhD, University of Tennessee-Campbell Clinic Department of Orthopaedic Surgery & Biomedical, Engineering, 1211 Union Avenue, Suite 510, Memphis TN 38104.
If pie-crusting techniques on the medial side of the knee can obtain equal effects in flexion and extension, there would be obvious advantages over complete ligament release. The purposes of this study were to determine what parts of the medial soft-tissue sleeve affect the gap in flexion or extension and to compare the results of pie-crusting to an additional standard medial release [4]. Our hypothesis was that pie crusting would be as effective as a traditional subperiosteal release and that targeting the anterior and posterior aspects of the medial soft-tissue sleeve would have more effect on the flexion and extension gaps, respectively. Material and Methods The specimens used in this study were lower extremities from fresh cadavers of donors who had undergone a previous primary TKA (Medical Education and Research Institute, Memphis, TN, and Restore Life USA, Johnson City, TN). IRB approval was obtained before beginning the study. Fourteen knee specimens (5 left and 9 right) were retrieved and all skin, subcutaneous tissue, and muscle were removed, while all aspects of the knee capsule and surrounding ligaments were carefully retained. Each specimen underwent fluoroscopic imaging to confirm no signs of aseptic loosening or bearing wear was present. The femur and tibia were cut transversely 180 mm proximal and distal to the knee joint line, the proximal tibio-fibular joint was left intact, and the fibular shaft was transected 100 mm from the joint line. The femur and tibia of each specimen were potted with urethane epoxy (Goldenwest MFG Inc, Cedar Ridge, CA) in a coupling that allowed mounting into a custom knee testing machine that has been validated in previous studies (Fig. 1) [11,17,23]. Specimens were placed with the tibia mounted
http://dx.doi.org/10.1016/j.arth.2014.09.005 0883-5403/© 2014 Elsevier Inc. All rights reserved.
Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005
2
W.M. Mihalko et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
Fig. 2. An example of the pie crusting performed on the SMCL of a right TKA specimen with the 11 blade in a checkerboard type pattern of 3–4 mm.
determine rotational laxity. Paired t-tests with a Holms–Sidak correction were used to determine statistical significance between tests. A corrected P-value was then calculated based on the number of comparisons between groups to determine overall statistically significant differences between groups. Fig. 1. One of the cadaveric specimens prepared and mounted into the custom knee testing machine. The machine allows for adjustment to place each specimen in its anatomic position with the epicondylar axis aligned with the femoral attached cross head.
vertically in the machine and the femoral coupling locked in a neutral position as defined by the vertically placed tibia. Specimens were tested with the knee joint at full extension and at 30, 60, and 90 degrees of flexion. An applied body weight force of 30 N was placed under the tibia to maintain joint contact during all tests. At each flexion angle, a 1.5-Nm internal and external rotational torque was applied about the tibial axis while the femur was fixed and the tibia was free to rotate about the joint center in the coronal plane. A 10-Nm varus and valgus torque also was applied to each specimen on the tibia, while internal– external rotation was unconstrained. Each test was performed three times initially to pre-condition each specimen with the third iteration utilized for each testing condition. A fellowship-trained, board-certified orthopedic surgeon then performed a standard medial parapatellar arthrotomy to gain access into the knee capsule. With a number 11 scalpel, alternating 3- to 4-mm stab incisions were made on the anterior aspect of the superficial medial collateral ligament (SMCL) from the medial epicondyle to the tibial insertion on 7 specimens (Fig. 2). The same procedure was done on the posterior aspect of the SMCL in the other 7 specimens. Each specimen was randomly assigned into one of the groups. Pie crusting was then done on the opposite portion of the SMCL and medial soft-tissue structures on all specimens, resulting in a “complete” PC technique. The medial soft-tissue sleeve was then released from its attachment on the proximal tibia from the joint line to a point 5 cm distally. After each step of the procedure, testing was done with the same loads and positions as the native TKA specimen. The angular deflection in degrees at ± 10 Nm of valgus torque in the coronal plane referenced from normal neutral position was recorded to determine the valgus laxity for each test. Likewise, the deflection in degrees at ± 1.5 Nm internal and external torque in the transverse plane referenced from the normal neutral position was recorded to
Results No significant changes in varus laxity from normal TKA knees were found when the surgical procedures were compared. Posterior piecrusting had a greater effect on valgus laxity at all flexion angles than did anterior pie-crusting. Anterior pie-crusting increased valgus laxity by 1.0 ± 0.2 degrees in full extension and 1.4 ± 0.6 degrees at 90 degrees of flexion. In comparison, posterior pie-crusting increased valgus laxity by 3.1 ± 1.2 degrees in extension and 3.0 ± 1.0 degrees in flexion. Complete pie-crusting and a traditional ligament release produced essentially the same changes (0.1 degree difference) in valgus laxity at full extension, but the traditional ligament release had a significantly greater effect at 60 and 90 degrees of flexion, increasing laxity by 1.4 and 2.5 degrees over pie-crusting, respectively (Fig. 3). No significant differences were found between pie crusting and ligament release in external rotation (Fig. 4A), but the difference was significant at all flexion angles in internal rotation when traditional release was compared to all of the pie-crusting release groups tested (Fig. 4B). Anterior pie-crusting had a greater effect on rotational laxity in flexion than extension, increasing internal and external laxity by 2.8 ± 0.4 and 2.7 ± 0.9 degrees, respectively, at 90 degrees of flexion. In comparison, internal and external laxity increased by 0.9 ± 0.3 and 0.14 ± 0.2 degrees in extension. Discussion As with previously reported studies concerning traditional release of the anterior and posterior portions of the MCL and posterior oblique ligament [11,25,26], anterior PC produced a greater change in laxity from normal conditions in flexion compared to full extension [25]. Likewise, PC of the posterior aspect of the medial soft-tissue sleeve (SMCL and posterior oblique ligament) produced greater laxity changes at full extension and 30 degrees of flexion, where these structures are most supportive. Overall, PC and ligament release produced increasingly greater changes in laxity as the flexion angle increased, but the traditional release did effect a greater overall change in flexion, with no difference in
Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005
W.M. Mihalko et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
3
Fig. 3. Valgus laxity changes for each surgical technique group tested. The bar graphs represent the means and standard error measures for each surgical technique group tested as compared to the native TKA specimen.
full extension. This suggests that while a traditional complete ligament release may compromise stability in flexion, PC may effect symmetric changes in the extension and flexion gaps. With severe varus deformity, however, PC may not provide enough release to balance the medial
joint gap. Our study showed that a traditional release can be added after PC to effect more change in flexion and full extension. Menghini et al [22] compared the biomechanical stiffness and failure mechanisms of pie-crusting to those of traditional release of the MCL in
Fig. 4. External (A) and internal (B) rotational laxity changes for each surgical technique group tested. The bar graphs represent the means and standard error measures for each surgical technique group tested as compared to the native TKA specimen.
Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005
4
W.M. Mihalko et al. / The Journal of Arthroplasty xxx (2014) xxx–xxx
18 fresh-frozen cadaver specimen pairs. They reported that the piecrusted MCLs had a lower stiffness than those with a traditional release, but the difference was not statistically significant. The pie-crusted MCLs failed at the joint line with a tearing type of failure while the traditionally released MCLs failed at the tibial insertion of the MCL. In our study, no specimen failed under the moments that were used. Menghini et al tested only the MCL without supporting ligaments, while we tested the entire soft-tissue sleeve, which included the anterior portions of the joint capsule, MCL, posterior oblique ligament, and posteromedial capsule including portions of the semimembranosus tendon insertion. Our purpose was to determine how pie-crusting would affect the medial joint gap from full extension to 90 degrees of flexion using the anterior and/or posterior or full medial soft tissue sleeve. Whiteside et al [11] tested a traditional release technique targeting the anterior or posterior half of the medial soft-tissue sleeve using the same knee testing machine as our study and found that anterior release had a greater effect on the flexion gap while the posterior release affected mainly the extension gap. Our results were similar except that the PC technique produced lower valgus deflection change when the anterior or the posterior halves were targeted, but when a traditional release was added there were similar overall values. In internal rotation the largest recorded changes were with the traditional release, while PC effected significantly smaller changes compared to normal. If rotational laxity is far greater with a traditional release than with a PC technique, this may have a meaningful effect on stability of the TKA during the postoperative rehabilitation period. Whether these changes are clinically significant, however, still remains in question. Limitations of this study include the small sample size and variations in the patient age and implant type, leading to large differences in normal laxity among the specimens. Further, we used specimens that already had a functioning TKA in place for over 10 years and did not have a contracted medial soft-tissue sleeve. While it is safe to assume that these specimens underwent some type of soft tissue balancing during initial TKA surgery, each specimen was used as its own control, so only changes from the normal functioning state are presented here. It should also be noted that we are comparing changes in coronal laxity within each specimen where variations in the condylar and polyethylene conformity afford the least amount of constraint (i.e. differences in implant conformity effects the AP and transverse plane stability more than coronal plane stability). Pie-crusting also was done with an “outside-in” rather than an “inside-out” technique because of the presence of the implants. Another limitation is the fact that the specimens had implants from different manufacturer in place. While this would not affect coronal plane deflections, transverse plane laxity measures might have been affected by the varying amounts of conformity of the different implant designs (7 posterior-stabilized designs and 7 cruciate-retaining designs). Two specimens had functioning posterior cruciate ligaments (PCL) in place. Because the PCL acts as a secondary coronal plane stabilizer [27], this could have caused variations in coronal plane laxity measures, but the fact that each specimen was compared to its own intact status should have minimized these effects. Despite these limitations, this study clearly showed that a PC technique that targets the anterior aspect of the medial soft-tissue sleeve can effect a change in flexion with minimal change in extension, while PC of the posterior half of the medial soft-tissue sleeve can effect a significant change in extension as well as flexion. Pie-crusting of the entire softtissue sleeve also may have an advantage in that it effectively changes the flexion and extension gap in a more symmetrical manner than an additional traditional release. If a larger medial gap is still needed in flexion, releasing the MCL would be a viable approach after pie-crusting.
Acknowledgments The authors wish to thank Kay Daugherty the Campbell Foundation Medical Editor for her aid in preparing this manuscript. No grant funding was utilized for this study.
References 1. Bellemans J. Multiple needle puncturing: balancing the varus knee. Orthopedics 2011;34:e510. 2. Koh HS, In Y. Semimembranosus release as the second step of soft tissue balancing in varus total knee arthroplasty. J Arthroplasty 2013;28:273. 3. Lee BS, Lee SJ, Kim JM, et al. No impact of severe varus deformity on clinical outcome after posterior stabilized total knee arthroplasty. Knee Surg Sports Traumatol Arthrosc 2011;19:960. 4. Matsueda M, Gengerke TR, Murphy M, et al. Soft tissue release in total knee arthroplasty. Cadaver study using knees without deformities. Clin Orthop Relat Res 1999;366:264. 5. Matsumoto T, Muratsu H, Kubo S, et al. Intraoperative soft tissue balance reflects minimum 5-year midterm outcomes in cruciate-retaining and posterior-stabilized total knee arthroplasty. J Arthroplasty 2012;27:1723. 6. Meftah M, Blum YC, Raja D, et al. Correcting fixed varus deformity with flexion contracture during total knee arthroplasty: the “inside-out” technique: AAOS exhibit selection. J Bone Joint Surg Am 2012;94:e66. 7. Mullaji A, Sharma A, Marawar S, et al. Quantification of effect of sequential posteromedial release on flexion and extension gaps: a computer-assisted study in cadaveric knees. J Arthroplasty 2009;24:795. 8. Picard F, Deakin AH, Clarke IV, et al. A quantitative method of effective soft tissue management for varus knees in total knee replacement surgery using navigational techniques. Proc Inst Mech Eng H 2007;221:763. 9. Verdonk PC, Pernin J, Pinaroli A, et al. Soft tissue balancing in varus total knee arthroplasty: an algorithmic approach. Knee Surg Sports Traumatol Arthrosc 2009; 17:660. 10. Whiteside LA, Mihalko WM. Surgical procedure for flexion contracture and recurvatum in total knee arthroplasty. Clin Orthop Relat Res 2002;404:189. 11. Whiteside LA, Saeki K, Mihalko WM. Functional medial ligament balancing in total knee arthroplasty. Clin Orthop Relat Res 2000;380:45. 12. Winemaker MJ. Perfect balance in total knee arthroplasty: the elusive compromise. J Arthroplasty 2002;17:2. 13. Yagishita K, Muneta T, Ikeda H. Step-by-step measurements of soft tissue balancing during total knee arthroplasty for patients with varus knees. J Arthroplasty 2003; 18:313. 14. Krackow KA, Mihalko WM. Flexion-extension joint changes after lateral structure release for valgus deformity correction in total knee arthroplasty. J Arthroplasty 1999;14:994. 15. Krackow KA, Mihalko WM. The effect of medial release on flexion and extension gaps in cadaveric knees: implications for soft-tissue balancing in total knee arthroplasty. Am J Knee Surg 1999;12:222. 16. Mihalko WM, Saleh KJ, Krackow KA, et al. Soft-tissue balancing during total knee arthroplasty in the varus knee. J Am Acad Orthop Surg 2009;17:766. 17. Saeki K, Mihalko WM, Patel V, et al. Stability after medial collateral ligament release in total knee arthroplasty. Clin Orthop Relat Res 2001;392:184. 18. Aglietti P, Lup D, Cuomo P, et al. Total knee arthroplasty using a pie-crusting technique for valgus deformity. Clin Orthop Relat Res 2007;464:73. 19. Bellemans J, Vandenneucker H, Van Lauwe J, et al. A new surgical technique for medial collateral ligament balancing: multiple needle puncturing. J Arthroplasty 2010;25:1151. 20. Clarke HD, Fuchs R, Scuderi GR, et al. Clinical results in valgus total knee arthroplasty with the “pie crust” technique of lateral soft tissue releases. J Arthroplasty 2005;20:1010. 21. Elkus M, Ranawat CS, Rasquinha VJ, et al. Total knee arthroplasty for severe valgus deformity. Five to fourteen-year follow-up. J Bone Joint Surg Am 2004;86:2671. 22. Meneghini RM, Daluga AT, Sturgis LA, et al. Is the pie-crusting technique safe for MCL release in varus deformity correction in total knee arthroplasty? J Arthroplasty 2013; 28:1306. 23. Mihalko WM, Krackow KA. Anatomic and biomechanical aspects of pie crusting posterolateral structures for valgus deformity correction in total knee arthroplasty: a cadaveric study. J Arthroplasty 2000;15:347. 24. Ranawat AS, Ranawat CS, Elkus M, et al. Total knee arthroplasty for severe valgus deformity. J Bone Joint Surg Am 2005;87(Suppl 1(Pt 2)):271. 25. Mihalko WM, Whiteside LA, Krackow KA. Comparison of ligament-balancing techniques during total knee arthroplasty. J Bone Joint Surg Am 2003;85(Suppl 4):132. 26. Mihalko WM, Whiteside LA. Bone resection and ligament treatment for flexion contracture in knee arthroplasty. Clin Orthop Relat Res 2003;406:141. 27. Mihalko WM, Miller C, Krackow KA. Total knee arthroplasty ligament balancing and gap kinematics with posterior cruciate ligament retention and sacrifice. Am J Orthop (Belle Mead NJ) 2000;29:610.
Please cite this article as: Mihalko WM, et al, Biomechanical Validation of Medial Pie-Crusting for Soft-Tissue Balancing in Knee Arthroplasty, J Arthroplasty (2014), http://dx.doi.org/10.1016/j.arth.2014.09.005
