| Part 1 Cadaveric study of the optimal isometric region of the anterolateral surface of the knee during passive motionObjective: To test the isometry of different areas of the anterolateral knee using the surgical isometric test and by optical instrument on cadaveric human knees and to determine the optimal isometric region of the anterolateral aspect of the knee as a reference for ALL reconstruction.Methods: Six fresh-frozen cadaveric human knees were used in this study.5 femoral reference points(A-E)were selected from the lateral femur,which were located in different areas relative to the lateral femoral epicondyle,and 3 tibial reference points,5 mm(T1),10mm(T2),and 15 mm(T3)below the joint line,halfway between the center of Gerdy’s tubercle and the fibula head were selected.At 0°,15°,30°,45°,60°,75°,and 90° of knee flexion,the change in length between each pair of reference points was measured using sutures.Then the data of the anterolateral surface of the knee was obtained using a threedimensional optical measurement system to create a three-dimensional model of the anterolateral surface.9 reference points were selected at each of the surfaces of the femur and tibia respectively,and the three-dimensional length change between each pair of tibial and femoral reference points was measured during passive knee flexion at 0°,15°,30°,45°,60°,75°,and 90°.Results: Of the 15 pairs of reference points measured manually using sutures,the mean maximum rates of length change for the point combinations corresponding to points A(posterior and proximal to the lateral femoral epicondyle)and E(over-the-top position)was less than 10%,which is considered as the maximum acceptable change rate for ligament reconstruction.However,the 95% CI for the mean maximum rate of length change for the A-T1 combination included 10%,which did not meet the requirements for ligament reconstruction.Among the 81 pairs of combined points measured using an optical measurement system,the mean maximum length change rate of three pairs of combined points,F2-Td,F2-Tg,and F3-Tb,were less than 10%,but only the 95% CI of the mean maximum length change rate of the F3(posterior and proximal to the lateral epicondyle of the femur)-Tb(proximal to the halfway between the center of Gerdy’s tubercle and the fibula head)did not include 10%.The length change rate between the combined points that met the criteria for ALL reconstruction tended to increase with increasing knee flexion angle while the absolute length tended to decrease.Conclusion: The combination of the posterior and proximal region to the lateral femoral epicondyle with the proximal region to halfway between the center of Gerdy’s tubercle and the fibula head is most isometric and can be considered as a reference region for femoral and tibial localization points in isometric ALL reconstruction.Part 2 Biomechanical study of anterior cruciate ligament combined with anterolateral ligament reconstructionObjective: To establish a model of anterolateral instability of the knee by sectioning the anterior cruciate ligament(ACL),anterolateral structures(ALS),and lateral meniscus posterior root(LMPR)to meet the indications for the ALL reconstruction.ACL reconstruction and ALL reconstruction were performed sequentially on this model to investigate the effect of combined ACL and ALL reconstruction with the synthetic ligament.Methods: In this study,six fresh-frozen cadaveric human knees were tested in the following four conditions using a 6-degree-of-freedom robot: intact,ACL+ALS+LMPRsectioned,ACL reconstruction,and ALL reconstruction.The following 3 test protocols were performed for each condition of the knees: the anterior displacement of the tibia under the89 N anterior force(anterior tibial translation,ATT)was measured at 0°,30°,60°,and 90°of passive knee flexion;the internal rotation(IR)of the tibia was measured at 0°,15°,30°,and 45° of passive knee flexion under 5N·m internal rotation torque;the simulated pivot shift test(5N·m internal rotation combined with 7N·m external rotation torque)was applied to the tibia,and the displacement of the lateral compartment and tibial internal rotation were measured at 0°,15°,30°,and 45° of passive knee flexion.Results: After sectioning ACL,ALS,and LPMR,the knee showed significant instability under each loading protocol(anterior force,internal rotation torque,and simulated pivot shift test)compared to the intact state(mean differences were 14.3 mm,2.5°,7.0 mm,and 2.6°,respectively;95% CI did not include 0).After ACL reconstruction,anterior stability was significantly restored compared to the injured state(mean difference is13.3 mm,95% CI did not include 0),but internal rotation stability,lateral compartment displacement and internal rotation under the simulated pivot shift test were not restored to the intact state(mean differences were 1.4°,4.2 mm,and 1.6° respectively;95% CI did not include 0).Internal rotation stability and lateral compartment displacement and internal rotation under the simulated pivot shift were significantly improved after ALL reconstruction compared with ACL reconstruction(mean differences were 2.3°,5.0 mm,and 2.3°,respectively;95% CI did not include 0),and no significant differences(mean differences were-0.8 °,-0.7mm and-0.7 respectively;95% CI did not include 0)was observed compared with the intact state.Conclusion: By simultaneously sectioning the ACL,ALS,and LMPR,we successfully established a model of anterolateral instability of the knee that meets the indications for ALL reconstruction surgery,which means after ACL reconstruction alone,anterolateral instability(elicited by persistent positive pivot shift test)still exists.The combined reconstruction of ACL and ALL with synthetic ligament showed good control of anterolateral instability of the knee,which could effectively reduce the occurrence of pivot shift phenomenon and restore the stability of the knee to the level of the intact state,without showing excessive restriction of normal activities. |
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