In vitro biomechanical evaluation of tri-condylar total knee arthroplasty with posterior release for restoration of full extension

BACKGROUND/OBJECTIVE: The continuous improvement of knee function during deep flexion remains a challenge in total knee arthroplasty. Tri-condylar total knee arthroplasty has been designed to achieve this goal. However, the introduction of a third nonanatomic spherical condyle might prevent the joint from reaching full extension due to posterior soft tissue tightening. This study aimed to address these issues related to soft tissue tightening and full extension limitation. METHODS: Biomechanical tests were performed on six cadaveric specimens of the entire lower extremities. The tri-condylar design was compared with a posterior cruciate sacrificing design of the same shape without the ball structure. Knee joint kinematics was measured, including the extension and flexion angles, the extension balance, and the extension gap. The test was repeated after release of the medial and lateral posterior intercondylar soft tissues at a safe distance from the popliteal artery and nerves. RESULTS: Both designs resulted in a knee flexion angle up to ∼130°. The tri-condylar design showed an extension angle of –11.2 ± 5.4°, which was a significantly greater limitation than that obtained with the cruciate sacrificing design (–3.8 ± 4.7°; p = 0.047). Moreover, the extension angle of the tri-condylar design was significantly improved after the release of posterior intercondylar soft tissues (–0.1 ± 6.7°; p = 0.028). CONCLUSION: The tri-condylar design efficiently allowed the full extension by the release of posterior intercondylar soft tissues at a safe distance from the popliteal artery and nerves.