Increased‐congruency bearing options are widely available in numerous total knee replacement (TKR) systems, with the intended purpose of compensating for posterior‐cruciate ligament (PCL) deficiency. However, their ability to provide adequate stability in this setting has been debated. This in vitro joint simulator study measured changes in knee joint kinematics and stability during passive flexion–extension motions and simulated activities of daily living resulting from TKR with condylar‐stabilized (CS) TKR without a PCL versus cruciate‐retaining (CR) TKR. During passive flexion, the CS TKR resulted in a more posterior tibial positioning than both the intact joint and CR TKR (by 3.4 ± 1.0 mm and 4.8 ± 0.7 mm, respectively). With a posterior tibial force applied, the CS TKR tibia was again significantly more posterior than that of the intact joint and CR TKR (by 4.7 ± 1.3 mm and 5.6 ± 0.8 mm, respectively). Furthermore, there were significant differences in the anterior/posterior kinematics of both TKR with respect to intact knees during gait, and differences between the CS and CR TKR during stair ascent and descent. Overall, there appears to be a reduction in anterior–posterior stability of the PCL‐deficient CS TKR knee, suggesting that contemporary increased‐congruency bearing surface designs may not adequately compensate for the loss of the PCL. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2172–2181, 2019

PurposeVarious reconstruction techniques have been employed to restore normal kinematics to PCL‐deficient knees; however, studies show that failure rates are still high. Damage to secondary ligamentous stabilizers of the joint, which commonly occurs concurrently with PCL injuries, may contribute to these failures. The main objective of this study was to quantify the biomechanical contributions of the deep medial collateral ligament (dMCL) and posterior oblique ligament (POL) in stabilizing the PCL‐deficient knee, using a joint motion simulator. MethodsEight cadaveric knees underwent biomechanical analysis of posteromedial stability and rotatory laxity using an AMTI VIVO joint motion simulator. Combined posterior force (100 N) and internal torque (5 Nm) loads, followed by pure internal/external torques (± 5 Nm), were applied at 0, 30, 60 and 90° of flexion. The specimens were tested in the intact state, followed by sequential sectioning of the PCL, dMCL, POL and sMCL. The order of sectioning of the dMCL and POL was randomized, providing n = 4 for each cutting sequence. Changes in posteromedial displacements and rotatory laxities were measured, as were the biomechanical contributions of the dMCL, POL and sMCL in resisting these loads in a PCL‐deficient knee. ResultsOverall, it was observed that POL transection caused increased posteromedial displacements and internal rotations in extension, whereas dMCL transection had less of an effect in extension and more of an effect in flexion. Although statistically significant differences were identified during most loading scenarios, the increases in posteromedial displacements and rotatory laxity due to transection of the POL or dMCL were usually small. However, when internal torque was applied to the PCL‐deficient knee, the combined torque contributions of the dMCL and POL towards resisting rotation was similar to that of the sMCL. ConclusionThe dMCL and POL are both important secondary stabilizers to posteromedial translation in the PCL‐deficient knee, with alternating roles depending on flexion angle. Thus, in a PCL‐deficient knee, concomitant injuries to either the POL or dMCL should be addressed with the aim of reducing the risk of PCL reconstruction failure.

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Objectives: Approximately 95% of PCL injuries are multi-ligament injuries, yet it remains unclear if simultaneous injuries sustained to medial-side knee stabilizers such as the posterior oblique ligament (POL) and deep medial collateral ligament (dMCL) also need to be addressed. Pathomechanical kinematics that still exists after PCL reconstructions may be the result of residual instability due to deficiency of these secondary stabilizers. The objective of this study is to characterize the relative contributions of the POL, dMCL and superficial medial collateral ligament (sMCL) in PCL-deficient knees. We hypothesize that the POL would contribute to stability in extension only, whereas the dMCL would provide stability throughout the entire flexion range of motion. Methods: Eight specimens (aged 40-63, 5 female, 1 male, 2 pairs) were potted and the PCL was dissected arthroscopically. Each specimen was mounted onto a VIVO joint motion simulator (AMTI) and flexed from 0 to 90 degrees with a 10 N compressive load applied along the long axis of the tibia. During this motion, a 5 Nm internal or external moment was applied to the tibia, and the resulting kinematics were recorded. Recorded kinematics were applied back on the specimen, while the joint’s reaction torque to this rotation was measured. The decrease in reaction torque was measured following randomized dissection of the POL and dMCL (4 POL first and 4 dMCL first); the sMCL was always dissected last. The contribution of each ligament to this reaction torque was measured by calculating the change in the reaction torque caused by the ligament’s dissection at 0, 30, 60 and 90 degrees. Each ligament’s relative contribution was compared to the net reaction torque of the joint to calculate the percentage contribution of the ligament. The contribution of each ligament was analyzed using a one-way repeated measure ANOVA with a significance value of 0.05. Results: With an internal torque applied, the dMCL’s contribution to the reaction torque was greatest at 30 degrees, accounting for up to 23% +/- 19% of the overall reaction torque; its contribution was not significantly affected by flexion angle (p>0.05). The POL’s contribution was significantly affected by flexion angle (p=0.007), accounting for 40% +/- 15% of the reaction torque at 0 degrees but only 6% +/- 4% at 90 degrees. The sMCL’s contribution was also sensitive to flexion angle (p=0.006), accounting for 14% ± 16% of the reaction torque at 0 degrees and increasing to 28% +/- 12% at 90 degrees. With an external torque applied, the dMCL’s contribution accounted for 12% +/- 4% of the reaction torque at 0°, but this decreased to 4% +/- 2% at 90 degrees; its contribution was significantly affected by flexion angle (p=0.038). The POL’s contribution accounted for 12% +/- 3% of the reaction torque at 0 degrees and 3% +/- 3% at 90 degrees and the flexion angle changed this contribution significantly (p=0.003). A large portion of the reaction torque was provided by the sMCL, accounting for 52% +/- 7% at 90 degrees. Conclusions: Our results show that, with internal torques applied to the tibia, the POL plays an important role in resisting motion when the joint is near full extension. Conversely, the dMCL’s (and sMCL’s) contribution is largest in flexion. Neither the POL nor dMCL have a large contribution towards resisting external tibial torques; the sMCL seems to be the primary ligament resisting external rotation among medial ligaments. Thus, there is the potential for increased posteromedial instability if POL and dMCL injuries are not addressed, increasing the risk of a failed PCL reconstruction.