Medial unicompartmental knee arthroplasty in ACL-deficient knees is a viable treatment option: in vivo kinematic evaluation using a moving fluoroscope

Abstract

Purpose Unicompartmental knee arthroplasty (UKA), resulting in similar kinematics to native knees, is functionally superior to total knee arthroplasty (TKA). However, ACL deficiency is generally considered to be a contraindication. The main purpose of this study was to investigate if UKA in ACL‐deficient knees would result in similar kinematics to conventional UKA with an intact ACL. Methods Ten conventional UKA patients were compared to eight ACL‐deficient patients with a reduced tibial slope to compensate for instability, resulting from the deficient ACL. Knee kinematics was evaluated with a moving fluoroscope, tracking the knee joint during daily activities. In a standing position (baseline), posterior shift of the femur was observed for ACL‐deficient UKA patients, compared to conventional UKA patients. Results A significant posterior femoral shift in the ACL‐deficient group was observed during the first 25% (near extension) of deep knee bend, while there was no difference in kinematic waveforms for all other activities. No significant range of motion differences across different activities between the two UKA groups were detected, except for an increase of medial AP translation in the ACL‐deficient group, during deep knee bend and stair descent. Conclusion Despite the posterior femoral shift due to ACL deficiency, both UKA groups showed similar kinematic waveforms, indicating that posterior tibial slope reduction can partially compensate for ACL function. This supported our hypothesis that fixed bearing UKA can be a viable treatment option for selected ACL‐deficient patients, allowing patient‐specific kinematics. While anteroposterior laxity can be compensated, rotational stability was a prerequisite for this approach. Level of evidence III.

Computational analysis of tibial slope adjustment with fixed-bearing medial unicompartmental knee arthroplasty in ACL- and PCL-deficient models

“…Previous studies have proved that the posterior tibial slope is important for accurate knee arthroplasty. 35,36,38 A previous study by Kang et al 39 indicated that posterior TF translation significantly increased as posterior tibial slope increased. The translation of posterior TF is crucial in knee arthroplasty, as a higher degree of flexion is allowed before a TF impingement occurs.…”

“…Similar trends have been found in various biomechanical studies. 4,12,38 A previous study showed that anterior tibial translations during the Lachman test decreased by approximately 5 mm with an 8° posterior tibial slope. 4 However, no variation in slope altered the pivot shift kinematics in ACL-deficient knees.…”

More Anterior in vivo Contact Position in Patients With Fixed-Bearing Unicompartmental Knee Arthroplasty During Daily Activities Than in vitro Wear Simulator

“…Accurate in vivo 6-DOF knee kinematics and articular contact behavior of the knee arthroplasty during functional activities are crucial factors to predict its biotribology and PE wear. However, only partial kinematic parameters of FB UKA have been reported, which is not sufficient in in vitro wear simulation ( Mochizuki et al, 2013 ; Zumbrunn et al, 2020 ). In the current study, the specific in vivo 6-DOF showed different patterns between the stance phase during gait and weight-bearing knee flexion–extension (single-leg lunge and sit-to-stand) for the knee following FB UKA.…”

“…The precise and detailed knee kinematics and kinetics of UKA during weight-bearing daily activities can give significant insights into the in vitro UKA simulator’s loading condition when evaluating its wear performance. The knee flexion, tibial internal rotation, and femoral anteroposterior movement of FB UKA during several activities have been reported ( Mochizuki et al, 2013 ; Zumbrunn et al, 2020 ). However, other kinematic parameters were not reported, e.g., knee abduction-adduction; and more demanding daily activities should be investigated.…”

Patient-specific musculoskeletal models as a framework for comparing ACL function in unicompartmental versus bicruciate retaining arthroplasty

“…These results indicate the importance of implant designs in preserving normal knee kinematics in both UKA and TKA. 24,44,45 With regards to role of ACL, Zumbrunn et al 46 compared 10 conventional UKA patients with eight ACL-deficient UKA patients using a moving fluoroscope system, and found that similar kinematic waveforms were seen in both UKA groups, but ACL-deficient group shows a significant posterior femoral shift during the first 25% of deep knee bend. Suggs et al 9 showed that functional ACL is likely needed for increasing odds of long-term success after medial UKA.…”