Mobile medial pivot (lateral slide) type total knee arthroplasty exhibits a medial pivot pattern: three-dimensional motion analysis using cadaveric knees

Abstract

Purpose The purpose of this study was to analyze the dynamic kinematics of the mobile medial pivot-type total knee arthroplasty (MMPTKA) using the three-dimensional (3D)-to-2D registration technique. Methods Cadaveric knees from five humans were used. Computed tomography of the lower limb and preoperative 3D planning for MMPTKA were performed. After performing TKA, passive motion of the knee was observed from a fully extended position to maximum flexion using a flat panel detector. The following parameters were determined: (1) anteroposterior (AP) translations of the medial and lateral most distal points (estimated contact point) of the femoral component, (2) rotational femoral component’s X-axis (FCX) angle, and (3) rotational insert angle. Paired t-tests were used to analyze differences in the AP translation between the medial and lateral most distal points of the femoral component as well as differences in the changes in the rotational angle between the FCX and X-axis of the insert on the tibial component’s axial plane. Results The AP translations of the femoral component’s medial and lateral most distal points were 8.4 ± 2.5 and 13.6 ± 3.3 mm, respectively (p = 0.001). The rotational angles of the FCX and insert were 10.7° ± 4.9° external rotation and 8.9° ± 4.1° internal rotation, respectively (p = 0.004). Conclusions The posterior translation of the lateral side of the femoral component was greater than that of the medial in all cases. Hence, a medial pivot pattern was identified. The femoral component exhibited external rotation throughout knee flexion in all subjects, whereas the mobile insert exhibited internal rotation (opposite pattern relative to the femoral component). This study provides valuable kinematical information of MMPTKA that has not been clear yet.

Mobile medial pivot (lateral slide)‐type total knee arthroplasty exhibited different motion patterns between under anaesthesia and weight‐bearing condition

“…The mobile insert exhibited little rotation or external rotation similar to that of the femoral component during knee flexion under the in vivo weight‐bearing condition during squatting, whereas the mobile insert exhibited internal rotation opposite to that of the femoral component during knee flexion under anaesthesia. This motion was similar to the results of the cadaveric study [24]. Regarding the femoral component, the amount of posterior translation of the medial and lateral sides under anaesthesia was greater than during squatting (i.e., in vivo weight‐bearing).…”

“…The movement of the axial rotation of the femoral component relative to the mobile‐bearing insert exhibited little rotation [28]. However, a previous cadaveric study using MMPTKA showed an opposite rotation of the insert relative to the femoral component and concluded that the shape of the inserts with high medial constraint and asymmetrical medial and lateral surfaces may be a major factor for this motion [24]. In this study, the insert showed opposite rotation relative to the femoral component under anaesthesia, as in the cadaveric study.…”

“…In a previous study, motion analysis of MMPTKA was performed using the three‐dimensional‐to‐two‐dimensional (3D‐to‐2D) registration technique on cadaveric knees [24]. The medial and lateral sides of the femoral component exhibited posterior translation of 8.4 and 13.6 mm, respectively, as the knee flexed, and cases with a greater magnitude of lateral posterior translation showed a medial pivot pattern.…”

“…Meanwhile, the insert exhibited a characteristic pattern of internal rotation relative to the tibial component throughout knee flexion. This internal rotation of the insert caused an overhang of the lateral side of the insert in the deep knee flexion phase, which raised concerns about the possibility of a similar phenomenon occurring in clinical use and any related implications for patient outcomes [24]. Therefore, in vivo motion analysis that considers soft tissue balance is necessary.…”