Knee kinematics after lateral UKA are closer to native knee kinematics compared to those after medial UKA, a cadaveric study
ESSKA Academy. Wada K. May 12, 2018; 218106
Keizo Wada
Keizo Wada
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Objectives: Several previous studies have shown better functional outcomes after unicompartmental knee arthroplasty (UKA) than after total knee arthroplasty (TKA). This could partially be explained by the fact that the kinematics of UKA is better than those of TKA. Several kinematic studies of UKA have been reported, although whether UKA can restore the kinematics of the native knee has been controversial and there have been few reports on the kinematics of lateral UKA. The aim of this study was to compare the intraoperative kinematics of medial and lateral UKA with those of the native knee using a navigation system.

Methods: Six fresh-frozen cadaveric knees were used in the study. Medial UKA was performed in each right knee and lateral UKA was performed in each left knee. All UKA procedures were assisted by a navigation system. The tibial internal rotation angle and coronal alignment of the mechanical axis during passive knee flexion were assessed to evaluate intraoperative knee kinematics before and after surgery using the navigation system at maximum extension, at 10º intervals from 0º to 120° flexion, and at maximum flexion during passive knee motion. The Mann-Whitney U test was used to evaluate differences in the rotation angle of the tibia and the coronal alignment of the mechanical axis at each knee flexion angle between the native knee and the UKA knee.

Results: The rotation angles of the tibia in early flexion phase of medial UKA were significantly larger than those of native knees, indicating that the screw home movement was impaired after medial UKA. On the other hand, lateral UKA produced rotational kinematics close to those of the native knee throughout knee flexion. There were no significant differences in coronal alignment of the mechanical axis at each angle of knee flexion between native and UKA knees.

Conclusions: In present cadaveric study, rotational and varus/valgus kinematics after both medial and lateral UKA were similar to those of the native knee. However, the screw home movement of the native knee was not restored after medial UKA but was preserved after lateral UKA. Thus, the geometry of the medial tibial articular surface is a determinant of the screw home movement.

Navigation system, Unicompartmental knee arthroplasty, Screw home movement, Knee kinematics, Cadaveric study
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