WHAT IS LIMITING ULTIMATE MAXIMAL FLEXION IN PCL-RETAINING TKA?

Abstract

Introduction The purpose of this study was to detect the limiting mechanism of maximal active flexion that can ultimately be obtained by patients after PCL-retaining TKA.

Methods The study consisted of two parts. In the first part, 30 patients with well performing PCL-retaining TKAs were examined using videofluroscopy. In deep flexion, observations were directed towards potentiallly determinant factors of maximal obtainable flexion. Based upon these observations, a newly defined paramater, called the “posterior condylar offset”, was found to be important. The exact influence of this parameter was investigated in part two, in which 150 consecutive patients with PCL-retaining TKA were reviewed.

Results Aberrant kinematics were observed in the majority of cases. In 27 patients (93%) slide-forward of the femur was noted with flexion, with anterior translation of the medial and/or lateral femorotibial contact position. In deep squat, direct impingement of the posterior aspect of the tibial insert against the shaft of the femur was noted in 21 cases (72.4%), blocking further flexion. In part two of the sutdy, it was demonstrated that in knees with decreased post-operative “posterior condylar offset”, such impingement occurred faster and lead to decreased maximal obtainale flexion (p< 0.001).

Conclusions Maximal obtainable flexion is in the majority of cases determined by posterior tibial insertion impingement against the femoral bone and this occurs as a consequence of aberrant kinematics with anteiror sliding of the femur during flexion. Restoration of “posterior condylar offset” is important, since it allows greater degrees of flexion before impingement occurs.

In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits.