Tibio-femoral movement in the living knee. A study of weight bearing and non-weight bearing knee kinematics using ‘interventional’ MRI

Abstract

The aim of this study was to image tibio-femoral movement during flexion in the living knee. Ten loaded male Caucasian knees were initially studied using MRI, and the relative tibio-femoral motions, through the full flexion arc in neutral tibial rotation, were measured. On knee flexion from hyperextension to 120°, the lateral femoral condyle moved posteriorly 22 mm. From 120° to full squatting there was another 10 mm of posterior translation, with the lateral femoral condyle appearing almost to sublux posteriorly. The medial femoral condyle demonstrated minimal posterior translation until 120°. Thereafter, it moved 9 mm posteriorly to lie on the superior surface of the medial meniscal posterior horn. Thus, during flexion of the knee to 120°, the femur rotated externally through an angle of 20°. However, on flexion beyond 120°, both femoral condyles moved posteriorly to a similar degree. The second part of this study investigated the effect of gender, side, load and longitudinal rotation. The pattern of relative tibio-femoral movement during knee flexion appears to be independent of gender and side. Femoral external rotation (or tibial internal rotation) occurs with knee flexion under loaded and unloaded conditions, but the magnitude of rotation is greater and occurs earlier on weight bearing. With flexion plus tibial internal rotation, the pattern of movement follows that in neutral. With flexion in tibial external rotation, the lateral femoral condyle adopts a more anterior position relative to the tibia and, particularly in the non-weight bearing knee, much of the femoral external rotation that occurs with flexion is reversed.

Introduction

There has already been extensive work on the kinematics of the tibio-femoral joint, but no previous study has imaged the internal anatomy of the living weight-bearing knee throughout the range of movement. Recent work using MRI in unloaded cadaveric and living knees has permitted descriptions of the femoral and tibial articular surfaces, and has imaged the movements of the medial and lateral femoral condyles during various arcs of knee flexion (Niitsu et al., 1990; Ando et al., 1994; Todo et al., 1999; Iwaki et al., 2000; Pinskerova et al., 2000; Hill et al., 2000; Nakagawa et al., 2000; Wretenberg et al., 2002). The validity of this method of employing MRI to study tibio-femoral movement has been confirmed by comparing it with RSA (Karrholm, 2000), RSA combined with CT and with a 3D digitiser (Martelli and Pinskerova, 2002; McPherson et al. (2002), McPherson et al. (2004)) carried out on the same 3 cadaveric knees.

A preliminary study to test the feasibility of using open MRI to image the weight-bearing living knee was published in Hill et al. (2000). Only 7 knees in male subjects were imaged in 4 positions from 0° to 90°. Non-weight bearing images were also obtained but not in the same subjects. Thus feasibility was demonstrated but the data was limited. The results obtained were comparable to the cadaveric experience (Iwaki et al., 2000). The object of the present study was to provide a definitive description over the whole flexion range based on Hill et al.'s preliminary work. We sought data points every 10° flexion from full extension to full flexion weight-bearing in 10 males. We also extended data on the effect of non-weight bearing vs. weight-bearing and of tibial rotation, and we compared males with females and left with right knees.