Tibial and femoral cartilage changes in knee osteoarthritis

Background-Despite the increasing interest in using knee cartilage volume a s an outcome measure in studies of osteoarthritis (OA), it is unclear what components of knee cartilage will be most useful as markers of structure in the tibiofemoral (TF) joint. Objective-To compare the changes that occur in femoral and tibial cartilage volume in normal and osteoarthritic knees and how they relate to radiologi cal grade. Methods-82 subjects (44 female, 38 male, age range 35-69 years) with a spec trum of radiological knee OA were examined. Each subject had femoral and ti bial cartilage volume in the medial and lateral TF joint determined from T- 1 weighted fat saturated magnetic resonance images of the knee. Radiologica l grade of OA was determined from standing knee radiographs. Results-There was strong correlation between femoral and tibial cartilage v olume measured in both the medial (R=0.75, p <0.001) and lateral TF joint ( R=0.77, p <0.001). Similar correlations persisted when those with normal an d those with OA joints were examined separately at both the medial and late ral TF joint. For each increase in radiological grade of joint space narrow ing (0-3), there was a mean (SD) reduction in tibial cartilage volume of 1. 00 (0.32) ml in the medial compartment and 0.53 (0.25) ml in the lateral co mpartment, after adjusting for differences in bone size. Similar changes we re seen in the femoral cartilage. Conclusions-The amounts of tibial and femoral cartilage are strongly relate d. It may be that for TF joint disease, measuring tibial cartilage alone ma y be adequate, given that measurements of the total femoral cartilage are l ess reproducible and the difficulties inherent in identifying the most appr opriate component of femoral cartilage to measure.