Longitudinal study of the relationship between knee angle and tibiofemoral cartilage volume in subjects with knee osteoarthritis.

OBJECTIVES There is emerging evidence that knee alignment is associated with progression of osteoarthritis (OA). The aim of this study was to examine the relationship between baseline knee angle and the rate of cartilage loss in subjects with knee OA. METHODS One hundred and seventeen subjects with knee OA had standing radiographs and MRI on their symptomatic knee at baseline and at the 1.9+/-0.2 yr follow-up. Knee cartilage volume was measured at baseline and follow-up. Knee angle was defined as the angle subtended by a line drawn through the mid-shaft of the femur with respect to one drawn through the mid-shaft of the tibia. RESULTS At baseline, in the medial compartment, as the angle decreased (i.e. was less varus) the tibial and femoral cartilage volume increased. In the lateral compartment, as the angle became more valgus, there was a reduction in tibial and femoral cartilage volume. In the longitudinal study, for every 1 degrees increase in baseline varus angulation there was an average annual loss of medial femoral cartilage of 17.7 micro l [95% confidence interval (CI) 6.5-28.8]. Although not statistically significant, there was a trend for a similar relationship between loss of medial tibial cartilage volume and baseline knee angle. In the lateral compartment, there was an average loss of tibial cartilage volume of 8.0 micro l (95% CI 0.0-16.0) for every 1 degrees increase in valgus angle. CONCLUSIONS Baseline knee angle is associated with the rate of cartilage loss in the knee. Further work will be needed to determine whether therapies aimed at modifying the knee angle will reduce the progression of knee OA.