Cartilage atrophy in the knees of patients after seven weeks of partial load bearing

Objective. It is currently unknown whether human cartilage properties change during short periods of partial load bearing. We used a post-ankle fracture model to explore whether changes in cartilage morphology occur in the knee under conditions of partial load bearing. Methods. The knees of 20 patients with Weber type B and type C fractures were examined using magnetic resonance imaging. The first scan was obtained shortly (mean +/- SD 3.2 +/- 3.0 days) after the injury, and a second scan was obtained 7 weeks later (mean +/- SD 50.7 +/- 5.5 days). The morphology (mean and maximum thickness, volume, and surface area) of the patellar, tibial, and femoral cartilage was determined from coronal and axial magnetic resonance images (fat-suppressed gradient-echo). Results. Between week 0 and week 7, the cross-sectional area of the quadriceps muscle was reduced by 11% (P < 0.001). Changes in the mean ( +/- SD) cartilage thickness ranged from -2.9 +/- 3.2% in the patella to -6.6 +/- 4.9% in the medial tibia. No significant change in cartilage morphology of the contralateral knee was observed. Conclusion. Results of this study demonstrate that in a post-ankle fracture model of partial load bearing, cartilage morphology in all knee compartments is subject to significant change. Changes in the femorotibial joint exceeded those in the patella, whereas no change was observed in the contralateral knee. These findings raise the question of whether cartilage is mechanically less competent and particularly vulnerable after states of partial or complete immobilization.