Objective. A previous cross-sectional study indicated that the morphology of patellar and tibial cartilage is subject to change after spinal cord injury (SCI). The aim of this study was to perform a longitudinal analysis of cartilage atrophy in all knee compartments, including the femoral condyles, in SCI patients over 12 months.Methods. The right knees of 9 patients with complete, traumatic SCI were examined shortly after the injury (mean ؎ SD 9 ؎ 4 weeks) and at 6 and 12 months postinjury. Three-dimensional morphology of the patellar, tibial, and femoral cartilage (mean and maximum thickness, volume, and surface area) was determined from coronal and transversal magnetic resonance images (fat-suppressed gradient-echo sequences) using validated postprocessing techniques.Results. The mean thickness of knee joint cartilage decreased significantly during the first 6 months after injury (range 5-7%; P < 0.05). The mean change at 12 months was 9% in the patella, 11% in the medial tibia, 11% in the medial femoral condyle, 13% in the lateral tibia, and 10% in the lateral femoral condyle (P < 0.05 for all compartments).Conclusion. This is the first report of a longitudinal analysis of cartilage atrophy in patients with SCI. These data show that human cartilage atrophies in the absence of normal joint loading and movement after SCI, with a rate of change that is higher than that observed in osteoarthritis (OA). A potential clinical implication is that cartilage thinning after SCI may affect the stress distribution in the joint and render it vulnerable to OA. Future studies should focus on whether specific exercise protocols and rehabilitation programs can prevent cartilage thinning.Integrity of the morphologic and mechanical properties of articular cartilage is a prerequisite for appropriate function of diarthrodial joints. As suggested by various animal studies, a certain amount of mechanical loading and movement of the joint is required in order to maintain normal cartilage morphology, biochemical composition, and biomechanical properties (1). However, the results of these animal studies have been highly variable and inconsistent. Jurvelin et al (2), for example, observed a 9% decrease in cartilage thickness in the canine knee after 11 weeks of rigid immobilization. Haapala et al (3) reported a large decrease (ϳ20%) in cartilage of the medial femur, but no changes in cartilage of the lateral tibia and lateral femur (4), of canine knee joints. In contrast, Leroux et al (5) found that a shorter period of nonrigid immobilization (4 weeks) did not change the knee cartilage thickness of the dogs in their study.Spinal cord injury (SCI) causes unloading and restricted movement of the lower limb joints for substantial periods of time. As a consequence, patients with SCI encounter secondary complications, such as decreases in muscle mass, cardiovascular fitness, and bone density (6,7). Radiographic evidence of narrowing of the hip joint space by more than 50% in 25 of 200 patients with flaccid paralysis was identified in one st...