Effect of muscle contractions on cartilage: morphological and functional magnetic resonance imaging evaluation of the knee after spinal cord injury()

OBJECTIVE: To evaluate the effect of complete absence of muscle contractions on normal human cartilage in the presence of joint motion. METHODS: Patients with complete acute spinal cord injuries were enrolled. All patients underwent magnetic resonance imaging (MRI) on both knees as soon as their medical condition was stable and at six months after the primary lesion. All patients received rehabilitation treatment that included lower-limb passive motion exercises twice a day. The MRIs were analyzed by two radiologists with expertise in musculoskeletal disorders. A region of interest was established at the patellar facets and trochlea, and T2 relaxation times were calculated. The area under the cartilage T2 relaxation time curve was calculated and standardized. RESULTS: Fourteen patients with complete spinal cord injuries were enrolled, but only eight patients agreed to participate in the study and signed the informed consent statement. Two patients could not undergo knee MRI due to their clinical conditions. Initial knee MRIs were performed on six patients. After six months, only two patients underwent the second bilateral knee MRI. Both patients were neurologically classified as Frankel A. An increase in T2 values on the six-month MRI was observed for both knees, especially in the patellofemoral joint. CONCLUSION: The absence of muscle contractions seems to be deleterious to normal human knee cartilage even in the presence of a normal range of motion. Further studies with a larger number of patients, despite their high logistical complexity, must be performed to confirm this hypothesis.