Quantitative Analysis of Local Changes in Patellar Cartilage in Spinal Cord Injured Subjects

Most studies investigating articular cartilage changes use global parameters and neglect the large topological variation in the response of cartilage to immobilization and remobilization. We hypothesized a registration-based semi-automatic segmentation method would be highly reproducible to detect local changes in patellar articular cartilage thickness. We also hypothesized thinning of the cartilage is detectable in the smaller subregions of the patella in patients with a spinal cord injury (SCI) and the use of difference maps would allow us to detect early local thinning of the patellar cartilage. To determine the reproducibility, magnetic resonance images of the knee of seven healthy volunteers were acquired four times. Longitudinal changes were measured in the knees of seven patients with SCI as soon as possible, 6 months, and 12 months after the injury. Thickness maps and morphologic parameters for the cartilage of the patella and the four sub-regions were computed. The individual difference maps of 43% of the patients showed local areas of substantial thinning 6 and 12 months after injury.