Automatic Determination Of A Morphology-based Anatomical Coordinate System Of The Human Patella

To determine an anatomical coordinate system (ACS) using the morphology of the patella. 3D patella surface models (PSM) were isolated from CT images (512x512, 0.625 slice thickness) of 10 subjects' knees (5 M, 25+ or -4.2 yrs; 5 F, 26+ or -2.3 yrs). The center of mass of the PSM defined the origin of the ACS. The 3rd principal axis of inertia served as the anterior/posterior (AP) axis. The proximal/distal (PD) axis was aligned with the posterior vertical ridge by rotating the 1st and 2nd inertial axes about the AP axis until the variation in the medial/lateral (ML) location of the ridge was minimized. The mean angle and 95% CI between the resultant AP, ML, and PD axis and each subject's axis was 1.3[degrees] (CI: 0.9[degrees] -1.7[degrees]), 3.0[degrees] (CI: 1.8[degrees] - 4.2[degrees]), and 3.2[degrees] (CI: 2.1[degrees] - 4.3[degrees]) respectively. The mean distance between the CO and individual origins was 0.7 mm (CI: 0.5 mm - 0.9 mm).