A morphological analysis of the humeral capitellum with an interest in prosthesis design.

INTRODUCTION Although interest in capitellar arthroplasty is increasing, the morphology of the capitellum has not been fully characterized. Our purpose was to quantify the anthropometric features of the capitellum with an interest in arthroplasty design. We hypothesized that the shape is more complex than originally believed, and cannot be accurately modeled as a spherical structure. METHODS Fifty cadaveric human elbows underwent helical computer tomography scans. After reconstruction and establishment of a coordinate system for the distal humerus, circle-fits were applied to each of the 1-mm-thick slices. Sagittal radii of curvature were calculated every 10° of flexion around each circle (0-130° of flexion). A single transverse radius was calculated at 60° of flexion. The surface of the capitellum was described by sagittal and transverse radii of curvature and the footprint by height and width. These pairs of parameters were correlated to determine their strength of association. RESULTS The average height was 23.2 ± 2.9 mm (range, 18.3-29.5), while the average width was 13.9 ± 2.3 (range, 9-19). The sagittal radius of curvature was 11.6 ± 1.4 mm (range, 8.7-14.8), and the transverse radius was 14.0 ± 3.0 mm (range, 9.6-20.9). Correlations of height and width and sagittal and transverse radii were significant (R = .547, .705) (P < .01). Sagittal and transverse radii and height and width were significantly different (P < .001 for each pair). CONCLUSION The capitellum does not have a spherical surface or a circular footprint. There is substantial variability in the relationship between the height and width, and between the surface radii, that may be difficult to replicate with an off-the-shelf implant.