ANTHROPOMETRIC STUDY OF NORMAL GLENOHUMERAL RELATIONSHIPS

Ninety-three cadaveric proximal humeri and matching scapulae with no e vidence of shoulder disease were obtained. High-resolution roentgenogr ams were made. They were then digitized, and a custom computer program was used to obtain periosteal and endosteal dimensions (humeral canal width, shaft width, tuberosity offset, head offset, radius of curvatu re, head diameter, canal flare index, glenoid height and depth, are of enclosure, radius of curvature, and depth of cancellous bone, among o thers). Statistical analyses included correlations among pairs of dime nsions, regression analysis, and confidence intervals to estimate each geometric parameter. To represent the degree of conformity and constr aint between the humeral head and glenoid, a conformity index (radius of head/radius glenoid) and constraint index (arc of enclosure/360) we re calculated for each shoulder. Most of the parameters measured appro ximated a Gaussian distribution. Pairwise correlations of the geometri c parameters showed that many were significantly associated at the 5% level (p < 0.05) with a high correlation coefficient (r > 0.4), meanin g that the variations between the parameters were not purely random bu t rather they were related and that this relationship was useful in a predictive sense. With these key parameters identified, one can design components with an optimum fit or match an existing design to a patie nt's anatomy with a high degree of accuracy. No correlation was found between the radii of curvature for the humeral head and glenoid in eit her the coronal or sagittal plane or between the humeral head diameter and arc of enclosure. The mean conformity index was 0.72 in the coron al and 0.63 in the sagittal plane. Only 16% of the specimens had a con formity index greater than 0.9, indicating the radii of curvature matc hed. The vast majority had a more curved humeral head and flatter glen oid. Also, there was more constraint to the glenoid in the coronal ver sus sagittal plane (constraint index = 0.18 vs 0.13). These anatomic f eatures help prevent superior-inferior translation of the humeral head but allow translation in the sagittal plane. This database of basic a natomic geometry defines the anatomic relationships of the proximal hu merus and glenoid cavity that allow for a precise bone-implant fit and assesses the match between the shape of existing components and the p atient's anatomy.