An anthropometric study of the distal humerus.

BACKGROUND: The optimal articular shape for distal humeral hemiarthroplasty has not been defined because of a paucity of data quantifying the morphology of the normal distal humerus. This study defines the osseous anatomy and anatomic variability of the distal humerus using 3-dimensional imaging techniques. METHODS: Three-dimensional surface models were created from computed tomography scans obtained from 50 unpaired human cadaveric elbows. Geometric centers of the capitellum and the trochlear groove defined the anatomic flexion-extension axis. A coordinate system was created, and the distal humerus was sectioned into 100 slices along this axis. The C line was defined as the line of best fit connecting the geometric centers of each of the slices. RESULTS: The anatomic flexion-extension axis of the distal humerus was found to be an average of 1° ± 1° from the C line (range, 0°-3°) in the coronal plane and 2° ± 1° (range, 0°-7°) in the transverse plane. The average trochlear width was 22 ± 3 mm, and the average trochlear height was 18 ± 2 mm. The mean width of the capitellum was 17 ± 2 mm; the height was 23 ± 2 mm (P < .001). CONCLUSIONS: The difference in the capitellum width and height demonstrates that the capitellum is ellipsoid, not spherical. A data bank of humeral dimensions may be used for the development of future distal humeral hemiarthroplasty implants. A more anatomic implant may optimize kinematics and maximize contact area, thus minimizing contact stresses on the native ulna and radius.

Measurements of the ispilateral capitellum can reliably predict the diameter of the radial head.

BACKGROUND: There is no validated method to determine the correct diameter of a radial head implant when the radial head is too comminuted to function as a template or during revision surgery when the radial head has been previously excised. The purpose of this study was to determine if ipsilateral capitellar dimensions could be used to predict the diameter of the radial head; and hence to assist with implant selection. METHODS: Computer tomography scans of 50 normal elbows were used to generate 3D models. Measurements of the radial head included the maximum (Dmax) and minimum (Dmin) outer diameters and the maximum (Dishmax) and minimum (Dishmin) articular dish diameters. Measurements of the humerus included the width of the capitellum (CAPwidth), and the width from the lateral aspect of the capitellum to the lateral trochlear ridge (CAP-TROCHridge). Relationships were determined with Pearson bivariate coefficients. RESULTS: The mean radial head dimensions were Dmax = 24.7 ± 2.3 mm, Dmin = 23.5 ± 2.3 mm, Dishmax = 18.2 ± 1.9 mm and Dishmin = 16.8 ± 1.7 mm. The mean capitellar measurements were CAPwidth (18.4 ± 1.4 mm) and CAP-TROCHridge (23.0 ± 2.1 mm). The most significant correlations were found between Dmax and CAP-TROCHridge (R = .90, P < .001) and Dmin and CAP-TROCHridge (R = .90, P < .001). DISCUSSION: Radiologic measurements of the capitellum are useful in the estimation of native radial head diameter. The CAP-TROCHridge measurement was very strongly correlated with both the maximum and minimum diameters of the radial head. This suggests that CAP-TROCHridge may be useful to accurately predict the native radial head diameter. These morphological relationships were plotted to produce an implant selection chart for radial head sizing applicable to any implant system. LEVEL OF EVIDENCE: Basic science, anatomy study, CT imaging.