[Measurement study of anatomical shape and size in Japanese elbow joints]

Recently, total elbow replacement has been developed for reconstruction of destructed elbow joints. However, various complications occurred in the constrained or semi-constrained types of elbow replacement, while unconstrained type such as surface replacement showed lower incidence of such complications. On the other hand, development of the elbow prosthesis needs anatomical measurement of the elbow for adaptation to the need of Japanese. Basically, prosthesis should be designed based on the anatomical and biomechanical analysis. In this study, elbow from 36 Japanese cadavers were measured in the outer contour and microradiograms of the sectioned samples. Midline axes of the humerus and ulna, and the center of both medial and lateral epicondyles are fixed as standardized lines for the study in the elbow measurement. The trochlea is situated slightly anteriorly from the midline of the humerus. Width of the trochlea is 21.4 +/- 2.6 mm on the right side and 21.1 +/- 2.8 mm on the left at the anterior margin. At the distal margin, the width is 23.5 +/- 2.8 mm on the right and 23.3 +/- 2.6 mm on the left, and at the posterior margin, 23.9 +/- 3.6 mm on the right and 23.5 +/- 2.8 mm on the left. Saggittal section of the humeral end shows almost complete circle in the articular surface of the trochlea. The diameter is 19.1 mm on the right and 19.3 mm on the left at the longitudinal axis of the humerus, 17.6 mm on the right and 17.7 mm on the left at the central groove, and 24.5 mm on the right, 22.6 mm on the left at the medial margin. Anterior angulation of the trochlea is about 12 degrees. Central line of the trochlea corresponds to the center of the flexion-extension of the elbow, but angulated by 8 degrees from the humeral axis from the anterior view, and internally rotated by 3 degrees from the center of the both epicondyles from the bottom view. In the measurement of the incisura trochlea, opening distance is 18.5 +/- 2.1 mm on the right, 18.5 +/- 2.0 mm on the left, and the depth is 11.8 mm on the right, 11.6 mm on the left at the mean. Forward angulation of the incisura is 30.8 degrees on the right and 28.3 degrees on the left. Width of the olecranon is 25.0 +/- 3.2 mm on the right, 25.0 +/- 2.9 mm on the left and the thickness is 18.6 +/- 1.6 mm on the right, 18.7 +/- 1.8 mm on the left. The central line of the olecranon is supero-laterally angulated about 7 degrees from the longitudinal axis of the ulna. This angulation and lateral opening of the central line of the trochlea seems to produce carring angle of the elbow. Measurement of the elbow size and shape is discussed for designing elbow prosthesis and some biomechanical problems are also represented.