Morphology of the scapula relative to the reverse shoulder prosthesis

To analyse the morphology of the scapula relative to the reverse shoulder prosthesis.

Scapulas of 46 women and 27 men aged 16 to 84 (mean, 53) years with proximal humeral fractures (n=52) or recurrent antero-inferior instability (n=21) were assessed using 3-dimensional computed tomography (CT). For comparison, 108 cadaveric scapulas with unknown epidemiology were assessed using a goniometer and a caliper. The length of the glenoid neck, the angle between the glenoid surface and the upper posterior column of the scapula, and the angles between the major craneocaudal glenoid axis and (1) the base of the coracoid process and (2) the upper posterior column of the scapula were assessed.

The length of the glenoid neck was classified into short and long. In the respective CT and cadaveric groups, the anterior glenoid neck was short in 42% and 18% of scapulas and long in 58% and 82%, whereas the posterior glenoid neck was short in 34% and 60% of scapulas and long in 66% and 40%. The angle between the glenoid surface and the upper posterior column of the scapula was classified into types I (50-52 degrees) and II (62-64 degrees). In the respective CT and cadaveric groups, 61% and 71% of scapulas were type I and 39% and 29% were type II. All differences between groups were significant. The mean angles between the major craneocaudal glenoid axis and (1) the base of the coracoid process and (2) the upper posterior column of the scapula were 18 and 8 degrees, respectively.

Because of variations in scapular morphology, individualised adjustment is needed for reverse shoulder prostheses. Three-dimensional CT is valuable in preoperative planning.