Determining the ideal osteotomy for stemless total shoulder replacement: a cadaveric study.

Abstract

We sought to determine the angle of osteotomy that produces a circular humeral cut surface. A total of 49 cadaveric shoulders, from 25 cadavers, underwent sequential humeral head osteotomy from 180° (vertical, in line with the humeral diaphyseal shaft), in 10° increments, until the rotator cuff insertion was encountered. At each stage, the anteroposterior (AP) and superoinferior (SI) distances were recorded. The data were analyzed for normality and then assessed to determine the optimum cut angle. The AP/SI ratio is an indication of roundness. Plotting values of 1 - AP/SI (ie, error) vs. cut angle allowed us to plot the likelihood of producing a circular cut surface using a third-order curve that created the best fit to the data set (R2 = 0.99). The results from this study suggest that the optimum osteotomy angle that produces a circular cut surface is 23° from the vertical. The cohort data illustrated that at this angle, the average roundness error was 1% with a 95% confidence limit of <1%. There was no significant difference (P > .05) between sexes. The humeral head shape changes from oval to circular and then to an oval cut surface as the osteotomy angle increases from the vertical toward the horizontal. The range of angles within which the cut surface is circular, within a 10% error margin, is 18°-27° from the vertical, which is much less than the traditional osteotomy angle of 45°.