Stemless components lead to improved radiographic restoration of humeral head anatomy compared with short-stemmed components in total shoulder arthroplasty.

Abstract

Restoring the native center of rotation (COR) in total shoulder arthroplasty (TSA) has been shown to improve postsurgical function, subjective outcomes, and implant longevity. The primary purpose of this study was to compare postoperative radiographic restoration of the humeral COR between short-stem and stemless humeral implants by evaluating the mean COR shift between the 2 techniques. Secondary outcomes evaluated were comparisons of COR shift outliers, humeral head implant thickness and diameter, direction of COR shift, and neck-shaft angle (NSA). This study was a multicenter retrospective comparative study using a consecutive series of primary anatomic TSA patients who received either a short-stem or stemless humeral implant. Radiographically, COR and NSA were measured by 2 fellowship-trained surgeons using the best-fit circle technique on immediate postoperative Grashey radiographs. A total of 229 patients formed the final cohort for analysis that included 89 short stems and 140 stemless components. The mean COR shift for short stems was 2.7 mm (±1.4 mm) compared with 2.1 mm (±0.9 mm) for stemless implants (P<.001). The percentage of short-stem implant patients with a >2 mm COR difference from native was 66.0% (n=62) compared with 47.4% (n=64) for stemless (P=.006). The percentage of short-stem patients with a >4 mm COR difference from native was 17.0% (n=16) compared with 3.0% (n=4) for stemless (P<.001). The mean humeral implant head thickness for short stems was 18.7±2.2 mm compared with 17.2±1.3 mm for stemless implants (P<.001). The mean humeral head diameter for short stems was 48.7±4.4 mm compared with 45.5±3.5 mm for stemless implants (P<.001). The NSA for the short-stem cohort was 136.7° (±3.6°) compared with 133.5° (±6.0°) for stemless (P<.001). Stemless prostheses placed during TSA achieved improved restoration of humeral head COR and were less likely to have significant COR outliers compared with short-stem implants.