Radiographic humeral head restoration after total shoulder arthroplasty: does the stem make a difference?

Background: Humeral stem designs for total shoulder arthroplasty have varied over the years, with a recent trend toward shorter stems. The purpose of this study was to examine the impact of humeral component stem length on the ability to restore the native humeral head anatomy. Methods: We performed a retrospective review including patients who underwent total shoulder arthroplasty for primary osteoarthritis between 2007 and 2017 with complete operative reports and adequate radiographs. Surgical data including stem design were collected. Preoperative and postoperative radiographic measurements of the center of rotation (COR), humeral head height (HH), and neck-shaft angle were performed. Restoration of the native humeral anatomy was deemed "acceptable'' based on postoperative differences in the COR <= 3 mm, HH <= 5 mm, and neck-shaft angle > 130 degrees. Deviations between preoperative and postoperative measurements were compared across stem types. All available 2-year stemless implant radiographs were also analyzed. Results: In total, 261 patients were included, with 31 stemless, 43 short-stem, and 187 standard-stem implants. There was no significant difference in COR restoration in the x-axis direction (P = .060) or y-axis direction (P = .579). There was no significant difference in restoration of acceptable HH by stem type (P = .339). Stemless arthroplasty implants were more likely to be placed in varus (22.6%) compared with short-stem (7.0%) and standard-stem (3.7%) designs (P < .001). Conclusion: Restoration of humeral anatomic parameters occurred significantly less with stemless implants than with short- and standard-stem implants. The stem of a shoulder arthroplasty implant aids surgeons in accurately restoring patient-specific anatomy. (C) 2020 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.