Humeral offset as a predictor of outcomes after reverse shoulder arthroplasty

Abstract

Introduction: The Grammont-style reverse shoulder arthroplasty (RSA) relies on medialization and distalization of the shoulder center of rotation. Lateralized designs have recently gained popularity. The amount of lateralization, however, remains a controversial topic. The purpose of this study was to correlate the change in humeral offset (HO) with outcomes and complications following RSA. We hypothesized that a lateralized HO following RSA would be associated with improved range of motion (ROM), better patient-reported outcomes (PROs), and fewer complications.

Materials and methods: A consecutive series of 104 patients (109 shoulders) was retrospectively evaluated. All patients underwent primary RSA by 2 shoulder and elbow fellowship-trained orthopedic surgeons at 2 different centers. Inclusion criteria was a primary RSA with at least 1-year follow-up. All patients had the HO measured on a preoperative and a postoperative Grashey radiograph, and the change in HO was calculated (ΔHO = _PostHO-_PreHO). A negative value was defined as a medialized HO and a positive value as a lateralized HO. ROM and primary outcomes, including forward elevation (FE), external rotation (ER), internal rotation (IR), Subjective Shoulder Value (SSV), and American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) score, were collected. Complications and revisions were also reported.

Results: The mean age was 72 years with a mean follow-up of 22.3 months. The average FE (92° vs. 148°), ER (34° vs. 44°), SSV (35% vs. 87%), and ASES score (37.2 vs. 81.2) increased significantly (all P < .01) compared with preoperative values. The HO was medialized postoperatively in 63 shoulders and lateralized in 46 shoulders. No statistically significant differences in the mean values for postoperative FE (147° vs. 146°, P = .892), ER (43° vs. 45°, P = .582), IR (L3 vs. L3, P = .852), SSV (88% vs. 85%, P = .476), and ASES score (81.3 vs. 81.1, P = .961) were found between the groups. However, there was significantly more improvement in ER in the lateralized HO cohort than the medialized cohort (16° vs. 7°, P = .033). Six shoulders, 5 medialized and 1 lateralized HO, demonstrated scapular notching and remained asymptomatic. Five shoulders, 4 medialized and 1 lateralized HO, experienced at least 1 instability incident, and 2 shoulders with medialized HO had an acromion/scapular spine fracture. Overall, 2 shoulders with medialized HO underwent revision surgery because of instability.

Conclusions: Although RSA provides significant improvement in ROM and PROs regardless of postoperative HO, restoring baseline HO or lateralization beyond baseline may be favorable for improving ER and decreasing complications following RSA.

Keywords: RSA; Reverse shoulder arthroplasty; humeral lateralization; humeral offset; lateralization; shoulder arthroplasty.