Does excessive lateralization influence tuberosity healing in reverse total shoulder arthroplasty for proximal...

This study evaluated the influence of stem global lateralization on tuberosity consolidation and functional outcomes in patients undergoing reverse total shoulder arthroplasty (rTSA) for proximal humeral fractures (PHFs).

A retrospective, two-institution study included patients who underwent rTSA for acute PHFs implanted with one of 3 stems: the Arrow (global lateralization 21.4 mm), the Humelock II (11.2 mm), or the Unique (14.7 mm). Stems were classified as very highly lateralized (VHL; >20 mm, Arrow) or lateralized (L; 10-15 mm, Unique and Humelock II). Tuberosity consolidation was assessed radiographically at a minimum 12-month follow-up. Functional outcomes included forward flexion, external rotation, visual analog scale pain, and Constant Murley score (CS). The lateralization shoulder angle (LSA) and distalization shoulder angle were measured and compared across groups. Complication and reoperation rates were recorded.

A total of 113 patients were included: Arrow (N = 53), Humelock II (N = 40), and Unique (N = 20), comprising 53 in the VHL group and 60 in the L group. The overall consolidation rate was 82.1%. Nonunion rates differed significantly across stems (P = .018): 24.5% for the Arrow, 10.0% for the Humelock II, and 0% for the Unique, with a significant dose-response trend between increasing lateralization and increasing nonunion rate (P = .022). Patients achieving consolidation demonstrated significantly better forward flexion, external rotation, CS, and visual analog scale pain than those with nonunion (P < .05). Even among consolidated patients, the VHL group demonstrated significantly lower forward flexion, higher pain scores, and lower CS than the L group (P < .05). LSA values were similar across all consolidated groups despite a nearly 10 mm difference in global lateralization (P = .112).

A significant dose-response relationship between increasing stem lateralization and tuberosity nonunion rate was observed, with functional consequences extending beyond nonunion alone. Post-operative LSA does not reliably reflect the local mechanical environment at the tuberosity-implant interface. These findings identify proximal stem lateralization as a potentially important modifiable determinant of outcomes after fracture rTSA and underscore the need for prospective studies to define the threshold of lateralization compatible with reliable tuberosity healing.