Glenoid lateralization angle influences the rate of scapular notching after reverse shoulder arthroplasty: A retrospective cohort study on 139 patients with minimum 2 years follow up from the FP-UCBM Shoulder Study Group.

Abstract

The glenoid lateralization angle (GLA), humeral lateralization angle (HLA), glenoid distalization angle (GDA), and humeral distalization angle (HDA) are new coronal parameters used to assess glenoid and humeral positioning in reverse shoulder arthroplasty (RSA). This study aimed to correlate these angles with scapular notching (SN) and clinical outcomes to guide component placement. A retrospective analysis of 139 patients undergoing primary RSA was performed. Clinical outcomes, including Constant-Murley score, simple shoulder test, visual analog scale, and range of motion, were collected preoperatively and at 24 months postoperatively. Radiographic evaluation included the measurement of GLA, HLA, GDA, and HDA on Grashey projection X-rays, alongside the incidence and grade of SN. GLA was significantly associated with a reduced probability of SN (<i>p</i> = .002), with a threshold of 51.5° identified as critical for increased notching risk. No correlation was found between clinical outcomes or ROM and any of the measured angles (<i>p</i> > .05). Radiographic reliability was high (κ = 0.89). GLA, HLA, GDA, and HDA are reproducible measures. Only reduced glenoid lateralization (GLA < 51.5°) was linked to increased scapular notching, underscoring its importance in preoperative planning, while distalization and humeral angles showed minimal clinical influence. Level III cohort study.