Patient-Specific Instrumentation Versus a Free-Hand Technique for Glenoid Baseplate and Peripheral Screw Placement in Reverse Total Shoulder Arthroplasty Using the Exactech Implant System: A Multicenter Randomized Controlled Trial.

Abstract

Accurate positioning of the glenoid baseplate and peripheral screws is critical in reverse total shoulder arthroplasty (rTSA). Patient-specific instrumentation (PSI) has been introduced to improve surgical accuracy, but its benefits over conventional free-hand techniques remain uncertain. This study aimed to evaluate the accuracy of glenoid baseplate and peripheral screw placement between PSI-assisted and conventional free-hand rTSA. We conducted a prospective, multicenter, parallel-group, single-blinded, superiority randomized controlled trial across seven tertiary centers between March 2022 and December 2024. Patients aged ≥65 years undergoing primary rTSA were randomized 1:1 to PSI or free-hand group through a centralized web-based electronic case report form. No cross-over occurred, and all analyses were performed on an intention-to-treat basis. A standardized implant system (Exactech, Gainesville, FL, USA) was used in all cases. The primary outcome was the proportion of patients with postoperative CT-based deviation error from preoperative planning, including version (≥5°), inclination (≥5°), or position offset (≥2.5 mm) errors. The secondary outcomes included continuous deviation values and accuracy of peripheral screw placement (anteroposterior gap, superoinferior gap, and length gap deviations). Effect sizes with 95% confidence intervals (CI) were reported. Of 106 patients, 53 were included in the PSI and free-hand groups each. Baseline demographics and clinical characteristics were comparable between the groups. Baseplate positioning was similar between the groups, with version error 5 ± 5° vs. 5 ± 5°, inclination error 6 ± 5° vs. 5 ± 4° (mean difference +0.9°, 95% CI -0.8 to +2.6; p=0.309), and positional offset 3 ± 2 mm vs. 4 ± 2 mm (mean difference -0.3 mm, 95% CI -1.1 to +0.5; p=0.496). Conversely, PSI significantly improved peripheral screw placement accuracy, including anteroposterior gap (-1 ± 3° vs. 1 ± 6°; mean difference -1.9°, 95% CI -3.7 to -0.1; p=0.041), superoinferior gap (-2 ± 4° vs. 1 ± 6°; mean difference -2.7°, 95% CI -4.7 to -0.8; p=0.008), superior length gap (1 ± 6 mm vs. -2 ± 8 mm; mean difference +3.0 mm, 95% CI 0.2 to 5.8; p=0.039), and inferior anteroposterior gap (1 ± 6° vs. -3 ± 6°; mean difference +4.2°, 95% CI 2.0 to 6.4; p<0.001). Additionally, clinically relevant errors (>5°) were significantly less frequent in the PSI group for anterior (11.3% vs. 43.4%; p<0.001) and superior (20.8% vs. 41.5%; p=0.035) superoinferior gap. In primary rTSA, PSI did not improve glenoid baseplate positioning compared to the free-hand technique but significantly enhanced the accuracy of peripheral screw placement. Level II; Randomized Controlled Trial; Treatment Study.