Positioning of the metaglene in reverse shoulder arthroplasty: deltopectoral versus anterosuperior approach: a prospective randomized trial.

BACKGROUND:
The primary objective of this study was to determine whether there are differences in metaglene positioning related to the approach used (deltopectoral vs. anterosuperior) in primary reverse shoulder prosthesis (reverse shoulder arthroplasty) implantation. The hypothesis was that there would be no differences in metaglene positioning between the 2 approaches.

METHODS:
A prospective randomized trial was designed to evaluate metaglene positioning in primary reverse shoulder arthroplasty. The patients included were allocated to either the deltopectoral approach (group I) or the anterosuperior approach (group II). Glenosphere overhang and glenosphere tilt were assessed using the methods described by Lévigne et al, Simovitch et al, and Kempton et al, and the beta angle was assessed as described by Maurer et al. The functional outcome was assessed with the Constant score at 2 years' follow-up. Scapular notch development and complication rates were also recorded.

RESULTS:
A total of 98 patients (77 women and 21 men) were randomized and allocated to group I (49 patients) or group II (49 patients). The mean age of the patients was 74.4 years (standard deviation, 6.3 years). Glenosphere overhang did not show significant differences between groups (6.5 mm in group I vs. 6.1 mm in group II by the Lévigne method, P = .482; 2.2 mm in group I vs. 2.1 mm in group II by the Simovitch method, P = .08). Glenosphere tilt was significantly different between groups (94.6° in group I vs. 86.8° in group II by the Lévigne method, P < .001; 125.9° in group I vs. 119.4° in group II by the Kempton method, P = .002). This was also the case for the prosthesis-scapular neck angle (94.6° in group I vs. 86.8° in group II, P < .001). Moreover, the postoperative beta angle was significantly different between groups (78.6° in group I vs. 73.8° in group II, P = .001). No significant differences were noted in terms of functional outcomes as measured with the Constant score (P = .16). No significant differences between groups were noted relative to scapular notch development and the overall complication rate.

DISCUSSION:
The deltopectoral and anterosuperior approaches do not differ relative to the craniocaudal positioning of the metaglene, but a slight superior tilt can be expected when using the anterosuperior approach. Both approaches yield comparable functional outcomes, scapular notch development, and complication rates at 2 years' follow-up.