Do less medialized reverse shoulder prostheses increase motion and reduce notching?

Abstract

Background: Cuff tear arthropathy is the primary indication for total reverse shoulder arthroplasty. In patients with pseudoparalytic shoulders secondary to irreparable rotator cuff tear, reverse shoulder arthroplasty allows restoration of active anterior elevation and painless shoulder. High rates of glenoid notching have also been reported. We designed a new reverse shoulder arthroplasty with a center of rotation more lateral than the Delta prosthesis to address this problem.

Questions/purposes: Does reduced medialization of reverse shoulder arthroplasty improve shoulder motion, decrease glenoid notching, or increase the risk of glenoid loosening?

Patients and methods: We retrospectively reviewed 76 patients with 76 less medialized reverse shoulder prostheses implanted for pseudoparalytic shoulder with rotator cuff deficiency between October 2003 and May 2006. Shoulder motion, Constant-Murley score, and plain radiographs were analyzed. Minimum followup was 24 months (mean, 44 months; range, 24-60 months).

Results: The absolute Constant-Murley score increased from 24 to 59, representing an increase of 35 points. The range of active anterior elevation increased by 61°, and the improvement in pain was 10 points. The gain in external rotation with elbow at the side was 15°, while external rotation with 90° abduction increased by 30°. Followup showed no glenoid notching and no glenoid loosening with these less medialized reverse prostheses.

Conclusions: Less medialization of reverse shoulder arthroplasty improves external and medial rotation, thus facilitating the activities of daily living of older patients. The absence of glenoid notching and glenoid loosening hopefully reflects longer prosthesis survival, but longer followup is necessary to confirm these preliminary observations.

Level of evidence: Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Fig. 1

The glenosphere of the Arrow^® prosthesis is a half-sphere placed on the metal back. The center of rotation is lateralized by 8.5 mm (arrows) due to the thickness and the curve design of the metal back.

Fig. 2A–B

Photographs illustrate the design of the humeral stem. (A) The Delta III humeral stem is less lateralized. (B) The metaphysis of the Arrow^® reverse prosthesis stem is angled at 135° and is lateralized (+4 mm).

Fig. 3A–B

AP views compare (A) the Delta III prosthesis with (B) the Arrow^® prosthesis. Lateralization of both the center of rotation (point) and proximal metaphysis increases the lateral offset (arrow).

Fig. 4

A diagram illustrates the classification of Valenti et al. [27]: (1) Grade 1, small notch, confined to the scapular pillar; (2) Grade 2, notch with condensation (stable), notch outline contacts lower; (3) Grade 3, notch over the lower screw (evolving notch); and (4) Grade 4, notch extending to baseplate.

Fig. 5

Lateral offset (LO) (distance from the center of rotation to the great tuberosity) and acromion humeral distance (AH) were measured.

Fig. 6A–B

(A) A preoperative AP view shows the shoulder of a 74-old-woman with an irreparable rotator cuff tear with an eccentric arthritis (Hamada III). (B) A postoperative AP view shows the shoulder after implantation of the Arrow^® prosthesis (second generation).

Fig. 7A–B

Photographs illustrate the second-generation Arrow^® prosthesis: (A) The metal back is designed with a quadrangular central quill and an anterior plate. The component is set with two glenoid screws (15° divergent) and an accessory AP screw against shear forces. The glenosphere is impacted and screwed on the metal back. (B) The humeral polyethylene is notched at the medial side. The component is impacted and screwed on the stem.