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The Effect of Lateralization on the Rotator Cuff Following Reverse Shoulder Arthroplasty

Stephanie Muh, MD

Read complete study: Clinical Outcomes after Reverse Shoulder Arthroplasty with and without subscapularis repair: The Importance of considering glenosphere lateralization

There continues to be significant debate on whether subscapularis repair is necessary during reverse total shoulder arthroplasty. Historically subscapularis repair was felt to be necessary to provide anterior soft tissue stability and help prevent post-operative dislocation. There have been multiple articles written on both the advantages and disadvantages of subscapularis repair. It should be noted that most previous articles that strongly advocated subscapularis repair included the traditional Grammont-style prosthesis with a medialized glenosphere and valgus medialized humeral stem (155 degrees).

This article retrospectively reviews patients who underwent reverse total shoulder arthroplasty (RTSA). They first stratified the subscapularis repair group versus no repair. The authors then looked at the effects of glenosphere lateralization (0mm lateralization vs +3 or +6mm) in both groups to determine if this played a significant role. The humeral stem used in the study has a neck shaft angle of 147 degrees but a humeral stem with no lateralization. ASES score from baseline was the primary outcome measured with a minimum of two-year follow-up.

The study demonstrated patients with no subscapularis repair and lateralization had the most overall improvement in ASES scores. This supports the design rationale of the Equinoxe® reverse shoulder system.

Overall, the authors found no difference in ASES scores when comparing subscapularis repair versus no repair. The authors also reported that subscapularis management and lateralized glenosphere individually did not have significant effect on ASES scores. However, analysis did find that patients with subscapularis repair with a lateralized glenosphere did worse compared to subscapularis repair with medialized glenosphere and no repair with lateralized glenosphere.

This article demonstrates the impact of the combined effect of subscapularis management with glenosphere lateralization on clinical outcomes. The study demonstrated patients with no subscapularis repair and lateralization had the most overall improvement in ASES scores. This supports the design rationale of the Equinoxe® reverse shoulder system.

The Equinoxe system is classified as a medial glenoid/lateral humeral design that lateralizes the greater tuberosity to sit in a more anatomic position while maintaining the center of rotation 2mm off the glenoid face. This design allows the construct to maintain a deltoid moment arm that is similar the original Grammont-style RTSA while lateralizing the overall construct, as demonstrated in the image below.

As this study has demonstrated, subscapularis repair influences overall improvement in a lateralized design. Patients with no subscapularis repair and lateralization had overall the most improvement in ASES scores. Therefore, it is critically important to understand the different types of reverse shoulder prostheses on the market, how much lateralization each has and where that lateralization is coming from.

Stephanie Muh, MD, is deputy chief of service in the department of orthopaedics at Henry Ford Hospital West Bloomfield where she specializes in shoulder and elbow reconstruction, rotator cuff repair and arthritis. Dr. Muh completed her residency in orthopaedic surgery at the Henry Ford Hospital and shoulder and elbow fellowship at Case Western Reserve University/University Hospitals of Cleveland.

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