Patient height may not determine optimal glenosphere size for reverse shoulder arthroplasty
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Selection of glenosphere size based on patient height did not improve range of motion or patient-reported outcome measures after reverse shoulder arthroplasty, according to published results.
Researchers separated 589 primary reverse shoulder arthroplasties (Equinoxe, Exactech) into groups based on whether patients had a glenosphere size of 38-mm or 42-mm and calculated predictive accuracy in relation to height and sex for predicting glenosphere size. Researchers compared improvements in active range of motion and patient-reported outcome measures, including American Shoulder and Elbow Surgeons score, Constant score, simple shoulder test score and University of California, Los Angeles score, based on glenosphere size as a function of height.
Patient height and sex had a strong association with surgeon selection of glenosphere size, according to results of a logistic regression analysis. Researchers found surgeons preferentially treated patients with shorter heights with 38-mm glenospheres and patients with taller heights with 42-mm glenospheres. However, results showed glenosphere size and patient height had no statistically significant interaction effect on improvements in range of motion or patient-reported outcome measures.
“Surgeons should consider other variables when selecting a particular glenosphere size, as similar clinical improvements can be expected between 38- and 42-mm implants using a lateralized humeral [reverse shoulder arthroplasty] RSA design,” the authors wrote. – by Casey Tingle
Disclosures: Schoch reports he is a paid consultant and receives royalties from Exactech. Please see the study for all other authors’ relevant financial disclosures.
Perspective
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Michael Q. Freehill, MD, FAAOS
Evidence correlating glenosphere size and functional outcomes has led to variable conclusions. In this multicenter, retrospective study, Bradley S. Schoch, MD, and colleagues assert that surgeons tend to stay in their lane when determining glenosphere size, revealing height often parallels implant sizing. The results of the study, however, did not yield a difference in outcome in terms of range of motion when evaluating glenosphere size. Ultimately, the study validates that glenosphere size may be less important than baseplate position, inclination and soft tissue tension, in determining outcomes. Furthermore, biomechanical studies have suggested that larger glenospheres may yield greater volumetric wear poly, which, in theory, could generate progressive osteolysis.
The results of this study would support that glenosphere dimensions should be used to avoid scapular impingement, enhance stability and provide balanced soft tissue tension, all of which can be evaluated intraoperatively. The ongoing evolution of preoperative planning software will likely provide greater insight in the near future as surgeons will be able to prospectively follow patients, thereby determining with greater reliability which implant variables and anatomical variances exert greater influence on functional outcomes.
Alina Health System
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