Summary

In primary RSA using a lateralized implant, medialization of glenoid bone-baseplate interface after eccentric reaming does not influence shoulder range of motion, patient-reported outcome scores, postoperative pain scores, baseplate loosening, or glenoid notching.

Abstract

Background

One of the major concerns with reverse shoulder arthroplasty (RSA) is dealing with the glenoid bone loss that is severe enough to compromise baseplate stability. The influence of increasing the medialization of the bone-baseplate interface (MBBI) resulting from reaming the glenoid while using a lateralized glenosphere RSA system has not been studied before. This study aims were to determine 1) What is the influence of different magnitudes of MBBI on clinical outcomes including range of motion (ROM) and patient reported outcomes (PROs)? and 2) What is the influence of increasing MBBI on the incidence of baseplate failure and scapula notching?

Methods

We retrospectively reviewed 91 patients who underwent primary RSA after a minimum 2-year follow-up. The amount of MBBI was estimated using a 3-dimensional CT scan-based computer planning software. Patients were categorized into three groups depending on whether MBBI was less than 3 mm (Group low MBBI, N = 32), between 3 mm to 5 mm (Group moderate MBBI, N = 30), or more than 5 mm (Group high MBBI, N = 29). Range of motion (ROM), American Shoulder and Elbow Surgeons (ASES) score, Simple Shoulder Test (SST) score, and scapular notching were compared between groups.

Results

Mean MBBI was 1.5 mm (range, 0.5 - 2.5 mm) in low MBBI group, 3.5 mm (range, 3.0 - 5.0 mm) in moderate MBBI group, and 7 mm (range, 5.5 – 1.0 mm) in high MBBI group. At the last follow-up, there was no statistical difference (all P > 0.05) in clinical results when compared between low, medium, and high MBBI groups for mean ASES (74 vs 67 vs 75), SST (8 vs 7 vs 9), VAS for pain (1.3 vs 2.3 vs 2,7), abduction (121° vs 120° vs 123°), external rotation at 90° abduction (60° vs 60° vs 55°), and internal rotation at back (lumbosacral vs lumbosacral vs waist). There was no correlation between the amount of MBBI and improvement in ROM in any plane. There was no baseplate loosening in any patient. There was no statistical difference (P > 0.05) in scapula notching at the final follow up in low (17%), moderate (33%), and high (24%) MBBI groups. There was no significant correlation between the amount of MBPI and postoperative change in abduction (rs = -0.12, p = 0.362), external rotation (rs = -0.11, p = 0.387, ASES score (rs = -0.1, p = 0.133), SST score (rs = 0.1, p = 0.105), and VAS for pain (rs = 0.2, p = 0.08).

Conclusions

This study found that, in primary RSA using a lateralized implant, medialization of glenoid bone-baseplate interface after eccentric reaming does not influence shoulder range of motion, patient-reported outcome scores, postoperative pain scores, baseplate loosening, or glenoid notching. Further studies with more accurate measuring techniques of MBBI and its results upon patient, implant, and surgical variables are warranted.