Related Experiment Video
Updated: Jun 13, 2025
Reverse Total Shoulder Arthroplasty
Published on: July 5, 2011
The influence of glenosphere size and glenoid-sided offset on shoulder stability following reverse total shoulder
Nhi Nguyen1, Yichen Huang1, Franziska Eckers2
1Department of Biomedical Engineering, University of Melbourne, Parkville, VIC, Australia.
Background:
Recurrent instability continues to be a common complication following reverse total shoulder arthroplasty (rTSA); however, the influence of implant size and offset on joint compression and resistance to subluxation is poorly understood. The purpose of this study was to investigate the effect of glenosphere size, glenoid lateralization, and inferior offset on joint stability following rTSA using the Zimmer Trabecular Metal Reverse Plus shoulder system.
Methods:
rTSA was performed on 8 fresh-frozen human cadaveric scapulae with the subscapularis tendon transected at its humeral insertion. Specimens were mounted onto a custom testing rig and physiological joint loading, which was computed using specimen-specific musculoskeletal models, was applied in 45° of scapular plane abduction with (1) neutral rotation and (2) 90° internal rotation. At each joint position, glenosphere lateralization (+0, +3, and +5 mm) was varied for each glenosphere size (36 and 40 mm). Eccentric (inferior offset) glenoid positioning was also investigated in each glenosphere size. For each configuration, the shear force required to dislocate the rTSA anteriorly was quantified.
Results:
In the abducted and internally rotated shoulder, significantly more force was required to dislocate the shoulder anteriorly with the larger neutral-offset glenosphere compared to that in the smaller, neutral-offset glenosphere (mean difference: 6.2% body weight, P = .048). However, the use of a smaller, + 3 mm or +5 mm offset glenosphere resulted in equivalent anterior shoulder dislocation force to that in the larger, neutral-offset glenosphere (P > .05). In the abducted and internally rotated shoulder, lateralization of the larger glenosphere had no significant effect on shoulder dislocation force (P > .05). The inferior offset larger eccentric glenosphere produced only minor increases in stability when the arm was positioned in abduction and internal rotation (P > .05).
Conclusion:
In a position of rTSA instability (combined abduction and internal rotation), use of a larger glenosphere results in greater joint stability than that of a smaller glenosphere; however, lateralization of a smaller glenosphere increases joint stability to equivalent levels of that associated with the neutral-offset larger glenosphere. The isolated effect of increasing glenosphere eccentricity on shoulder stability following rTSA appears negligible in the position of instability.
