Aims. Scapular notching is a frequently observed radiographic phenomenon
in reverse shoulder arthroplasty (RSA), signifying impingement of
components. The purposes of this study were to evaluate the effect
of glenoid component size and glenosphere type on impingement-free
range of movement (ROM) for extension and internal and external
rotation in a virtual RSA model, and to determine the optimal configuration
to reduce the incidence of friction-type scapular notching. Materials and Methods. Preoperative CT scans obtained in 21 patients (three male, 18
female) with primary osteoarthritis were analyzed using modelling
software. Two concurrent factors were tested for impingement-free
ROM and translation of the centre of rotation: glenosphere diameter
(36 mm vs 39 mm) and type (centred, 2 mm inferior
eccentric offset, 10° inferior tilt). Results. Glenosphere size was most predictive of increased extension and
external rotation, whereas lateralization of the centre of rotation
was the most predictive factor for internal rotation. A larger diameter
of glenosphere combined with a 10° tilted configuration demonstrated
superior values for extension and external rotation, whereas the eccentric
component improved internal rotation by a mean 8.9° (standard deviation
2.7°) compared with a standard concentric glenosphere. Conclusion. Glenosphere configuration can be modified to increase range of
movement in RSA. Friction-type scapular notching was most effectively
reduced by use of a large-diameter glenosphere with 10° inferior
tilt. Cite this article: Bone Joint J 2018;100-B:1182–6