The influence of glenoid component position on scapular notching: a detailed radiographic analysis at midterm follow-up.

BACKGROUND

Glenoid baseplate and glenosphere positioning may affect scapular notching rates. The purpose of this study was to assess various radiographic parameters and correlate them with scapular notching after primary reverse total shoulder arthroplasty (RTSA) at a minimum follow-up time of 5 years.

METHODS

The study sample included 147 primary RTSA with good-quality postoperative radiographs at least 5 years after implantation (mean follow-up 6.1 years, range 5-12 years). The center of rotation (COR) of the glenosphere in reference to the bone-baseplate interface was medialized in 71 and lateralized in 76 shoulders, with a varus polyethylene opening angle in 134 shoulders. Preoperative and immediate postoperative radiographs were measured to determine (1) glenoid baseplate inclination: α, β, and the reverse shoulder arthroplasty (RSA) angles; (2) glenoid component inferiorization-peg glenoid rim distance (PGRD); and (3) sphere bone overhang distance (SBOD). Scapular notching was graded according to the Sirveaux classification.

RESULTS

Scapular notching was noted in 98 shoulders (67%) and classified as grade 1 in 46, grade 2 in 25, grade 3 in 20, and grade 4 in 7. There were statistically significant associations between notching and both medialized glenospheres (91% vs. 45%,  = .001) and varus polyethylene angle ( = .0001). The mean postoperative RSA angle, PGRD, and SBOD were 6.6 degrees, 23.8 mm, and +2.6 mm, respectively. Preoperative α and postoperative β, RSA, PGRD, and SBOD were all associated with notching ( < .05). The rate of reoperation was 2.7% at a minimum of 5 years, with reasons for reoperation related to component failure in only one shoulder.

CONCLUSION

Scapular notching correlates with glenoid and baseplate inclination, baseplate inferiorization, inferior glenosphere overhang, glenosphere COR, humeral polyethylene angle, and longer clinical follow-up. SBOD is a clinically useful measurement with decreased values associated with notching. It is the superior measurement in implants with eccentric glenospheres. Moderate or severe notching was seen in only approximately 15% of the shoulders. Revision surgery was extremely low in this cohort, and it was not related to notching or instability.