Optimizing glenosphere position and fixation in reverse shoulder arthroplasty, Part One: The twelve-mm rule

Effects of the humeral tray component positioning for onlay reverse shoulder arthroplasty design: a biomechanical analysis

“…5,19,36 This retroversion level was chosen because it appears to be the best compromise in many reported studies for avoiding inferior impingement and allowing a good balance of external and internal rotation (at 20 of humeral abduction). 24,25 However, humeral retroversion can also affect inferior and superior impingement and could have affected the results of this study. Further investigation is needed to understand the effect of humeral retroversion in humeral tray positioning.…”

“…Nyffeler et al 28,29 and Simovitch et al 33 first recommended the importance of placing the glenoid component with an inferior offset and inferior tilt. Kelly 24 reported that by using the ''12-mmrule'' for glenoid pin positioning, adequate inferior glenoid fixation can be achieved independently of the scapular's pillar anatomy. Frankle et al, 16 Kalouche et al, 22 and Valenti et al 39 all advocated the concept of lateralizing the center of rotation with the prosthetic glenoid, whereas Boileau et al 7,8 described bony lateralization with the BIO-RSA (Tornier, Warsaw, IN, USA) bony-increased-offset surgical procedure.…”

The use of an eccentric glenosphere compared with a concentric glenosphere in reverse total shoulder arthroplasty: two-year minimum follow-up results

“…Attempts have been made to decrease the risk of notching by placing the metaglene more distally on the glenoid cavity, thus allowing the glenosphere to extend below the inferior border of the glenoid. The effect of the distalisation of the glenosphere is to significantly improve the abduction and adduction motion, which would decrease contact between the humeral polyethylene cup and the scapular neck [7,9,17]. However, a recent study has shown that this technique alone is not sufficient to avoid notching [13].…”

“…Simovitch et al [8] confirmed that the craniocaudal positioning of the glenosphere, and the angular relationship between the glenosphere and the scapular neck, are highly correlated with the quality of the clinical outcome and the incidence or severity of scapular notching. To avoid this drawback, a new glenosphere was introduced in the Systema Multiplana Randelli (SMR) reverse shoulder prosthesis which has an eccentric shape (eccentric glenosphere), making it possible to lower the centre of rotation and theoretically decrease or avoid scapular notching compared with the current concentric glenosphere [7,9].…”

Optimal screw placement for base plate fixation in reverse total shoulder arthroplasty

“…This study performed computer tomography (CT) scans on dried human scapulae and templated that on average, the base plate would be flush by drilling the posthole 12 mm superior to the inferior glenoid rim and would thus minimize scapular notching. 15 Once obtaining optimal base plate positioning, the focus turns to placing the supporting screws into regions with the best bone stock. Several studies have shown a direct relationship between increased screw pullout strength with increased cortical thickness.…”