The Y plane is a reliable CT-based reference for glenoid component positioning in shoulder arthroplasty

Purpose: To determine the reliability of anatomic references for mediolateral component positioning in shoulder arthroplasty.

Materials and methods: The computed tomography scans of 86 shoulders free of arthritic or anatomic deformities were studied. Two surgeons independently digitized a series of points, including the intersection of the 3 bone branches of the scapular spine (Y), the center of the glenoid surface (G), the most medial point of the scapula (MS), the cortical convergence (CC) of the anterior and posterior margins of the glenoid, the base of the coracoid (BC), the anterior (HA) and posterior (HP) margins of the subchondral bone.

Results: The mean mediolateral distances between G and Y, BC, CC were respectively - 19.6 mm, - 1.5 mm, and - 36.8 mm. The consistency of anatomic landmarks was greatest for Y (standard deviation (SD) =2.3 mm; interquartile range (IQR) =3 mm), compared to BC (SD = 4.6 mm; IQR = 7 mm), and CC (SD = 6.6 mm; IQR = 8 mm). The repeatability of anatomic landmarks was excellent for all measurements. The mean ratios (relative to humeral head size) of distances between G and Y, BC, CC were respectively - 0.45, - 0.04, and - 0.85. The consistency of ratios was greatest for Y (SD = 0.05; IQR = 0.06), compared to BC (SD = 0.11; IQR = 0.14), and CC (SD = 0.13; IQR = 0.17). The repeatability of ratios was excellent for Y and BC, while it was good for CC.

Conclusions: The Y-plane is a reliable reference for glenoid component positioning in shoulder arthroplasty, with a consistent distance from the center of the glenoid surface, and could therefore be suitable for preoperative planning.

Study design: Level III, comparative anatomic study.