Optimizing glenosphere position and fixation in reverse shoulder arthroplasty, Part Two: The three-column concept.

Abstract

Scapular geometry is complex, and a screw-placement technique for optimizing glenoid component fixation with an Aequalis Reversed Shoulder Prosthesis (Tornier, Inc., Edina, MN) has not yet been described. Ten cadaveric human scapulae were implanted with 2 types of reverse arthroplasty baseplates, 1 with fixed-angle locking screw holes and 1 with multidirectional locking screw holes. Optimal screw placement was defined as that which maximized screw length, accomplished far cortical fixation, and attained screw purchase in good bone stock. An anterior cruciate ligament drill guide was used to find the ideal trajectory for each screw. Trajectory angles of the screws relative to the face of the baseplate are presented for what we believe is best possible fixation. Awareness of the 3 major columns of scapular bone (the base of coracoid, the spine, and the pillar) and utilization of a baseplate with variable-angle locking screws will allow optimal initial fixation of the glenosphere.