Reverse Glenoid Component Fixation: is a Posterior Screw Necessary?

Background: Reverse shoulder arthroplasty has become more prevalent for the treatment of complex shoulder issues. Prosthetic designs vary in both the number and orientation of screws recommended for securing the glenoid base plate. This study examined the contribution of the posterior glenoid screw for stabilizing the glenosphere by comparing constructs with no posterior screw, a standard posterior screw directed into the glenoid neck, and a long posterior screw (LPS) into the scapular spine.

Material And Methods: The Tornier RTSA glenoid implant was fixed into 2 groups of matched cadaveric scapulae. In both groups, the controls were fixed with a standard posterior screw (SPS). Matching scapulae had a screw configuration that omitted the posterior screw (NPS) in group I or utilized an LPS in group II. Specimens were tested using a "rocking-horse" protocol. During cyclic loading (50,000 cycles), the vertical displacement of the glenoid component was monitored using a digital caliper.

Results: In group I, NPS constructs demonstrated a significantly higher mean rate of loosening than SPS constructs. In group II, the LPS constructs demonstrated lower loosening rates than SPS constructs. Mean initial displacements were greater for NPS than SPS in group I and similar for SPS and LPS in group II DISCUSSION: The posterior glenoid screw contributes significantly to stability of the reverse glenoid base plate. If an SPS does not obtain good purchase into the scapula, glenoid component fixation will be enhanced by the addition of an LPS into the scapular spine.