Articular surface failure in hybrid anatomic glenoid components: a unique failure mechanism.

PURPOSE: Glenoid loosening is a common failure mechanism of anatomic total shoulder arthroplasty (TSA). New hybrid fixation glenoids allow bony ingrowth and decrease the rates of glenoid loosening. The purpose of this study is to describe a new failure mode of polyethylene dissociation from the ingrowth cage in a single implant design.

METHODS

A retrospective review was performed using an institutional shoulder arthroplasty database of a single hybrid cage glenoid (Exactech, Gainesville, FL). Implants demonstrating this failure mechanism were investigated.

RESULTS

Five out of 206 (2.4%) primary TSAs with cage glenoids performed at our institution and 2 referred for revision suffered glenoid articular face failure. Mean age was 57 (range 38-67 years). Two of 7 failures (29%) occurred secondary to trauma. Failure occurred at mean 14 months after index arthroplasty (range 0-30 months). Revision occurred at mean 24 months after index arthroplasty (range 6-39 months). Six of the 7 patients (86%) had posteriorly augmented glenoids. All 6 patients who had available pre-failure radiographs demonstrated off-axis deviation between the peripheral pegs and central cage (mean 4.8°, range 3°-6°), which may predispose the implant to failure by pre-stressing the material interface.

CONCLUSION

Failure between the glenoid articular face and the central ingrowth cage is a unique failure mechanism to modular hybrid ingrowth glenoids. We hypothesize that this is predisposed by off-axis drilling leading to pre-stressing of the material interface. Surgeons should be aware of the existence of this failure mechanism, particularly when seeing patients with acute pain after an otherwise unproblematic TSA.