Wednesday, February 1, 2017

Reverse total shoulder - safe baseplate fixation

Scapula fracture incidence in reverse total shoulder arthroplasty using screws above or below metaglene central cage: clinical and biomechanical outcomes

Scapular spine fractures are serious complications of reverse total shoulder arthroplasty.

These authors reviewed 318 reverse total shoulder arthroplasties (RTSAs) to identify scapular spine fractures.
Of 206 patients in the superior screw group, 9 (4.4%) experienced scapula spine fractures.
Of 112 patients in the inferior screw group, 0 had scapular spine fractures.

They also implanted RTSAs in 17 cadaveric scapula specimens with 2 screw configurations: inferior screws alone (group 1INF) vs. inferior screws with one additional superior screw (group 2SUP). 

Biomechanically, superior screw constructs (group 2SUP) demonstrated significantly (P < .05) lower load to failure (1077 N vs. 1970 N) compared with constructs with no superior screws (group 1INF). 

They concluded that the risk of scapular fractures was significantly (P < .05) for patients with no screws placed above the central cage compared with patients with superior metaglene screws.

The superior screw may not add substantially to the quality of the fixation. In an article entitled, Factors affecting fixation of the glenoid component of a reverse total shoulder prothesis, the relatively greater importance of the inferior screw in contrast to the relatively lower importance of the superior screw was emphasized.

In this type of design,  superiorly directed loads applied to the glenosphere by the humeral component are resisted primarily by the inferior screw.

Our approach to reverse total shoulder arthroplasty is to use a fixation system that uses a large central compression screw, avoiding the risks of a superiorly directed screw.