Eight years ago, a patient had this type of reverse total shoulder implanted in the right shoulder. Note the close proximity between the humeral polyethylene and the inferior screw (arrow).
Seven years later the patient was complaining of shoulder pain and had the x-ray shown below. The arrow points to scapular notching from contact of the bone of the scapular with the polyethylene of the humeral cup. This notching has exposed the inferior screw.
Eight months later, the shoulder dislocated and could not be stably reduced. The x-ray below shows the dislocated reverse with the notched scapula.
At revision surgery, the polyethylene was seen to be eroded so that it no longer functioned as a complete cup - this allowed the shoulder to dislocate. The appearance of the polyethylene is show below.
We revised this shoulder by removing the prominent screw, replacing the glenosphere with one of a larger diameter of curvature, and using humeral spacers to improve stability by increasing the compressive force at the joint.
This case demonstrates that notching can be a problem and that the resulting loss of the polyethylene concavity can allow the reverse total shoulder to dislocate.
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