Reverse total shoulder arthroplasty with polyethylene liner dissociation/dislocation
Presentation
Left reverse total shoulder arthroplasty performed 3 years ago for rotator cuff arthropathy, now presenting with left shoulder instability and pain. Recent traumatic left shoulder dislocation which was reduced.
Patient Data
Radiographs of the left shoulder show a reverse total shoulder arthroplasty. The components are not cemented. There is subluxation of the glenohumeral metal components, but not complete dislocation. There is no acute fracture, periprosthetic lucency, or soft tissue gas. There is no significant heterotopic ossification. Inferior scapular notching is noted with corticated margins.
CT confirms left reverse total shoulder arthroplasty with subluxation. The polyethylene liner is dislocated superiorly, along the superior aspect of the glenohumeral joint. Window/levels must be adjusted to increase conspicuity of the liner and limit hardware artifact.
There is a small os acromiale / chronic acromial tip fracture.
There is severe atrophy of the rotator cuff muscles.
The entire humerus was imaged in order to measure the version of the humeral component with respect to the elbow. There was abnormal retroversion of the humeral head measuring 71 degrees with respect to the transepicondylar axis.
Case Discussion
This case shows reverse total shoulder arthroplasty with polyethylene liner dissociation from the humeral tray.
The “overlap sign”, consisting of increased overlap/contact of the glenosphere and humeral tray due to lack of intervening liner, has been described as pathognomonic of liner dissociation. Another predictive sign is when there is glenohumeral subluxation without complete dislocation. The glenohumeral joint is a finite space, so when the polyethylene liner is out of place, it prevents a complete dislocation of the glenohumeral articulation; subluxation is seen instead. CT should be performed to confirm the diagnosis. Early diagnosis is important to minimize complications, particularly ensuing metallosis in the absence of an articulating liner.
This patient had a prior shoulder dislocation, and the liner dislocation may have occurred during the prior shoulder dislocation or reduction attempt. The shoulder arthroplasty was subsequently revised. In particular, the displaced polyethylene liner was removed, and new larger glenosphere, retentive polyethylene liner, and metal humeral tray were inserted.