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Instability hastens polyethylene wear, however long-term usage will eventually cause wear as well. The debris generated by the wear of polyethylene in the shoulders is associated with progressive periprosthetic osteolysis and subsequent asceptic loosening.5 Wear and subsequent debris that it produces initiate synovitis and foreign-body reaction, which can ultimately lead to severe bone loss.
Polyethylene wear is more frequently seen in weight-bearing joint replacements such as knees and hips due to weight-bearing stresses. It is diagnosed when asymmetric joint space narrowing is present on radiographs. Polyethylene wear of shoulder replacements is rarely demonstrated on radiographs.
AP radiograph of both knees. The right knee has marked joint space narrowing worse in the medial compartment with metal-on-metal contact, consistent with polyethylene wear.
Knee polyethylene spacer demonstrating central wear down to the underlying metal backing.
Glenoid polyethylene component demonstrating eccentric wear (arrow).
Polyethylene Cup Dislocation
Rarely, polyethylene components may dislodge from the glenoid and dislocate into the surrounding soft tissues. Polyethylene cups have low density on radiographs which allows for identification. CT or arthrography may be necessary to confirm diagnosis.
Transcapular Y view demonstrates dislocated polyethylene component with its cement backing (arrows).