Imaging evaluation of polyethylene liner dissociation in total hip arthroplasty.

OBJECTIVE

To describe the imaging findings of polyethylene liner dissociation in total hip arthroplasty.

MATERIALS AND METHODS

Retrospective search of our institution's radiology database identified 12 patients with polyethylene liner dissociation of a total hip arthroplasty. Clinical and operative notes were reviewed. All radiological studies were reviewed independently by two radiologists.

RESULTS

Among 12 patients (seven females/five males; mean age: 67 years; median interval after surgery at diagnosis: 8.5 months) with polyethylene liner dissociation, 11 had radiographs, six had CT, seven had MRI, and two had arthrography. "Bubble sign" and "crescent sign" on radiography were insensitive, seen only in three patients, but all showed abrupt eccentric positioning of the femoral head. CT identified the dislocated liner in five of six patients but failed to identify one liner, which was partially associated with the acetabular cup. MRI identified the dislocated liner in all seven patients, with the MAVRIC (multiacquisition variable resonance image combination) sequences either increasing the diagnostic confidence relative to the routine pulse sequences or being the sole sequences in which the liner can be identified if the liner remained partially associated with the acetabular cup. Arthrography identified the dislocated liner in one of two patients.

CONCLUSIONS

Previously described radiographic signs of polyethylene liner dissociation are insensitive, but abrupt eccentric positioning of the femoral head in the correct clinical context is highly suggestive of the diagnosis. MRI and CT can accurately localize the displaced liner. MAVRIC is particularly helpful if the dislocated liner remains partially associated with the acetabular cup.