Review Question - QID 4832

Figure A shows a left total hip arthroplasty with eccentric polyethylene wear. Figure B shows that her left hip was revised to a constrained acetabular liner, most likely a result of recurrent instability.

Revision strategies for hip instability are typically directed at correcting the underlying cause of instability. For example, instability most commonly occurs as a result of poor implant design, positioning or loosening, or the loss of soft-tissue function or tensioning. Operative strategies are designed to correct these etiologies by repositioning or exchanging components, integrating modular designs and improving soft tissue tensioning, etc. Constrained acetabular liners are often used in conjunction with these modalities to address the problem of recurrent instability relating to soft tissue deficiency and dysfunction in the affected hip.

Alberton et al. retrospectively reviewed 1548 revision arthroplasties for the incidence of dislocation. They found the overall dislocation rate to be 7.8%. Factors contributing to increased dislocations were found to be trochanteric non-unions, femoral heads <28mm in diameter and extensive soft-tissue dissection. Protective factors were modular acetabular components or liners, larger femoral heads >28mm and re-establishing abductor tensioning.

Paterno et al. retrospectively reviewed 438 primary and 181 revision total hip arthroplasties for patient factors contributing to dislocation. They found an overall dislocation rate of 6%. 23% of patients with a history of excessive intake of alcoholic beverages (more than six ounces a day) had at least one dislocation. There was no relationship between the variables of age, gender, obesity, or preoperative diagnosis and the incidence of dislocation.

Figure A shows bilateral primary cementless, nonconstrained total hip replacements. The left hip shows eccentric femoral head placement within the acetabulum indicative of eccentric polyethylene wear. Figure B shows the conversion to a constrained, dual-mobility, polyethylene liner. The overall metal component position appears satisfactory.

Incorrect Answers:
Answer 1: There is no radigraphic finding of fracture. In addition, acetabular fractures would not be treated with conversion to a constrained liner.
Answer 2,3: The presence of osteolysis in the femoral and acetabular components is not significant based on these radiographic images.
Answer 5: There is no valgus malalignment of the left femoral implant.