Abstract
Polyethylene and femoral head exchange for wear or osteolysis is a common operation. The difficulty lies in the facts that wear and osteolysis are difficult to measure, wear does not always correlate with osteolysis, catastrophic failure (wear through, loosening, or fracture) is difficult to predict, and these problems are usually asymptomatic.
I currently recommend this procedure when complete wear through of the polyethylene is present or impending, when the patient has obvious wear and symptoms, or if there is a rapidly enlarging osteolytic lesion.
The surgical goals focus on management of debris generation and management of the osteolytic lesion. A third goal becomes avoidance of the know complications of this procedure. Management of debris generation basically involves modernising the head and polyethylene. Management of the osteolytic lesion includes debridement and when possible grafting. By far the most common complication after this procedure is dislocation. Prevention of dislocation should be accomplished by patient education, use of larger heads when possible, and capsular repair.
Prerequisites to perform this procedure are a replacement liner of adequate thickness that can be locked or cemented in place. The acetabular component must be stable. Lastly the component must be properly oriented to minimise both wear and dislocation.
Metal-on-metal liner exchanges
Metal-on-metal liner conversion to metal-on-poly is becoming more common. Since patient satisfaction with THA is high, MoM patients may unknowingly minimise their symptoms because they are minor compared to the symptoms before surgery. The patient history should include specific questions about groin pain, swelling, hip noise, and asking the patient if they notice their hip on a daily basis. Patient symptoms, osteolysis and a pseudotumour are indications for modular conversion. Radiographically stable, well-oriented components that can accept a polyethylene liner are requirements for a successful conversion.
