Review Question - QID 220045

The patient has a painful metal-on-metal hip resurfacing implant with elevated serum metal ions and a pseudotumor. The acetabular component appears to be in a reasonable position. The most appropriate surgery for this patient is a revision of the femoral component to a femoral stem, and placement of a non-metal-on-metal bearing surface (e.g. ceramic on polyethylene).

Hip resurfacing arthroplasty is a bone-preserving procedure that is favorable in young male patients and utilizes metal-on-metal articulations. Metallosis is, therefore, a concerning complication of these implants and can result in pseudotumor formation and subsequent destruction of the hip abductors. Patients presenting with a painful prosthesis should be screened with metal ion levels as well as a metal artifact reduction sequence MRI. The treatment for this condition is to revise to a total hip arthroplasty with a non-metal-on-metal bearing surface

Kwon et al. performed a retrieval study in which they compared implants revised for pseudotumors to those revised for other reasons of failure. They found that the pseudotumor group had a higher rate of linear wear of the femoral component compared to the control group (8.1 microm/year vs 1.179 microm/year, p = 0.002), and acetabular component (7.36 microm/year vs 1.28 microm/year, p = 0.001). Wear of the acetabular component always involved the edge of the implant. They concluded that pseudotumor is associated with increased wear at the metal-on-metal articulation.

Bisschop et al. performed a prospective cohort study of 149 hip resurfacing patients. They found that 5.6% of patients required a revision due to a symptomatic pseudotumor. They found 28% of patients had a pseudotumor on CT, with 28% of these patients having complaints of groin pain, a mass, or paresthesia.

Figure A demonstrates a metal-on-metal hip resurfacing implant.

Incorrect answers:
Answer 1: There is low concern for infection in this case.
Answer 2: The hip resurfacing implant in Figure A has a metal-on-metal bearing surface.
Answer 3: Maintaining a metal-on-metal bearing surface in the presence of metallosis and a pseudotumor would not be appropriate.
Answer 4: The patient does not have instability and their abductors are intact. It is very unlikely they would require a constrained liner.