Original Questions
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Work-up of a painful metal-on-metal total hip arthroplasty demonstrated a large effusion on MRI. ESR and CRP were within normal limits. Metal ion levels were found to be highly elevated. Preoperative cell count demonstrated 917 WBCs and 51% PMNs and cultures were negative. Intra-op pathologic specimens demonstrated all areas <5 WBCs/HPF. Imaging demonstrated well fixed components with a vertically oriented acetabular cup and appropriately oriented femoral component. What is the likely best course of treatment?
- Total hip arthroplasty explant and placement of antibiotic spacer
- Femoral head and liner exchange to a ceramic on polyethylene bearing with retention of acetabular and femoral components
- Acetabular cup and femoral component revision
- Femoral component revision and conversion to a ceramic on polyethylene bearing with retention of acetabular cup
- Acetabular cup revision and conversion to a ceramic on polyethylene bearing with retention of femoral component
Discussion: Infection needs to be investigated, as a reason for MOM THA failure. However, one needs to be aware that distinction between septic failure and MOM-related failures can, at times, be difficult to differentiate. MOM reactions can mimic infection with elevated inflammatory markers (ESR and CRP), elevated synovial cell counts (need a manual count ordered) and effusions that grossly resemble purulent material.
With a stable ingrown cup that is malpositioned and with associated elevated metal ion levels, acetabular cup revision should be considered particularly with a vertical component as this can predict an increase in the risk of polyethylene liner edge-loading and ultimately early failure either via liner fracture or early liner wear from edge-loading.
Reference: Hsu AR, Kim JD, Fabi D, Levine BR. Adverse reactions in metal-on-metal total hip arthroplasty: two cases presenting as pseudoseptic acetabular component loosening. Am J Orthop (Belle Mead NJ). 2011 Oct;40 (10):509-513.