Abstract
Introduction
Modular femoral necks have shown promising clinical results in total hip arthroplasty (THA) to optimize offset, rotation, and leg length. Given the wide variety of proximal femoral morphology, fine-tuning these kinematic parameters can help decrease femoroacetabular impingement, decrease wear rates and help prevent dislocations. Yet, additional implant junctions introduce additional mechanisms of failure. We present two patients who developed an abnormal soft tissue reaction consistent with a metal hypersensitivity reaction at a modular femoral neck/stem junction requiring revision arthroplasty.
Methods
Two patients underwent THA for primary osteoarthritis with the same series of components: 50 mm shell, a 36 mm highly-crosslinked polyethylene liner, uncemented titanium alloy modular stem with a 130 degree Cobalt Chromium (CoCr) modular femoral neck, and 36 mm CoCr head with a +5-mm offset. Patient 1 was a 63 year-old female who had an uneventful post-operative course but presented seven months later with progressive pain in the left hip. Patient 2 was an 80 year-old female who did well post-operatively, but presented with limp and persistent pain at 10 months post-op.
An initial evaluation of a painful THA to rule out aseptic loosening, infection, mal-positioning, loosening and osteolysis included radiographs, lab work (CBC, ESR, CRP, Cobalt & Chromium levels) and Metal Artifact Reduction Sequence (MARS) MRI.
Results
Elevated ion levels (Table 1) and Metal Artifact Reduction Sequence (MARS) MRI were consistent with an abnormal soft tissue reaction. A histological analysis of operative specimens displayed extensive necrosis and lymphocytosis, consistent with the diagnosis of metal hypersensitivity reactions (MHSR). Both patients underwent debridement and revision femoral arthroplasty with non-modular counterparts of the original femoral implant and have been asymptomatic post-operatively at greater than 1 year follow-up.
Discussion
MHSR reactions are primarily described in the setting of metal on metal articulations of the head and acetabulum in THA and hip resurfacing. These reactions have not been reported at the modular neck/stem junction. Although modular necks show promise in THA, the advantages of increased component modularity must be carefully weighed against the risks of mechanical wear and subsequent MHSR and/or component failure.
