Abstract
Metal-on-metal articulations are increasingly used in THR. Hypersensitivity reactions to the metal ions can occur. The symptoms and signs are similar to a patient presenting with an infected prosthesis. Correct diagnosis before revision surgery is crucial to implant selection and operation planning. We present a practical approach to this diagnostic problem.
The history, clinical findings, hip scores, radiology, serum metal ions, ESR, C-RP, hip arthroscopy and aspirate results, synovial fluid metal ion levels, labelled white cell/colloid scan, 99m-technetium scan, revision hip findings and histology of a typical patient who had an allergic response to a metal-on-metal hip articulation are presented, and how the findings differ from a patient with an infected implant. Clinical examination, hip scores and serum metal ion levels were repeated one year after revision of the metal-on-metal hip articulation to a ceramic-on-ceramic.
In hypersensitivity, the periarticular tissues undergo lymphocyte-dominated infiltration, the histology differs from that found in infection. The white cell labelled/colloid scan also uses this difference for diagnosis. Hip aspiration is the single best investigation for infection.
Conclusion: There is no single investigation available in most hospitals that will reliably differentiate infection from allergy in the painful THR. Hip aspiration, labelled white cell/colloid scan and histology obtained from hip arthroscopy biopsy are the most useful investigations.
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