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  • Title: Proximal component modularity in THA--at what cost? An implant retrieval study.
    Author: Kop AM, Keogh C, Swarts E.
    Journal: Clin Orthop Relat Res; 2012 Jul; 470(7):1885-94. PubMed ID: 22048865.
    Abstract:
    BACKGROUND: While modular femoral heads have been used in THA for decades, a recent innovation is a second neck-stem taper junction. Clinical advantages include intraoperative adjustment of leg length, femoral anteversion, and easier revision, all providing flexibility to the surgeon; however, there have been reports of catastrophic fracture, cold welding, and corrosion and fretting of the modular junction. QUESTIONS/PURPOSES: We asked whether (1) the neck-stem junction showed the same degradation mechanisms, if any, as the head-neck junction, (2) the junction contributed to THA revision, (3) the alloy affected the degree of degradation, and (4) the trunion machine finish affected the degradation mechanisms. METHODS: We compared 57 retrievals from seven total hip modular designs, three cobalt-chromium-molybdenum and four titanium based: Bionik(®) (four), GMRS(®) (four), Margron(®) (22), Apex(®) (five), M-series(®) (five), ZMR(®) (two), and S-ROM(®) (15). Macroscopic inspection, microscopy, and micro-CT were conducted to determine the effects of materials and design. RESULTS: The cobalt-chromium-molybdenum components showed crevice corrosion and fretting of the neck-stem taper, whereas the titanium components had less corrosion; however, there were several cases of cold welding where disassembly could not be achieved in theater. CONCLUSIONS: Even with modern taper designs and corrosion-resistant materials, corrosion, fretting, and particulate debris were observed to a greater extent in the second neck-stem junction. Titanium-based modular arthroplasty may lessen the degree of degradation, but cold welding of the components may occur. CLINICAL RELEVANCE: Degradation of the second junction contributed to 8 cases of metallosis and two cases of aseptic lymphocyte-laminated vascular-associated lesions contributing to revision.
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