Comparison of whole-blood metal ion levels in four types of metal-on-metal large-diameter femoral head total hip arthroplasty: the potential influence of the adapter sleeve.

BACKGROUND: Metal-on-metal bearings, as used in total hip arthroplasty prostheses that have a large-diameter femoral head, were proposed as an option for treating young and active patients with degenerative hip disorders. Despite the theoretical improved performance of large metal articulations with regard to wear, metal ion levels produced by total hip arthroplasty prostheses in which a large-diameter femoral head is used have not been thoroughly evaluated. METHODS: From 173 eligible patients, 144 patients were allocated to undergo a unilateral total hip arthroplasty with use of metal-on-metal components and a large-diameter femoral head. The purpose of this study was to compare the amount of metal ion release (chromium, cobalt, and titanium) from four different types of prostheses from four different implant manufacturers (Biomet, DePuy, Smith & Nephew, and Zimmer). RESULTS: For cobalt ion levels, a significant difference was found between the different types of total hip arthroplasty prostheses with a large-diameter femoral head at three, six, twelve, and twenty-four months, but only in male patients or patients with a femoral head size of 50 mm or greater. The highest mean cobalt levels at all follow-up periods were observed with the Zimmer implant and the lowest with the Biomet implant. Titanium ion levels were highest in the Zimmer group at all follow-up periods, whereas no difference between groups was found for chromium. At the most recent follow-up, one hip was revised after the development of an adverse local tissue reaction. Of concern was the observation at the time of revision surgery of black metallic deposits inside the adapter sleeve and on the prosthetic femoral neck. CONCLUSIONS: This investigation revealed that metal ion release differs greatly between various total hip arthroplasty implants with a large-diameter femoral head. The sources of metal ion production are numerous, but it is hypothesized that wear and corrosion at the junction between the adapter sleeve and the femoral stem in some patients may be responsible for the elevated cobalt ion levels that were found in the Zimmer group. On the other hand, an adapter sleeve made of titanium, such as the one used with the Biomet large-diameter-head total hip arthroplasty, is an unlikely contributor to the release of cobalt ions. Current technology or design of some total hip arthroplasty systems that make use of a large-diameter femoral head may not yet allow the use of modular large heads with a metal-on-metal articulation, especially in young, active male patients whose activities generate high loads at the hip joint. Further research is needed to better understand the favorable design characteristics of modular junctions in metal-on-metal total hip arthroplasty implants that make use of large-diameter femoral heads.

Metal Ion release with large-diameter metal-on-metal hip arthroplasty.

Preoperative and postoperative ion concentrations were measured in 29 metal-on-metal, large-diameter head total hip arthroplasty (LDH-THA) patients. Mean chromium, cobalt (Co), and titanium levels from LDH-THA were 1.3, 2.2, and 2.7 µg/L at 12 months. The open femoral head design showed significantly higher Co concentrations than the closed design (3.0 vs 1.8 µg/L, P = .037). Compared with previously published ion levels from a hip resurfacing system presenting the same bearing characteristics, Co levels were significantly higher in LDH-THA (2.2 vs 0.7 µg/L, P < .001). This study has demonstrated that the addition of a sleeve with modular junctions and an open femoral head design of LDH-THA causes more Co release than bearing surface wear (157% and 67%, respectively). Even if no pathologic metal ion threshold level has been determined, efforts should be made to minimize its release. We recommend modification or abandonment of the modular junction and femoral head open design for this specific LDH-THA system.