Abstract
Purpose: Articular surface replacement (ASR) is an alternative for young patients considered for hip replacement. The in vivo release of ions from these surfaces has yet to be well evaluated. The purpose of the present study was to compare the concentrations of metal ions in blood of patients with ASR and metal-on-metal (MM) total hip arthroplasty (THA).
Methods: Blood was collected 6 months after implantation time into Sarstedt Monovette® tubes for trace metal analysis from patients having ASR (n=61), 28 mm-head MM THA (n=18), and 36 mm-head MM THA (n=25). The concentrations of cobalt (Co), chromium (Cr), and molybdenum (Mo) were analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS).
Results: The median Co level was not significantly different between the 3 groups (2.35 ppb, 2.00 ppb, and 2.50 ppb for the 28 mm MM THA, 36 mm MM THA, and the ASR patients, respectively). The median Cr level was significantly lower in the 36 mm MM THA patients (0.10 ppb) compared to the 28 mm MM THA (0.15 ppb) and the ASR (0.40 ppb) patients. The median Mo level was significantly lower in the 36 mm MM THA patients (1.30 ppb) compared to the 28 mm MM THA (2.00 ppb) and the ASR (1.50 ppb) patients.
Conclusions: Our results show that the level of ions in 36 mm MM THA patients was lower than in 28 mm MM THA patients. This can be explained by the fact that 28 mm MM bearings are resistant to microseparation during the normal gait cycle, which is theoretically accompanied by a reduction of fluid film lubrication and increased potential for the production of wear debris. Our results also show that the ion levels in patients having ASRs is similar to that observed in 28 mm MM THA patients but higher than in 36 mm MM THA patients. The diametric clearance of ASRs is typically much greater and the potential for a ‘suction fit’ may be less, leading to higher ion production. The concentration of ions in long-term follow-up remains however to be elucidated. Funding: Educational Grant from the Canadian Orthopaedic Foundation
Correspondence should be addressed to Cynthia Vezina, Communications Manager, COA, 4150-360 Ste. Catherine St. West, Westmount, QC H3Z 2Y5, Canada
