Contact patch to rim distance predicts metal ion levels in hip resurfacing.

BACKGROUND: Component design, size, acetabular orientation, patient gender, and activity level have been suggested as factors leading to elevated metal ion concentrations after-on-metal hip resurfacing arthroplasty (MMHRA). The calculation of the contact patch to rim (CPR) distance integrates component size, design, and acetabular orientation and may be a good predictor of elevated metal ion levels. QUESTIONS/PURPOSES: We evaluated the effects and the predictive value of the CPR distance on serum cobalt (CoS) and chromium (CrS) ion levels. METHODS: We retrospectively studied 182 patients with Conserve Plus MMHRAs at a minimum of 12 months after surgery (median, 57 months; range, 12-165 months). CoS and CrS levels were analyzed using inductively-coupled plasma mass spectrometry. Multiple logistic regression was performed to determine which if any of the factors related to serum ion levels. RESULTS: Patients with CPR distances of 10 mm or less had a 37-fold increased risk of having elevated CoS of 7 µg/L or higher. Similarly, these patients had an 11-fold increased risk of having elevated CrS of 7 µg/L or higher. Sex and University of California Los Angeles activity scores did not influence the postoperative CoS and CrS levels. The negative predictive value for CPR distance less than 10 mm was 99.3% for CoS greater than 7 µg/L and 98.0% for CrS greater than 7 µg/L. CONCLUSIONS: Our observations suggest the CPR distance would be a useful indicator to determine which patients are at risk for elevated ion levels. Patients with CPR distances greater than 10 mm need not be monitored unless they become symptomatic.

Metal ion levels in total hip arthroplasty versus hip resurfacing.

Recent studies suggest that the tapered interface between stem and femoral head may be a substantial source of cobalt and chromium ion release after metal-on-metal (MOM) total hip arthroplasty (THA). This study compared patient ion levels after MOM hip resurfacing (HR) and MOM THA performed with identical acetabular components. 110 HRs were compared with 22 THAs. All had well-oriented components, unilateral implants, and serum ion studies beyond one year post-operatively. The HR group's median cobalt value was 1.11 µg/L vs. 2.86 µg/L for the THA patients. The HR group's median chromium value was 1.49 µg/L vs. 2.94 µg/L for THA. Significantly higher THA ion levels suggest a source of ions other than the MOM bearing itself.

Mid-to-long term follow-up of Transcend metal-on-metal versus Interseal metal-on-polyethylene bearings in total hip arthroplasty.

Second-generation metal-on-metal total hip arthroplasty (THA) was introduced in the early 1990s to address osteolysis and aseptic loosening resulting from polyethylene wear. We present a comparison between the Transcend metal-on-metal and Interseal metal-on-polyethylene THAs. Thirty-seven hips with Transcend metal bearings and 36 hips with Interseal polyethylene acetabular liners but identical acetabular shells were reviewed to determine clinical performance, radiographic changes, and survivorship. Patients with higher anticipated activity levels were selected to receive the Transcend bearing. Mean follow-up time was 107.0 months for the Transcend group, and 90.4 months for the Interseal group. There were no significant differences between the Transcend and Interseal groups for mode of failure and survivorship, which is notable considering the younger and more active Transcend group. However, the Transcend group showed significantly better clinical scores, which may have been a result of the selection methods. Neither surface was differentially implicated in osteolysis, aseptic loosening, or adverse local tissue reaction (ALTR). Our study shows a favorable and comparable performance for both systems.