No association between serum metal ions and implant fixation in large-head metal-on-metal total hip arthroplasty.
BACKGROUND
The mechanism of failure of metal-on-metal (MoM) total hip arthroplasty (THA) has been related to a high rate of metal wear debris, which is partly generated from the head-trunnion interface. However, it is not known whether implant fixation is affected by metal wear debris.


METHODS
49 cases of MoM THA in 41 patients (10 women) with a mean age of 52 (28-68) years were followed with stereoradiographs after surgery and at 1, 2, and 5 years to analyze implant migration by radiostereometric analysis (RSA). Patients also participated in a 5- to 7-year follow-up with measurement of serum metal ions, questionnaires (Oxford hip score (OHS) and Harris hip score (HHS)), and measurement of cup and stem positions and systemic bone mineral density.


RESULTS
At 1-2 years, mean total translation (TT) was 0.04 mm (95% CI: -0.07 to 0.14; p = 0.5) for the stems; at 2-5 years, mean TT was 0.13 mm (95% CI: -0.25 to -0.01; p = 0.03), but within the precision limit of the method. For the cups, there was no statistically significant TT or total rotation (TR) at 1-2 and 2-5 years. At 2-5 years, we found 4 cups and 5 stems with TT migrations exceeding the precision limit of the method. There was an association between cup migration and total OHS < 40 (4 patients, 4 hips; p = 0.04), but there were no statistically significant associations between cup or stem migration and T-scores < -1 (n = 10), cup and stem positions, or elevated serum metal ion levels (> 7µg/L (4 patients, 6 hips)).


CONCLUSIONS
Most cups and stems were well-fixed at 1-5 years. However, at 2-5 years, 4 cups and 5 stems had TT migrations above the precision limits, but these patients had serum metal ion levels similar to those of patients without measurable migrations, and they were pain-free. Patients with serum metal ion levels > 7 µg/L had migrations similar to those in patients with serum metal ion levels < 7 µg/L. Metal wear debris does not appear to influence the fixation of hip components in large-head MoM articulations at medium-term follow-up.
Department of Orthopedic Surgery , Aarhus University Hospital, Aarhus , Denmark.
Mette Holm
MH
Hjorth
Kjeld
K
Søballe
Stig Storgaard
SS
Jakobsen
Nina Dyrberg
ND
Lorenzen
Inger
I
Mechlenburg
Maiken
M
Stilling
D015502:Absorptiometry, Photon; D000077:Acetabulum / Q000000981:diagnostic imaging / Q000601:surgery; D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects*; D005260:Female; D005500:Follow-Up Studies; D005548:Foreign-Body Migration / Q000097:blood / Q000000981:diagnostic imaging / Q000209:etiology*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D007477:Ions / Q000097:blood; D008297:Male; D008670:Metals / Q000009:adverse effects* / Q000097:blood; D008875:Middle Aged; D011475:Prosthesis Failure / Q000009:adverse effects*; D059869:Radiostereometric Analysis; D011795:Surveys and Questionnaires
D007477:Ions; D008670:Metals