Abstract
Background
Metal-on-metal hip implants can produce adverse tissue reactions to wear debris. Increased metal ion concentrations in the blood are measured as a proxy to wear and the complications it can trigger. Many studies have examined various factors influencing the metal ion concentrations. This is the first study to investigate the effect of physical activity level, as objectively measured in daily life, on blood ion levels, expecting higher concentrations for higher patient activity.
Methods
Thirty-three patients (13F/20M, 55.8 ± 6.2 years at surgery) with a unilateral resurfacing hip prosthesis were included. At last follow-up (6.8 ± 1.5 years) cobalt and chromium concentrations in the blood were determined by inductively coupled plasma mass spectrometry. Physical activity was measured during 4 successive days using a 3D-acceleration-based activity monitor. Data was analysed using validated algorithms, producing quantitative and qualitative parameters. Acetabular cup position was measured radiographically. Correlations were tested with Pearson's r'.
Results
Wide ranges in cobalt (10-833nmol/l) and chromium (16-592nmol/l) concentrations were measured. No correlations were found between metal ion concentrations and patient characteristics. The mean time of walking per day of was 5475 ± 2730 seconds (≈ 91 minutes) per day, with 6953 ± 3104 steps made during the day. The cadence, the number of steps per minute, was 99.5 ± 7.4. The subjects performed 41 ± 13 sit-stand transfers per day. The number of peak intensity declines when peaks where more intense. No correlations were found between quantitative or qualitative parameters and metal ion concentrations
Conclusions
Higher metal ion concentrations were not correlated with higher activity levels contrary to original expectations. Based on the results the orthopaedic surgeons is able to reassure his or her patients that physical activity in daily living is presumably safe en does not influence metal ion concentrations
Level of Evidence
2b
Approval
the ethics committee of the Atrium MC, Heerlen approved this study.
