Abstract
Introduction
The use of metal-on-metal (MOM) and modular total hip arthroplasty (THA) is associated with potentially serious complications including elevated serum metal ion levels, pseudotumor, cardiomyopathy and neurologic abnormalities. The primary aim of this analysis was to identify any associations between the presence of pseudotumor, serum metal ion levels, and specific dual modular implant components.
Methods
We evaluated prospectively collected data from 49 patients, mean age 58.4 years, who underwent implantation of modular THA from 01/2004-01/2010. The collected data spanned a 5–11 year period from the time of index procedure. Serum metal ion levels, including titanium, cobalt and chromium, were collected in 2012 and 2015. Hip ultrasounds were performed on each patient by a trained musculoskeletal radiologist for evaluation of the presence of soft-tissue pseudotumor. Univariate nonparametric tests were used to compare the two groups: Fisher's exact tests for categorical variables, and Wilcoxon two-group tests for continuous variables. For the purposes of analysis, values that were below the level of detection (LOD) were set to half the LOD. All analyses were performed using SAS 9.4 (SAS Institute Inc, Cary, NC, USA). Statistical significance is set at p<0.05.
Results
Eight of 49 patients (16.3%) had pseudotumors on ultrasound examination. The average size measured 35.05 cm3 (7.35 cm3 – 130.81 cm3). In patients without pseudotumor, the serum levels (ng/mL) of titanium, cobalt and chromium were 3.2 ± 2.7, 4.4 ± 5.7 and 3.4 ± 4.9 in 2012 and 3.6 ± 4.9, 11.3 ± 33.7 and 5.3 ± 10.8 in 2015, respectively. Patients with pseudotumor had titanium, cobalt and chromium levels of 3.5 ± 2.3, 8.4 ± 8.7 and 6.2 ± 9.4 in 2012 and 4.1 ± 3.4, 6.0 ± 4.5 and 5.1 ± 6.4 in 2015. The ratio of cobalt to chromium was 1.6 ± 1.3 in 2012 and 1.8 ± 1.2 in 2015 in patients without pseudotumor and 2.1 ± 1.2 and 1.9 ± 1.3 with patients with pseudotumor, respectively. There was no statistical correlation between the presence of pseudotumor and age, component pairings (stem, neck and cup) and any of the serum metal ion levels.
Discussion/Conclusion
In this prospective cohort study the incidence of pseudotumor was 16.3% in asymptomatic patients with modular THA. The presence of pseudotumor did not correlate with component pairings, serum metal ion levels or cobalt to chromium ratios.
