Abstract
Purpose
Our primary purpose was to study the rate of occurrence and the natural course of pseudotumors in patients who had not required a revision procedure. Our secondary purpose was to see if there is a relationship between serum metal ion analysis and clinical symptoms with metal-on-metal (MOM) hip arthroplasty.
Patients and Methods
We used repeated metal artifact reduction sequence (MARS) magnetic resonance imaging (MRI) to screen 17 unrevised hips (mean patient age 63.0 years, 43 to 83 years) with pseudotumors and 26 hips (mean patient age 63.2 years, 47 to 83 years) without pseudotumors. Patients with 17 MOM, 17 ceramic-on-polyethylene (COP) and 7 ceramic on ceramic (COC) who had undergone repeated MARS MRI were evaluated with or without any symptoms. We utilized MARS MRI to score the type of pseudotumors using the Hart method. The mean post-operative time to the first MARS MRI scan was 30.0 months (8 to 96), and the time between the first and the second MARS MRI scan was eleven months (6 to 12). Serum Cr and Co ion measurements were undertaken at the time of both MRIs and analyzed only after MOM total hip arthroplasty.
Results
The rate of occurrence of pseudotumors was 47.5% with MOM, 33.0% with COP, and 25.0% with COC. There was a significant difference in number of abnormalities between MOM and COP and COC bearing. At the second MRI scan, the grade of severity of pseudotumors had not changed in 40 hips. Two new asymptomatic pseudotumors (MOM:1 case, COP:1 case) were detected and one pseudotumor was downgraded. In 17 patients with pseudotumors, two cases (11.7%) were symptomatic and in 26 patients without pseudotumors, 4 cases (15.3%) were symptomatic, with no significance between the two groups. In 17 patients with MOM cases, only two cases with pseudotumors were symptomatic, and both cases showed elevated blood metal ion levels. However, in these series 13 cases (6 with pseudotumors and 7 without pseudotumors) (76.4%) were overtaken baseline. So there was no significance in terms of metal ion levels with or without pseudotumors.
Discussion
Overall, there was the same tendency in terms of occurrence of pseudotumors compared with our previous studies regarding MARS MRI. Pseudotumors can occur in patients with COP and COC bearing secondary to corrosion at modular femoral head neck taper. This feature is similar to pseudotumors seen in patients with a MOM bearing. In general, the characteristics of the pseudotumors hardly changed. Repeated MARS MRI scans within one year after total hip arthroplasty showed little or no variation. On the other hand, in 26 patients without pseudotumors, two new asymptomatic pseudotumors were detected. Moreover, there was no clinically useful association among symptoms, serological markers and the severity of MR findings. In conclusion, MRI abnormalities are present in normal asymptomatic THA and, regardless of the type of bearing surface, the occurrence of pseudotumors suggests that it might originate from head neck junction and indicate subclinical disease.
