Metal on metal total hip arthroplasty (MoM THA) provides the potential improvement in articular wear. However, several adverse events including pseudotumor had been reported. Magnetic resonance imaging (MRI) was considered to be the proposal tool for detection of pseudotumor after MoM THA. In this study, we performed the screening of pseudotumor after MoM THA using the MRI.

We studied 43 patients with M2a Magnum® (Biomet) and 34 patients with M2a Taper® (Biomet) of MoM THA from December 2009 to December 2011 with follow-up of 2.5 years (2.0–4.0 years) after surgery. MRI assessments were performed at a mean of 2.1 years postoperatively. Pseudotumor findings were graded using Anderson classification (Skeletal Radiol, 2011: 40; 303). Age, sex, height, weight, Harris Hip Score, EQ5D satisfaction score, UCLA activity score, and blood metal ion levels were evaluated.

The prevalence of pseudotumor was 27.2%; 56 normal (Type A), 13 mild (C1), 8 moderate (C2) and none were graded severe (C3). Weight and BMI in the mild group was significantly higher than those in normal. There was no significant difference in age, sex and height among these groups. With regard to Harris Hip score, pain and ROM score in moderate group was significantly lower than that in normal and mild group. EQ5D satisfaction score and UCLA activity score showed not significant differences among groups. 3.01±3.32 μg/L of blood cobalt ion levels in the moderate groups was significantly higher than 0.97±0.64 μg/L in normal group. Blood cobalt ion levels of 1 mild and 2 moderate were over the threshold of 7 μg/L. These patients were implanted with M2a Taper, not M2a Magnum. 14% of the prevalence in the patients with M2a Magnum was significantly lower than 41% in the patients with M2a Taper. No revision surgeries were required.

The patients with no pseudotumor did not show the increase of blood metal ion. Contrarily, several patients showed the increase of blood metal ion in case of detecting pseudotumor. MRI assessments were useful for screening of pseudotumor after MoM THA and blood metal ion should be investigated for patients with mild and moderate pseudotumor in MoM THA.

Metal on metal total hip arthroplasty provides the potential improvement in articular wear and the use of large-diameter femoral heads following the prospect for reduction in the risk of dislocation. The purpose of this study was to compare the clinical and radiographic outcomes as well as serum metal ion level between the two different component designs with small and large femoral heads in metal on metal total hip arthroplasty.

We studied 39 patients with large head (Magnum®, Biomet; cup size minus 6 mm) and 37 patients with small head (M2a taper®, Biomet; 28 or 32 mm head) of metal on metal total hip arthroplasty between December 2009 to October 2011 with follow-up of 2.1 years (1.0–3.3 years) after surgery. Harris Hip Score, UCLA activity score, EQ-5D, radiographic assessment, and serum cobalt and chromium ion levels were evaluated.

Harris Hip Score, UCLA activity score, and EQ-5D were improved after surgery in small and large head groups, however, no significant differences were observed between both groups. Cup inclination was below 50 degree in all prosthesis. No loosening and no osteolysis were observed. Cobalt and chromium ion was not detected before surgery; however, metal ion levels of both groups were increased after surgery in time dependent manner. There was no significant difference between two groups at one year after surgery. One patient in each group showed the increase of cobalt ion level over 7 ppb (15.4 ppb, 12.9 ppb) without any clinical symptom including pain. Cup inclination was 29 degree in both patients and cup anteversion was 38 and 41 degree, respectively.

There was no significant difference of ion levels between both groups. No dislocation was observed in large head group while one dislocation occurred in small head group. No patients required the revision surgery.

This metal on metal component, especially with large femoral heads, showed the good clinical results at the maximum follow up of 3.3 year after surgery. However, the ion level of two patients increased over 7 ppb and longer follow-up will be needed.