Mid Term Results of Ceramic on Metal Bearing in Comparison to Metal on Metal Bearing in Total Hip Arthroplasty

Introduction: Hard on hard bearings were thought to be a good option for young, active patients.
Ceramic on metal (CM) bearings were introduced to overcome both metal on metal (MM) and ceramic on ceramic (CC) complications.
Few clinical studies examined this new bearing and only short term results are available.

Methodology: We compared the midterm results of 47 patients (50 hips) with CM to 64 patients (66 hips) with MM between November 2009 and December 2011.. The patients received either a 36 mm ceramic or a 36 mm metallic femoral head. All received an acetabular metal liner of 36 mm inner diameter. Functional assessment of the hips was determined with Harris Hip (HHS) and UCLA scores. Blood cobalt (Co) and chromium (Cr) levels were measured. Inclination and anteversion of the acetabular cup were assessed with Einzel-Bild-Roentgen-Analyse (EBRA) software on the last radiographic evaluation.

Results: Mean age at the time of surgery was 57 years (range 44 to 75) for CM group and 60 years (range 30 to 77) in MM group. Mean follow up was 50.4 months (28.92 to 68.76 months). The mean HHS score was 90.2 and 90.8 in the CM and MM group, respectiveyl. Mean UCLA was 6.2 in MM group and 6.4 in the CM. The mean metal ion levels (Co and Cr) were significantly less in the CM group with 1.3 and 0.2 m/L versus the MM group (3.35 and 1.54 m/L respectively). One MM patient has been revised for pseudotumor. In this case, femoral neck impingement on the cup rim was identified intra-operatively during extreme extension.. None of the CM group needed revision or developed pseudotumor.

Conclusion: Good function, diminished metal ion release and lower complication rates in the CM group compared with MM, suggest that the CM bearing is associated with decreased adverse effects.