Mid-Term Functional Outcomes & Cobalt Chromium Levels Following Ceramic on Metal Total Hip Replacement

Nisarg Mehta, Justin Leong, Philip Brown, Dhawal Patel, Hussain Kazi , Fintan Adrian Carroll

Background: With controversies surrounding Metal on Metal (MoM) total hip arthroplasty (THA); alternate bearing surfaces such as Ceramic on Metal (CoM) had a surge in popularity. However, there are reports of higher than expected rate of revision and elevated serum metal ions and radiolucent lines (RLL) at mid-term follow-up. The aim of this study was to report functional & radiological outcomes of CoM THAs performed at our institution.

Methods: Patients undergoing CoM THA between 2008 and 2010 were identified and brought back for followup in 2017 where up-to-date radiographs, Oxford Hip Scores & Cobalt Chromium levels were taken. The primary outcome measure was mean oxford hip score at follow-up. Secondary outcome measures included serum cobalt chromium levels & revision surgery.

Results: A total of 114 CoM THAs were performed on 94 patients with a mean follow-up of 76.8 months (0-120) and a median age of 58 (42-70). The mean socket size was 54mm (42-70), median femoral head size was 36mm (28-36) & mean inclination was 42.3 0 (31 0 -61 0 ). There was a significant improvement between preoperative & mean follow-up oxford hip scores [Preoperative 14.6 (2-36), Follow-Up 45.7(32-48) p<0.001]. Of the 83 patients that survived the mean serum cobalt and chromium levels were 41nmol/L (3-678) & 41nmol/L (0-196). 13 patients had radiolucent lines >1mm in at least 1 Gruen Zone. 98% of patients have well-functioning hips at follow-up with 2 patients undergoing revision with pain & elevated metal ion levels above MHRA thresholds.

Conclusions: Majority of patients with CoM THAs remain asymptomatic and have good functional outcomes at mid-term follow-up. However, we note higher than expected serum metal ion levels and presence of RLL in certain patients

Implications: Despite having high functioning hips, all patients with CoM THAs should be followed-up long term with annual radiographs and serum metal ion levels


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