|Beitragstitel||Predictors and patterns of elevated blood metal ions levels after metal-on-metal total hip arthroplasty|
Risk factors for elevated blood metal ion levels have been reported after large metal-on-metal (MoM) total hip Arthroplasty (THA). However, the literature on risk factors after small head MoM THA is sparse and little is known about the pattern of blood ion levels over time. Our objectives were to determine predictors of elevated blood metal ion levels after small head MoM THAs and to assess the pattern of blood metal ion levels in both small and large head THAs over time.
All primary MoM THAs with postoperative blood metal ion (cobalt and chromium) concentration performed between 11/1998 and 03/2010 were included. The cut off for blood cobalt level considered as elevated was ≥ 2ug/l. We stratified the MoM THAs in 2 groups, small (≤ 28mm) vs. large (>28mm) head THAs. The following potential predictors were evaluated: age, sex, BMI, smoking status, ASA score, Charnley score, aspirin use, diagnosis, bilateral MoM THA, stem type (cemented vs. not), side operated, cup diameter and inclination. To assess the pattern of blood metal ion levels over time, only unilateral MoM THA with at least two cobalt measurements were included. Logistic regression was used for the analysis.
Overall, 447 MoM THAs were included (mean age 58.5 years, 44.5% women), 355 with small heads (group 1) and 92 with large heads (group 2). Group 1 was older (mean age 61.1 years vs. 48.7) and included more women (49% vs. 28%). Median cobalt value at first measure was 1.2 ug/l (interquartile range, IQR, 0.8-1.9) for group 1 and 2.2 ug/l (IQR 1,2-6.1) for group 2. In the univariate analysis female gender, never-smoking, ASA 3-4, bilateral MoM THA and aspirin use were significantly associated with increased cobalt levels in the small head group. In the multivariate analysis bilateral MoM THA, never-smoking, aspirin use, and ASA 3-4 remained significant predictors (p< 0.2). 48 unilateral THAs had a second cobalt measure. Cobalt level was ≥ 2ug/l in 8 patients (23.6%) in the small and 9 (64%) in the large head group. Overall 6 patients changed the category (< vs. ≥ 2ug/l), 5 moved to above and one moved to below 2ug/l, while in 41 THAs (85.4%) cobalt levels remained stable.
Bilateral MoM THA, aspirin use and higher ASA score were associated with higher cobalt levels in the small head MoM group. Ever-smoking was associated with lower cobalt levels. The patterns of cobalt levels appeared to be stable in a high proportion of THAs after 5 years postoperative.