Does body mass index affect the outcome of unicompartmental knee replacement?

Obesity is considered to be a contraindication for unicompartmental knee replacement (UKR). The aim was to study the impact of BMI on failure rate and clinical outcome of the Oxford mobile bearing UKR.

Two thousand four hundred and thirty-eight medial Oxford UKRs were studied prospectively and divided into groups: BMI < 25 (n = 378), BMI 25 to < 30 (n = 856), BMI 30 to < 35 (n = 712), BMI 35 to < 40 (n = 286), and BMI 40 to < 45 (n = 126) and BMI ≥ 45 (n = 80).

There was no significant difference in survival rate between groups. At a mean follow-up of 5 years (range 1–12 years) there was no significant difference in the Objective American Knee Society Score between groups. There was a significant (p < 0.01) trend with the Oxford Knee Score (OKS) and Functional American Knee Society Scores decreasing with increasing BMI. As there was an opposite trend (p < 0.01) in pre-operative OKS, the change in OKS increased with increasing BMI (p = 0.048). The mean age at surgery was significantly (p < 0.01) lower in patients with higher BMI.

Increasing BMI was not associated with an increasing failure rate. It was also not associated with a decreasing benefit from the operation. Therefore, a high BMI should not be considered a contra-indication to mobile bearing UKR.

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