Body mass index and acetabular component position in total hip arthroplasty

Abstract

INTRODUCTION: Correct acetabular component positioning during total hip arthroplasty affects the restoration of normal biomechanics, component wear and failure rates. This study examined whether a patient's body mass index (BMI) affects the accuracy of acetabular component placement in terms of the post-operative abduction angle. METHODS: This was a retrospective review of 102 total hip arthroplasties performed from May 2009 in a single institution. The acetabular abduction angle was measured on the post-operative radiographs of the included patients. Statistical analysis of variance and t-tests were performed using Microsoft Excel to compare the mean abduction angles of patients grouped according to their BMI. RESULTS: Comparison of the mean abduction angle between those with BMI < 25 and BMI > 25 showed a statistically significant difference (P = 0.003). Analysis of variance between all BMI groups was statistically significant (P = 0.01). Patients in the lowest centile of abduction angle had an average BMI of 28. Patients in the highest centile of abduction angle had an average BMI of 33. DISCUSSION: This study shows that patients with a normal BMI tend to have smaller abduction angles. Overweight or obese patients, on average, have a normal abduction angle but are more likely to have an 'open cup'. A number of factors unique to obese and overweight patient may contribute to an 'open cup' and less accurate cup placement.