Body mass index and acetabular component position in total hip arthroplasty

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.