Body mass index, hip function and surgeon volume are independent predictors of dislocation: an analysis of 4334 total hip replacements

John Annan, Nick Clement, Gavin J. Macpherson, Ivan J. Brenkel, James A. Ballantyne, Edward Dunstan

The aim of this study was to identify pre-operative and intra-operative factors that are predictive of dislocation following primary total hip replacement (THR). Data were prospectively collected for a consecutive series of 4334 THRs undertaken over a 14-year period. Ninety-eight (2.3%) of the 4334 patients had one or more dislocation post-operatively. A body mass index (BMI) of ≥ 35 (p < 0.001), a Harris Hip Score (HHS) of ≤ 41 (p < 0.001) and a low-volume surgeon (p < 0.001), which was defined as performing fewer than 43 THRs per annum, were identified as independent predictors of dislocation using logistic regression analysis. Using these three variables in differing combinations the risk of dislocation varied from 0.5 to 10.4%. Patients at high risk of dislocation, with a BMI of ≥ 35 and a pre-operative HHS of ≤ 41, undergoing surgery by a low-volume surgeon had a dislocation rate of 10.5%, but this decreased to 2.3% when operated on by a high-volume surgeon. These risk factors could be used to identify patients at high risk of dislocation, and modification of these factors, such as weight loss to achieve a BMI of ≤ 35 or referral to a high-volume surgeon, may decrease the risk of dislocation and the resulting secondary morbidity.