PRE-OPERATIVE AND INTRA-OPERATIVE PREDICTORS OF TOTAL HIP ARTHROPLASTY DISLOCATION: A CONSECUTIVE, PROSPECTIVE SERIES OF 2899 PATIENTS

Abstract

Our aim was to identify intra-operative and post-operative factors that predict those patients most at risk of dislocation.

Data was prospectively collected on a consecutive series of 2899 total hip replacements undertaken between July 1997 and December 2007. All operations were undertaken in one institution by fourteen orthopaedic consultants. In order to ensure accuracy, our regional database was cross-referenced with the Scottish Arthroplasty Project. Age; sex; BMI; surgeon; surgical approach; monthly caseload per surgeon; and the head size of the implanted prosthesis were analyzed using chi-squared tests for categorised factors and t-tests for quantitative factors.

Of the 2899 patients, 78 (2.7%) were found to have had one or more dislocation. BMI > 35kg/m2 was a significant pre-operative predictor of dislocation (P< 0.001). BMI < 35kg/m2 had a dislocation rate of 2.3% compared with a rate of 6.7% in those > 35kg/m2. Operating surgeon was the only intra-operative factor predictive of dislocation (P< 0.001). Head size was found to be insignificant.

Three surgeons with an overall dislocation rate of < 1% had a dislocation rate of 0.8% for patients with a BMI < 35kg/m2 and 2.0% for BMI > 35kg/m2. In comparison, the remainder of the surgeons had rates of 3.3% for BMI < 35kg/m2 and 9.6% for BMI > 35kg/m2.

Analysis of this consecutive series has shown that a BMI > 35kg/m2 is associated with a significant increase in rates of dislocation. The operating surgeon is also a significant factor and the highest risk is seen in surgeons with a > 1% overall dislocation rate operating on obese patients.