Introduction: The Direct Anterior Approach (DAA) for hip replacement is an unfamiliar approach to most surgeons. The challenging portion of this approach is the preparation of the femur. In this study we determine factors that can assist in predicting the difficulty of femoral preparation to improve the learning curve.

Methods: Data was collected prospectively on 151 consecutive cases utilizing the DAA for hip replacement. After each case the femoral preparation was rated into one of 5 categories: very easy, easy, medium, difficult and very difficult. Clinical and demographic data were collected prospectively using web based data entry software. Post-operative x-rays were evaluated by an independent reviewer unaware of the exposure difficulty. Using multivariate regression, we examined several different x-ray based pelvic measurements as predictors for difficulty of femoral exposure.

Results: Univariate analysis demonstrated difficulty of femoral preparation was significantly (p< 0.05) correlated with height (OR=2.67, 95% CI = [1.03–6.94]), weight (OR=8.30, 95% CI=[2.35, 29.35]), male gender (OR=6.11, 95%CI=[1.97–18.97]), the distance from the greatertrochanter-to-ASIS (OR=0.30, 95%CI=[0.11–0.82]), teardrop-to-teardrop (OR=0.29, 95%CI=[0.11–0.79]), and greatertrochanter-to-greater-trochanter (OR=3.31, 95%CI=[1.23–8.95]). From this, we determined a simple pre-operative formula which allows the surgeon to predict difficult femoral preparations with an 87% sensitivity and easy preparations with > 95% specificity.

Conclusion: In MIS hip surgery, the DAA has proven difficult to learn for many surgeons. Careful patient selection can facilitate the learning curve and improve patient outcomes. We describe a simple to implement preoperative rating scale, which gives the surgeon learning DAA an algorithm for appropriate patient selection. With new advances in surgical procedures, selecting the appropriate patient can reduce the risks to the patient and minimize the cost to society of integrating new surgical techniques.