The Delta of Correction: a novel, more reliable variable than limb-length discrepancy at predicting outcome after total hip arthroplasty

Background: Leg-length discrepancy (LLD) is a frequent and recurring issue after total hip arthroplasty (THA). It can lead to discomfort and litigation due to the patient's perception of this inequality. Purpose: The aim of this study was to evaluate the functional impact of postoperative LLD and length correction in patients after primary THA. We hypothesised that clinical outcomes are inversely correlated to length correction and residual discrepancy. Methods: In a prospective cohort, we included 121 patients undergoing unilateral primary THA. Patients were categorised into 3 groups based on their residual LLD using routine EOS imaging; Shorter (<-5 mm); Equal (-5 mm to +5 mm); and Longer (>+5 mm). Delta of Correction (DC) was defined as the difference between pre- and postoperative discrepancy measured on EOS imaging. Functional scores (HHS, Postel Merle d'Aubigne, and WOMAC) were measured preoperatively and at last follow-up. The average follow-up was 24 months. We evaluated the clinical and radiographic outcomes regarding the residual LLD and DC. Results: All patients had improvement in their functional scores at last follow-up. There was no difference in clinical outcomes, regardless of preoperative or residual LLD. The highest scores were found in the population with the smallest variations (DC -5 to +5 mm, HHS 96). Conversely, poorer results were found in shortened patients (DC <-5 mm), HHS 86, and lengthened patients, corrected by > 15 mm, with HHS of 83,p< 0.005. Patient perception of postoperative LLD correlated with the DC (p= 0.004). Conclusion: The DC measurement is a more effective assessment than arthroplasty.