True or apparent leg length discrepancy: which is a better predictor of short-term functional outcomes after total hip arthroplasty?

BACKGROUND AND PURPOSE: The associations between leg length discrepancy (LLD) and patient-perceived inequality and functional outcomes after total hip arthroplasty (THA) are unclear in the literature. The aim of this study was to determine the types of LLD after THA and to identify the best predictor of patient-perceived LLD and functional outcome in the short term after THA. METHODS: We subdivided LLD into true and apparent types and prospectively studied 53 consecutive patients undergoing unilateral primary THA to determine whether there is an association between the type of LLD and functional outcome 2 months after the operation. Apparent LLD was measured by the block test and true LLD was measured by hip radiography. We classified the patients into 4 groups: true, apparent, mixed, and no-LLD groups. The questionnaire included a visual analog scale of pain, the Western Ontario and McMaster Universities Osteoarthritis Index, and patient-perceived inequality. Physical performance was measured using walking speed and the Timed Up and Go test. RESULTS: The apparent and mixed LLD groups had a higher prevalence of patient-perceived inequality than the true and no-LLD groups. The results of physical performance showed that the walking speed of the mixed LLD group and the results of the Timed Up and Go Test of the apparent LLD group were significantly slower than those of the true LLD group. DISCUSSION: We suggested that the true LLD group may have a weak relationship with functional outcome after THA while the apparent LLD resulting from pelvic obliquity due to hip contracture or scoliosis is correlated with the short-term functional outcome after THA. CONCLUSION: Apparent LLD can be a better predictor of patient-perceived inequality and physical performance than true LLD.