Abstract

Background: Total hip arthroplasty (THA) is an effective treatment for advanced hip osteoarthritis, yet the influence of the surgical approach on early biomechanical and neuromuscular recovery remains debated. The direct anterior approach (DAA) is considered muscle-sparing, whereas the lateral approach (LA) involves partial abductor detachment and may influence postoperative gait and muscle activation. As a first step, this pilot study was designed primarily to assess the feasibility of an integrated, multidomain assessment protocol to combine clinical and patient-reported outcomes, instrumented gait analysis, hip biomechanics, and surface electromyography (sEMG), and to delineate preliminary trajectories of recovery after DAA versus LA THA to inform a future, adequately powered trial. Methods: In this prospective, non-randomized pilot study, 12 patients undergoing primary unilateral THA were evaluated and allocated according to surgical approach (DAA, n = 6; LA, n = 6). Assessments were performed at three months (T3M) and six months (T6M) postoperatively. Outcomes included pain intensity, SF-12, the Hip disability and Osteoarthritis Outcome Score (HOOS), instrumented gait analysis, hip kinematics and kinetics, and sEMG activity of the gluteus medius, semitendinosus, and rectus femoris of the operated limb. Given the small sample, between-group differences, within-group changes, and change scores from T3M to T6M were analyzed using non-parametric tests, and all results were treated as exploratory and hypothesis-generating. Results: Recruitment, retention, and completion of the full multidomain protocol were feasible, with no missing primary outcomes. Preliminary findings suggested that at three months, the DAA group showed lower pain and higher PCS-12, HOOS Total and HOOS Function scores, together with faster gait speed, longer normalized stride length, and shorter cycle and stance times. At six months, spatiotemporal gait parameters no longer appeared to differ between groups, suggesting the convergence of global gait performance, whereas the DAA group tended to maintain higher HOOS Total and Function scores and lower pain. The LA group showed greater late-stance hip extension and higher semitendinosus and rectus femoris sEMG amplitudes at T6M. Change-score analysis suggested a possible catch-up phenomenon in the LA group for gait speed, stride length, stance time, cycle time, and hip flexion range of motion, whereas semitendinosus activation tended to decrease in the DAA group and increase in the LA group. Given the limited sample, these observations are preliminary and require confirmation. Conclusions: This pilot study supports the feasibility of an integrated protocol combining patient-reported measures, instrumented gait analysis, and sEMG to characterize early recovery after THA. Preliminary, hypothesis-generating data suggest that DAA may be associated with a more favorable early postoperative clinical and spatiotemporal gait profile, with global gait performance tending to converge between approaches by six months, while persistent differences in hip-specific patient-reported outcomes and sEMG activation patterns hint that a similar gait performance may be achieved through different neuromuscular strategies. These preliminary findings should be interpreted with caution and used primarily to inform the design of larger, adequately powered studies with longer follow-up.

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