OBJECTIVE: Compare the effect of posterior surgical approach (PA) vs direct anterior approach (DAA) on speed of recovery from pain and dysfunction and on intrathecal oxytocin analgesia after total hip arthroplasty (THA). STUDY DESIGN: Nested cohort within a randomized, controlled, double-blind trial. SETTING: Hospital. SUBJECTS: Individuals aged 31 to 80 years undergoing total hip arthroplasty (THA). METHODS: In this secondary analysis of a randomized controlled trial, the association between surgical approach and number of daily steps was assessed, and whether this was modified by receipt of intrathecal oxytocin. Data were collected from accelerometers and daily patient diaries in the first eight weeks postoperatively. Outcomes were analyzed using generalized linear regression models. RESULTS: Ninety patients underwent THA, of which 35 (38.9%) received a PA. Patients were predominantly female (57.8%) with a mean age of 60.6 (standard deviation [SD] 9.3) years. On postoperative day one patients who received a PA with placebo took more steps (mean difference [MD] 53.72, 95% CI: -1717.86, 1825.31) than patients who underwent a DAA. Trajectories were significantly modified by whether they received oxytocin, in which patients who underwent PA with oxytocin took more steps than patients who underwent DAA (p<
0.001). DISCUSSION: Further studies are needed to understand mechanisms underlying oxytocin's interaction with surgical approach and guide considerations for recovery after THA.