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Background and Aims Suprainguinal fascia iliaca block (SIFIB) provides effective analgesia for total hip arthroplasty (THA) but often causes quadriceps weakness. We hypothesized that low concentration local anesthetic (LCLA) SIFIB using 0.075% ropivacaine would offer comparable analgesia to high concentration local anesthetic (HCLA - 0.25% ropivacaine) while better preserving quadriceps strength.Methods In this double-blind randomized controlled trial, 43 patients undergoing primary THA received either LCLA-SIFIB or HCLA-SIFIB (50 mL ropivacaine + epinephrine 1:200,000) ( figure 1). All patients received standard spinal anesthesia (mepivacaine 2% 3.5 mL + fentanyl 15 mcg + morphine 100 mcg) and multimodal analgesia (standing Tylenol and celecoxib, hydromorphone PRN). Outcomes included pain scores (NRS), opioid consumption (oral morphine equivalents - OME), quadriceps strength (Oxford scale), and hospital length of stay.Results Groups were similar for baseline demographics ( table 1). Pain scores and opioid use were similar between groups at all time points (p > 0.26). Quadriceps strength at 8 hours after spinal anesthesia was significantly better in the LCLA group (median 4 [1–5]) vs. HCLA (median 2 [0–5], p = 0.0311). A trend favoring LCLA was also seen in PACU (p = 0.0544). Strength scores were comparable by POD1 and POD2 (table 2). No differences in adverse events were observed.Abstract OP52 Figure 1Image of supra inguinal fascia iliaca (SIFI) blockAbstract OP52 Table 1DemographicsAbstract OP52 Table 2Ostoperative outcomesConclusions LCLA-SIFIB provides comparable analgesia to HCLA-SIFIB after THA, with significantly improved early quadriceps strength. These findings support LCLA-SIFIB as a promising motor-sparing regional technique for enhanced recovery in THA patients.