We hypothesized that pericapsular nerve group (PENG) block was non-inferior to intrathecal (IT) morphine regarding analgesia after total hip arthroplasty (THA) with no untoward effects on the motor function.

In a double-blind placebo-controlled non-inferiority trial, patients undergoing unilateral THA under spinal anesthesia were randomized to receive a PENG block (20 mL 0.5 % levobupivacaine +2 mg dexamethasone) or IT morphine (100 μg). They received multimodal oral postoperative analgesia with rescue intravenous morphine for breakthrough pain, and were repeatedly evaluated for pain over the first 48 postoperative hours using a 0–10 numerical rating scale (NRS), and for the straight leg raise test at 4, 6 and 12 h. Co-primary outcomes were (i) maximum pain at rest and (ii) at active hip flexion – estimated for the overall period based on three consecutive scores – and (iii) milligram morphine equivalents (MME) delivered over 48 h. Non-inferiority margins for the PENG block – IT morphine differences were 0.75 NRS points for the pain scores, and 10 for the cumulative MME (corresponds to one 4 mg intravenous morphine rescue dose).

All randomized patients ( N  = 60, 1:1 ratio) completed all trial procedures. PENG block – IT morphine differences in the maximum pain at rest (difference = 0.182, 95 %CI -0.218 to 0.582) and at hip flexion (difference = −0.270, 95 %CI -0.990 to 0.453) were well below 0.75 NRS points, and the difference in MME (difference = −2.1, 95 %CI -6.5 to 1.9) was well below 10 MME. Age-adjusted straight leg raise test failure rates were similar in the two groups (11.7 % vs. 12.8 %, difference = −1.1, 95 %CI -9.7 to 7.5).

Compared to IT morphine, PENG block provides non-inferior analgesia after THA under spinal anesthesia without additional compromise of the motor function.

Trial registration number: NCT05308420