GENIVS Block Versus Adductor Canal Block After Total Knee Arthroplasty

Background: Total knee arthroplasty (TKA) causes severe postoperative pain that limits early physiotherapy and mobilization and prolongs hospital stay. Procedure-specific recommendations favor opioid-sparing multimodal analgesia that includes the adductor canal block (ACB), with opioids reserved for rescue. The ACB largely preserves quadriceps strength but does not cover the posterior knee capsule. The GENIVS (GENicular + iPACK + VastuS) block is a motor-sparing, ultrasound-guided periosteal plane block in which local anesthetic is deposited on the distal femoral periosteum and spreads circumferentially around the femur, aiming to block the genicular nerves, the nerve to vastus intermedius and the posterior capsular branches with a single injection. No randomized trial has compared the GENIVS block with the ACB.

Design: Single-center, prospective, randomized, double-blind, parallel-group non-inferiority trial at Bakirkoy Dr. Sadi Konuk Research and Training Hospital, Istanbul, Türkiye. The trial is registered before the first participant is enrolled.

Participants and randomization: Seventy-four patients aged 55-75 years (ASA physical status I-III) scheduled for elective, primary, unilateral TKA under spinal anesthesia will be randomized 1:1 to Group G (GENIVS block, n = 37) or Group A (ACB, n = 37). Before the study begins, a clinician outside the study team will generate the allocation list with Research Randomizer (www.randomizer.org) by drawing one set of 37 unique numbers from 1-74; these sequence numbers are allocated to Group G and the remaining 37 to Group A. The same clinician will prepare sequentially numbered, sealed, opaque envelopes. On the day of surgery, after eligibility is reconfirmed, envelopes are opened in sequence immediately before the block by an anesthesiologist who is involved neither in block performance nor in data collection, and the envelope number is recorded in the case report form.

Anesthesia and interventions: All patients receive standard monitoring, spinal anesthesia with 10-15 mg of 0.5% isobaric bupivacaine plus 10 µg fentanyl, and standardized sedation with intravenous midazolam 0.02 mg/kg. No periarticular or intra-articular local anesthetic infiltration is performed. At the end of surgery, while the patient is still under spinal anesthesia, an anesthesiologist with at least five years of regional anesthesia experience who is not involved in data collection performs the allocated ultrasound-guided block with 20 mL of 0.375% bupivacaine (75 mg). To maintain blinding, identical dressings are placed over both the GENIVS and the ACB needle-entry sites in every patient.

Postoperative analgesia: The time of PCA connection in the recovery unit is defined as hour 0. All patients receive intravenous tramadol PCA (4 mg/mL; 15 mg bolus; 20-minute lockout; no background infusion) for 72 hours, intravenous paracetamol 1 g every 6 hours (first dose at skin closure), rescue intravenous dexketoprofen 50 mg when the visual analog scale (VAS) score at rest is 4 or higher (at least 8 hours apart, maximum 150 mg/day), and intravenous ondansetron 4 mg for nausea or vomiting. No other analgesics or adjuvants are given.

Outcome assessment: All postoperative assessments are performed by investigators who are blinded to group allocation. VAS scores at rest and during active knee flexion are recorded at 2, 4, 8, 12 and 24 hours and, as exploratory outcomes, at 36, 48, 60 and 72 hours. Residual motor block from spinal anesthesia is assessed with the Bromage scale before each movement VAS. The Timed Up and Go test is performed at 24, 48 and 72 hours with a walker under physiotherapist supervision, stair climbing on postoperative day 2, the Turkish QoR-15 before surgery and at 24 hours, and the Opioid-Related Symptom Distress Scale at 24, 48 and 72 hours.

Sample size: Based on a reported mean 24-hour intravenous tramadol consumption of 262.9 ± 59.8 mg after ACB, assuming a common standard deviation of 80 mg, a non-inferiority margin of 65.7 mg (25% of the expected ACB consumption), a true difference of zero, one-sided α = 0.025 and 90% power, 33 evaluable patients per group are required. Thirty-seven patients per group (74 in total) will be enrolled to allow for 10% dropout.

Statistical analysis: The mean difference (GENIVS - ACB) in 24-hour opioid consumption is estimated with a two-sided 95% confidence interval; non-inferiority is concluded if the upper limit is below 65.7 mg in both the modified intention-to-treat and the per-protocol populations, and superiority is tested hierarchically thereafter. Secondary outcomes are compared with two-sided tests (Bonferroni correction for VAS time points, Kaplan-Meier and log-rank test for time to the first request, a linear mixed model with baseline as covariate for the Timed Up and Go test, and ANCOVA adjusted for baseline for QoR-15). Analyses are performed with IBM SPSS Statistics 32.0.