Total knee arthroplasty (TKA) causes intense postoperative pain that supports use of multimodal analgesia with long-acting regional techniques. Historically, femoral nerve block provided effective pain control but produced quadriceps motor blockade and delayed mobilisation. The adductor canal block (ACB) has become a preferred motor-sparing alternative because it primarily targets sensory branches while preserving quadriceps strength and facilitating early ambulation.
ACB alone does not cover all periarticular sensory inputs. The common clinical approach combines ACB with surgeon-delivered peri-articular local infiltration analgesia (LIA) using long-acting local anaesthetics, a strategy supported by PROSPECT recommendations and associated with reduced pain scores, lower opioid use and improved early range of motion. However, LIA and peripheral nerve blocks differ in anatomical distribution, operator dependence and timing, raising the question whether a predefined sensory-oriented multi-block strategy can substitute for active infiltration without loss of efficacy.
Recent studies suggest that adding targeted peripheral nerve blocks to ACB can enhance analgesia, but many comparisons are limited by inconsistent infiltration use or augmentation rather than substitution designs. The INCA trial addresses whether a motor-sparing four-nerve block strategy (ACB + lateral femoral cutaneous nerve + obturator nerve + IPACK) can replace active peri-articular infiltration while preserving early recovery and acceptable motor function.
The primary objective is to determine whether a four-nerve block strategy improves early postoperative global recovery compared with the standard multimodal strategy of single-shot ACB plus active surgeon-delivered ropivacaine LIA. Global recovery is measured by the Quality of Recovery-15 (QoR-15) score at 24 hours postoperatively.
Secondary objectives compare pain intensity at specified postoperative time points (2, 6, 12, 24 and 48 hours, and 1 month), total opioid consumption in the first 48 hours (expressed as intravenous morphine equivalents), adjunct analgesic and antiemetic use, need for rescue analgesia including rescue infiltration, motor function, adverse events, knee range of motion at 48 hours, time to first ambulation, PACU stay and total hospital length of stay, QoR-15 at 48 hours and change in KOOS-JR from baseline to 1 month. Safety outcomes include quadriceps or adductor weakness, falls and block-related complications.
INCA is a prospective, multicentre, parallel-group, randomised controlled superiority trial conducted in two French private hospitals: Hôpital Privé Claude Galien (Quincy-sous-Sénart) and Clinique des Côtes du Rhône (Roussillon). One hundred adult participants undergoing elective primary unilateral TKA for gonarthrosis will be randomised 1:1 (50 per arm). Recruitment is planned to start 30 April 2026 with estimated primary completion in January 2027 and study completion in February 2027.
Randomisation is computer-generated with concealed allocation through a secure web-based system or sequentially numbered opaque sealed envelopes. To preserve blinding, participant-facing sham procedures are used: control patients receive active ACB and active peri-articular LIA plus sham additional blocks, while intervention patients receive active ACB and active lateral femoral cutaneous, obturator and IPACK blocks plus sham surgical infiltration. Participants, ward staff, physiotherapists, postoperative outcome assessors, data managers and statisticians remain blinded. The anaesthesiologist performing regional blocks and the surgeon performing infiltration cannot be blinded.
Eligible adults are ≥18 years scheduled for elective unilateral primary TKA and able to provide written informed consent and comply with procedures. Key exclusions include prior major surgery on the index knee, neurological disorders affecting lower limbs, contraindications to regional anaesthesia (relevant anticoagulation, local infection, allergy), severe cognitive or psychiatric disorders, concurrent interventional trials interfering with outcomes, anatomical conditions preventing ultrasound-guided blocks, lack of French social security affiliation, legal protection status, pregnancy and women of childbearing potential without effective contraception per local rules.
All participants receive standardised general anaesthesia with predefined induction and maintenance agents and identical systemic multimodal analgesia (paracetamol, NSAIDs, nefopam and rescue opioids). An ultrasound-guided single-shot ACB with ropivacaine is performed in both groups.
Control group (standard strategy): active ACB plus surgeon-delivered peri-articular LIA with ropivacaine targeting posterior capsule and periarticular soft tissues, plus sham lateral femoral cutaneous, obturator and IPACK blocks.
Intervention group (four-nerve block strategy): active ACB plus active lateral femoral cutaneous nerve block, active obturator nerve block and active IPACK block performed with ropivacaine, together with sham surgical infiltration. This design tests substitution of infiltration by broader sensory block coverage.
Blocks are performed by anaesthesiologists experienced in ultrasound-guided lower-limb regional anaesthesia. For the protocol an experienced operator has independently performed at least 50 ACBs and at least 20 procedures for each adjunct technique, or has local documented sign-off after supervised training. Site initiation sessions will align procedures, sham techniques, anaesthetic doses and case-report completion. The same pool of operators will perform procedures in both arms when feasible; procedural variables and deviations are prospectively recorded.
Block failure is predefined as technical inability to complete the allocated procedure or absence of expected sensory effect within the assessment period. Inadequate analgesia is defined as postoperative pain ≥4/10 at rest or ≥6/10 during mobilisation despite standard multimodal analgesia. Rescue measures follow a predefined escalation algorithm and may include systemic analgesia escalation and, when clinically indicated, rescue active infiltration. Rescue infiltration is recorded as a protocol deviation and constitutes treatment contamination. Participants remain in their originally assigned groups for intention-to-treat analysis.
Primary outcome: QoR-15 score at 24 hours.
Secondary outcomes: pain intensity at 2, 6, 12, 24 and 48 hours and at 1 month; total opioid consumption in the first 48 hours (morphine equivalents); use of adjunct analgesics and antiemetics; frequency and timing of rescue infiltration; motor function and specific assessments for quadriceps and adductor weakness; adverse events; time to ambulation; knee range of motion at 48 hours; PACU and hospital length of stay; QoR-15 at 48 hours; and KOOS-JR change at 1 month. Safety endpoints are considered exploratory.
Randomised 1:1 allocation with concealed sequence generation and blinded outcome assessment are implemented to reduce bias. The protocol specifies intention-to-treat analysis. Secondary endpoints are exploratory. The registry entry and manuscript were harmonised for arm descriptions, outcome wording and assessment time points prior to resubmission.
The protocol was approved by the regional ethics committee (Comité de Protection des Personnes). All participants provide written informed consent. The trial adheres to the Declaration of Helsinki and Good Clinical Practice. Results will be shared with participants, submitted for peer-reviewed publication and presented at conferences. Trial registration: NCT06920186. Protocol version 4.0 is dated 11 February 2025.
Key strengths include concealed randomisation, participant-facing sham procedures with blinded postoperative assessments, standardised general anaesthesia and systemic multimodal analgesia across arms, and use of a validated primary endpoint (QoR-15 at 24 hours). Limitations noted by the investigators are operator-dependent block performance, inability to blind the procedural anaesthesiologist and infiltrating surgeon, and conduct in two private centres with experienced regional anaesthesia teams, which may restrict generalisability despite a pragmatic perioperative pathway.