Efficacy of an AFCN Proxy Block in Post-TKA Multimodal Pain Management

Efficacy Assessment of Supra-Sartorial Subcutaneous Infiltration (SSSI) as an Anterior Femoral Cutaneous Nerve Proxy Block in the Multimodal Pain Management After Total Knee Arthroplasty: A Randomized Controlled Trial

This randomized controlled trial evaluates the additive effect of Supra-Sartorial Subcutaneous Infiltration (SSSI) when performed in combination with intermittent adductor canal block (iACB) and posterior capsule local infiltration analgesia (PC-LIA) for pain management after total knee arthroplasty (TKA). SSSI, an easy-to-perform tentative proxy block to targeted anterior femoral cutaneous nerve (AFCN) block, is tested in 90 adults (45-90 years) randomized into two arms: active SSSI versus sham SSSI. Primary outcome is pain scores at rest and during movement on postoperative day 0; secondary outcomes include daily pain trajectory at rest and during movement, functional recovery scores, rescue analgesic doses over days 0-3, and quality of recovery assessment on day 4.

This prospective, double-blinded, sham-controlled randomized controlled trial investigates the additive analgesic effect of Supra-Sartorial Subcutaneous Infiltration (SSSI) when combined with intermittent adductor canal block (iACB) and posterior capsule local infiltration analgesia (PC-LIA) following total knee arthroplasty (TKA). The SSSI technique was developed as a simplified, practical alternative to the technically demanding targeted anterior femoral cutaneous nerve (AFCN) block. Drawing on preliminary data where SSSI provided clinically meaningful analgesia in approximately 58% of patients when paired with PC-LIA, this trial evaluates the role of SSSI in enhancing motor-sparing analgesia within a multimodal framework. The study will enroll 90 adults between the ages of 45 and 90 undergoing unilateral primary TKA. Participants will be randomized 1:1 into two groups of 45, with stratification based on gender and baseline Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. All active interventions utilize 0.3% ropivacaine, while the control arm utilizes saline shams for the SSSI component. The SSSI and iACB catheterizations are performed by anesthesiologists in the post-anesthesia care unit, whereas the PC-LIA is administered intraoperatively by the surgical team. Patients in the active group receive active SSSI, active iACB, and active PC-LIA, while those in the sham group receive a saline SSSI alongside active iACB and active PC-LIA. The primary outcome is defined as Visual Analog Scale (VAS) pain scores at rest and during movement at 9:00 PM on postoperative day 0. Secondary outcomes include daily VAS pain scores at rest and during functional assessments such as continuous passive motion (CPM) and the timed up-and-go (TUG) test through postoperative day 1-4. Additionally, the trial monitors the maximal allowable degree of CPM, TUG test performance, cumulative rescue analgesic doses over the first 4 postoperative days, and Quality of Recovery-15 (QoR-15) scores on postoperative day 4. With approximately 96% power to detect a 2-point difference in pain scores, the trial aims to determine if SSSI significantly improves postoperative analgesia without compromising motor function.

Inclusion Criteria:

• Adults aged 45-90 undergoing unilateral primary TKA for osteoarthritis.
• American Society of Anesthesiologists (ASA) physical status I-III.
• Able to provide informed consent and use NRS pain scales.
• Surgery scheduled to start before noon to standardize spinal anesthesia recovery.

Exclusion Criteria:

• Bilateral or revision TKA.
• Contraindications to regional anesthesia (e.g., coagulopathy, infection at injection site).
• Chronic opioid use (>30 mg morphine equivalents/day) or preoperative NRS >4.
• Pre-existing neurological deficits in lower extremities or AFCN-related neuropathy.
• Allergy to ropivacaine.
• Pregnancy, breastfeeding, or cognitive impairment affecting assessments.