The Impact of Injection Level on the Proximal Spread of Local Anesthetic and Clinical Outcomes in Adductor Canal Block

This prospective, randomized clinical trial is designed to evaluate the effects of two distinct injection levels of ultrasound-guided adductor canal block (ACB) on the proximal spread of local anesthetic and clinical outcomes in patients undergoing total knee arthroplasty (TKA). The study will be conducted at Ankara Etlik City Hospital with a total of 68 patients. All cases are limited to unilateral elective knee replacement surgeries performed under spinal anesthesia. Inclusion and Exclusion Criteria Inclusion criteria are defined as patients aged 18 years and older, with an ASA (American Society of Anesthesiologists) physical status of I-III, scheduled for elective unilateral TKA under spinal anesthesia. Exclusion criteria include patients scheduled for bilateral knee arthroplasty, known allergy to local anesthetics, chronic pain syndromes or regular opioid use, peripheral neuropathy or neurological diseases affecting femoral nerve function, coagulopathy or use of anticoagulant therapy, infection at the injection site, and patients unable to provide written informed consent. Randomization and Intervention Patients will be randomized into two groups using the sealed envelope method. In Group 1, the ACB will be performed under ultrasound (USG) guidance at the level where the vasto-adductor membrane (VAM) is first visualized. In Group 2, the block will be performed at the level where the adductor longus muscle ends. All blocks will be administered by experienced anesthesiologists using a standardized dose of 20 mL 0.25% bupivacaine. Clinicians performing the block will not be involved in the postoperative data collection process. Procedure and Monitoring All patients will undergo standard monitoring, including electrocardiography (EKG), non-invasive arterial blood pressure, and peripheral oxygen saturation (SpO_2). Following the administration of spinal anesthesia according to clinical protocols, the ACB will be performed under USG guidance based on the randomization results. Standard care will be provided throughout the surgical and anesthetic management, and perioperative data will be recorded. Outcome Measures and Evaluation Following the block, the spread of the local anesthetic will be evaluated in real-time using ultrasound. The distance between the injection point and the highest proximal point of the anesthetic spread will be measured in centimeters. Additionally, the spread area of the local anesthetic at the level of the apex of the iliopectineal fossa will be recorded using the planimetric measurement tools of the USG device. The reach of the local anesthetic to the femoral nerve will also be assessed via USG. Postoperatively, patients will follow standard clinical monitoring. Motor block will be evaluated based on the incidence of postoperative falls (yes/no). Sensory block efficacy will be assessed through total analgesic consumption recorded within the first 24 hours postoperatively. All collected data will be recorded for statistical analysis and compared based on the injection levels.