Building on Bayesian design methodologies from volume optimization studies of ropivacaine in shoulder surgery, this study pioneers the application of a seamless dose-finding strategy in knee ACB. Utilizing advanced statistical models (BOIN/BOP2 design), we aim to systematically evaluate the volume-effect relationship of liposomal bupivacaine, providing precise dosing recommendations to advance personalized and optimized analgesic protocols for knee surgery.
Patients undergoing elective general anesthesia for unilateral knee joint surgery.
Patients who provide informed consent.
Aged between 18 and 65 years old, regardless of gender.
American Society of Anesthesiologists (ASA) physical status classification of Ⅰ to Ⅲ
Femoral neuropathy.
Coagulation dysfunction.
Allergy to local anesthetics.
Infection at the puncture site.
Single group
Perform adductor canal block with liposomal bupivacaine.
DrugPatient Positioning: Supine with the surgical limb slightly flexed and externally rotated. Operator Setup: The operator stands on the surgical side, with the ultrasound machine positioned contralaterally. The anterior thigh is sterilized and draped. Ultrasound Technique: A high-frequency (5-12 MHz) linear ultrasound probe (Sonosite M-Turbo), protected by a 3M Tegaderm dressing, is placed perpendicular to the skin at the midpoint between the femoral trochanter and the superior patellar margin. The probe is maneuvered to visualize the adductor canal structures. Needle Insertion: After local anesthesia at the insertion site, a 22G 80 mm needle is advanced using an in-plane technique until the tip reaches the triangular hypoechoic area lateral to the femoral artery. Following negative aspiration for blood, 1.33% liposomal bupivacaine is injected around the target site.
The incidence rate of the decline in the motor function of the quadriceps femoris muscle
The maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle is measured using a handheld dynamometer (HHD) and then re - measured 30 minutes after the block. A decrease in muscle strength of ≥ 25% is defined as a significant impact on motor function.
The success rate of the block
Sensory block at 30 minutes after surgery (pinprick test at several sites in the area innervated by the saphenous nerve) and a resting NRS score ≤ 3 points. The sensory block is evaluated using a pinprick test for sensation. This test is performed before the adductor canal block (baseline) and every 5 minutes after the nerve block until 30 minutes have elapsed or the surgery begins. The sensory test is carried out in the distribution area of the saphenous nerve (medial side of the lower leg), as well as on the anterior, medial, lateral, and posteromedial sides of the surgical knee joint, and above the patella. A sensory score of 2 indicates normal sensation, 1 indicates hypoesthesia, and 0 indicates no sensation. We define a successful adductor canal block as the occurrence of sensory block in the surgical knee joint within 30 minutes after the nerve block, that is, the loss of sensation to the pinprick (sensory score of 1 or lower).
Numerical Rating Scale scores during resting/movement
The NRS (Numeric Rating Scale) scores range from 0 to 10 in total. A score of 0 represents no pain, while a score of 10 indicates severe pain. A score of 0 to 3 indicates mild pain, which is tolerable and does not affect sleep. A score of 4 to 6 indicates moderate pain, which is more obvious and will somewhat interfere with the patient's daily life and sleep, but is still bearable. A score of 7 to 10 indicates severe pain, which is intense and difficult to endure, seriously affecting the patient's daily life and sleep. The lower the score, the better the analgesic effect of the adductor canal block performed with liposomal bupivacaine.
Consumption of opioid drugs
converted into morphine equivalent, mg. After performing the adductor canal block with liposomal bupivacaine, the lower the consumption of opioid drugs, the better the effect of nerve block and the more prolonged the blocking duration.
Duration of analgesia
The time from the completion of the block to the first need for rescue analgesia.
The time of the first out-of-bed activity
Observe the impact of adductor canal block on the patient's motor function. If the patient can get out of bed and move for the first time within a relatively short and reasonable period, it usually indicates that the nerve block has a good effect. It can effectively relieve pain without excessively affecting the patient's motor function, enabling the patient to regain a certain degree of activity ability at an earlier stage.
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