This study employs a randomized controlled trial to investigate whether bupivacaine liposome injection for adductor canal block can effectively improve lower limb muscle strength after total knee arthroplasty.

Total knee arthroplasty (TKA) involves significant trauma, and postoperative patients often experience moderate to severe pain, which limits early knee joint functional exercise and affects functional recovery. Peripheral nerve blocks can effectively relieve pain, but while providing adequate analgesia, they may also affect the motor nerves of the lower limbs, increasing the risk of falls when patients begin ambulation. Some studies have found that the incidence of falls in patients using nerve blocks during the early postoperative period, especially during hospitalization, can be as high as 2% . The actual incidence in clinical practice may be even higher. The period of highest risk is when the nerve block effect has not completely subsided and patients begin attempting to ambulate, typically within 24 to 48 hours after surgery. The loss of muscle strength caused by motor nerve blockade is the most direct cause of postoperative falls, primarily due to severe weakness in key stabilizing muscle groups such as the quadriceps.The adductor canal block has clear advantages. However, traditional local anesthetics, represented by ropivacaine or bupivacaine, typically provide effective analgesia for only 12-24 hours after a single injection, making it difficult to fully cover the peak pain period of 48-72 hours postoperatively. Continuous femoral nerve block with ropivacaine can provide prolonged analgesia. When combined with a sciatic nerve block, it can achieve nearly complete analgesia coverage for the knee. Its drawback is its association with quadriceps impairment, which may increase the risk of falls. Continuous adductor canal block also provides prolonged analgesia and has a lesser impact on postoperative muscle strength, but it faces challenges such as catheter placement difficulty and inconvenience for postoperative mobility. In contrast, bupivacaine liposome can provide analgesia for up to 72 hours. If, while offering high-quality analgesia, bupivacaine liposome indeed causes significant weakening of quadriceps strength during the critical first 2-3 days after surgery, the safety and effectiveness of early patient ambulation would be greatly compromised, potentially even increasing the risk of falls. This would contradict the original intent of using the adductor canal block to preserve muscle strength. Conversely, if it is proven to have a lesser impact on muscle strength compared to continuous femoral nerve block, it could become an almost ideal analgesic option.

Inclusion Criteria:

1. Patients aged 60-75 years scheduled for elective TKA;
2. ASA physical status classification II-III;
3. BMI 18-30 kg/m²;
4. Agreement to participate in this study and provision of signed informed consent.

Exclusion Criteria:

1. Individuals with communication barriers such as language or hearing impairments;
2. Patients with contraindications to nerve blocks;
3. Severe systemic diseases, such as severe renal disease (estimated glomerular filtration rate below 50 mL/min), cardiac disease (congestive heart failure New York Heart Association Class III to IV), or severe hepatic disease defined as a current or past diagnosis of acute/subacute hepatic necrosis, acute liver failure, chronic liver disease, liver abscess, hepatic coma, or hepatorenal syndrome;
4. History of long-term opioid use (defined as daily or nearly daily opioid use within the past 3 months).