Injection Pressure & Adductor Canal Block

Unable to recruit additional patients due to transfer of surgical service (ortho sports medicine) and recruitable cases to another institution.

This is a prospective, randomized, single-blinded human clinical trial that will examine how injection pressure influences the spread of a given volume of injectate in the adductor canal, during adductor canal nerve block.

This is a prospective, randomized, single-blinded human clinical trial that will examine how injection pressure influences the spread of a given volume of injectate in the adductor canal, during adductor canal nerve block. The study population will be patients undergoing elective anterior cruciate ligament repair in the distal lower extremity and receiving preoperative adductor canal nerve blocks for postoperative analgesia. They will be randomized into two groups of 25 patients each. The investigators speculate that high injection pressures (>20 psi) will lead to greater spread of local anesthetic than low injection pressures (<15 psi) during mid-thigh adductor canal nerve blocks. The primary endpoint is the spread of injectate, defined as the distance between the uppermost and lowermost limits of spread of local anesthetic as assessed by ultrasound. The secondary endpoints are the incidence of femoral and sciatic nerve blocks 30 minutes after block placement, amount of IV opioid administered intraoperatively and postoperatively, preoperative and postoperative pain (Numeric Rating Scale, 0-10), and postoperative physical therapy milestone achievement.

Our primary endpoint is the spread of injectate, defined as the distance between the uppermost and lowermost limits of spread of local anesthetic as assessed by ultrasound.

Sensory testing will use a pinprick method in the femoral (anterior thigh), saphenous (medial calf proximal to the medial malleolus, top of the patella) and sciatic (posterolateral calf, plantar surface of the foot) nerve distributions; if patients are unable to feel the stimulus in the femoral nerve distribution, then an outcome of a femoral nerve block will be recorded.

Sensory testing will use a pinprick method in the femoral (anterior thigh), saphenous (medial calf proximal to the medial malleolus, top of the patella) and sciatic (posterolateral calf, plantar surface of the foot) nerve distributions; if patients are unable to feel the stimulus in the sciatic nerve distribution, then an outcome of a sciatic nerve block will be recorded.

Patients will rate their pain after surgery on a scale from 0-10, with 0 being no pain, and 10 being the worst pain of their life.

The patient will be evaluated by physical therapy postoperatively using the Lower Extremity Function Scale (LEFS). The LEFS is a self-reporting measure (0-80 score range, where 0 is complete disability and 80 is fully functional).

The patient will be evaluated by physical therapy postoperatively using the Lower Extremity Function Scale (LEFS). The LEFS is a self-reporting measure (0-80 score range, where 0 is complete disability and 80 is fully functional).

The patient will be evaluated by physical therapy postoperatively using the Lower Extremity Function Scale (LEFS). The LEFS is a self-reporting measure (0-80 score range, where 0 is complete disability and 80 is fully functional).

The patient will be evaluated by physical therapy postoperatively using the Lower Extremity Function Scale (LEFS). The LEFS is a self-reporting measure (0-80 score range, where 0 is complete disability and 80 is fully functional).

Intraoperative and immediate postoperative opioid administration. Calculated as morphine milliequivalent (in milligrams).

Inclusion criteria: Planned general anesthetic. American Society of Anesthesia classes I, II, or III. Patients aged 18-65. English-speaking patients. Exclusion criteria: ASA classes IV and V. Patients younger than 18 or older than 65. Contraindication to regional anesthesia (coagulopathy, patient refusal). Allergy to local anesthetic or other study medications. BMI > 35 kg/m2. Chronic opioid use (daily or almost daily use for > 3 months). Active illicit drug use. Additional surgical site other than the limb for adductor canal block. Pregnancy. Preexisting neuropathy in the operative limb. Inability to communicate to investigators or hospital staff. Inability to speak or understand English.