Injection Pressure & Adductor Canal 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.