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.

Inclusion criteria:

1. Planned general anesthetic.

2. American Society of Anesthesia classes I, II, or III.

3. Patients aged 18-65.

4. English-speaking patients.

Exclusion criteria:

1. ASA classes IV and V.

2. Patients younger than 18 or older than 65.

3. Contraindication to regional anesthesia (coagulopathy, patient refusal).

4. Allergy to local anesthetic or other study medications.

5. BMI > 35 kg/m2.

6. Chronic opioid use (daily or almost daily use for > 3 months).

7. Active illicit drug use.

8. Additional surgical site other than the limb for adductor canal block.

9. Pregnancy.

10. Preexisting neuropathy in the operative limb.

11. Inability to communicate to investigators or hospital staff.

12. Inability to speak or understand English.