Summary

To our knowledge, this is the first randomized clinical trial to compare pain control and quadriceps function between patients receiving adductor canal (ACB) or femoral nerve blockade (FNB) with ACL reconstruction. Our results indicate that quad muscle activation and ambulatory rates are higher in patients receiving ACB. This information may help to reduce post-op complications in this population.

Abstract

Purpose/Hypothesis: Post-operative pain control is critical to successful outcomes following anterior cruciate ligament reconstruction (ACLR) in an outpatient setting. Femoral nerve blockade (FNB) has traditionally been employed to provide analgesia for ACLR since its inception in the early 1990’s. Unfortunately, several studies show a significant reduction in quadriceps muscle strength, and increased fall risk with the use of FNB. To mitigate the loss in muscle function and patient safety, surgeons and anesthesiologists have been exploring the potential benefits of the motor sparing adductor canal nerve blockade (ACB). To date, however, few comparative outcomes studies exist within an ACLR population. Thus, the purpose of this study was to compare acute pain control, quadriceps muscle activation and limb function between FNB and ACB in patients undergoing ACLR.

Study Design: Double-Blinded Randomized Clinical Trial

Number of Subjects: 83 (ACB=42, FNB=41)

Materials/Methods: Patients undergoing ACLR were randomly allocated prior to surgery to receive FNB or ACB. Pain control was assessed over the first 24 hrs of surgery using the numeric pain rating scale (NPRS) and opioid use in morphine units (mg). Quadriceps activation was measured using surface electromyography (EMG) and recorded as deficits between the involved and uninvolved limbs. Quadriceps muscle function was assessed via the number of successful straight leg raises performed (without a lag), and the ability to ambulate without an assistive device at 24 hrs, 2 weeks, and 4 weeks. A mixed-model ANOVA (time x group) was used for all statistical comparisons with an a priori a =.05.

Results

Patient demographics were similar at baseline for age (28.3 ±11.1 vs 26.7 ±10.0; P =.68), gender (61.9% male vs % 65.9 male; P =.17), and BMI (26 ±6 vs 27 ±8; P =.79) in the ACB and FNB groups, respectively. No differences were observed in NPRS scores (2.4 ±1.7 vs 2.6 ±2.0; P =.52), and Morphine units (24.1 ±16.3 vs 22.8 ±15.6; P =.61) for ACB and FNB groups. Quadriceps deficits were lower for the ACB group at each testing timeframe; 24-hours (202.2 ±36.3 vs 268.1 ±43.2; P =.04), 2-weeks (107.4 ±28.4 vs 158.4 ±37.2; P<.01), and 4-weeks (82.3 ±48.3 vs 123.8 ±51.9; P =.02). Functionally, a higher percentage patients receiving ACB were ambulatory at the 4-week assessment (P <.01). No statistical differences were observed for the number of straight leg raises performed at any of the testing timeframes (P >.05).

Conclusions

Our results indicate that ACB provides similar acute pain control with improved quadriceps muscle activation compared to FNB following ACLR. Additionally, the rate of full ambulation was higher those patients receiving ACB, although no influence was observed for the ability to perform a straight leg raise when compared to FNB.

Clinical Relevance: ACB may provide superior preservation of quadriceps muscle activation and the ability to ambulate with similar pain control when compared to the FNB following ACLR. Further study is needed to determine the potential long-term effects of nerve blockade on muscle strength and patient function at return to activity.