BACKGROUND: Quadriceps weakness is common after anterior cruciate ligament (ACL) injuries and ACL reconstruction (ACLR). Blood flow restriction (BFR) training is being increasingly used during ACLR rehabilitation protocols to facilitate a hypoxic cellular environment that triggers a local stress response theorized to promote muscle hypertrophy, and thus muscle strength, without mechanically loading a healing ACL graft. While BFR is a popular addition to therapy, scientific methods used to examine BFR training following ACLR have been inconsistent or insufficient to determine whether early BFR has a significant therapeutic effect on strength and function, and few studies have used advanced imaging to assess changes in muscle volume and composition. PURPOSE: This study aimed to investigate changes in postoperative quadriceps strength and muscle volume between conventional ACLR rehabilitation with early BFR training and conventional ACLR rehabilitation with sham (eg, non-therapeutic pressure) BFR training. We secondarily sought to evaluate the effect of early BFR training on late-stage functional and patient-reported outcomes (PROMs). METHODS: Ten individuals with a unilateral isolated ACLR were randomized to receive 200 minutes of BFR or sham (CON) training as part of their ACLR rehabilitation protocol. Quadriceps and hamstring strength were taken via a handheld dynamometer to calculate limb symmetry indices (LSI) at eight and 36 weeks postoperatively. Magnetic resonance (MR) images were acquired of the bilateral knees pre- and post-BFR or CON training and evaluated for muscle volume and adipose composition. Single-leg hop tests were performed at the conclusion of the rehabilitation protocol around 36 weeks postoperatively. PROM measures were measured by the International Knee Documentation Committee (IKDC) and Knee Injury and Osteoarthritis Outcome Score (KOOS) at baseline and eight and 36 weeks postoperatively. RESULTS: At eight weeks postoperatively, there was not a significant difference in quadriceps and hamstring LSI between the BFR and CON groups. At 36 weeks postoperatively, there was a significant increase in strength within all groups, but there were no significant differences in the improvement of either quadriceps or hamstring strength between the BFR and CON groups. There was no significant change in quadriceps intramuscular adipose composition or muscle volume between pre- and post-BFR MR images within the BFR group. There was additionally no difference between PROMs and adverse events between the two groups at the eight- and 36-week postoperative time points, and there were no complications with early BFR use. CONCLUSION: In this pilot study, quadriceps and hamstring strength, muscle volume, and intramuscular adipose were not impacted over time or between the BFR and standard-of-care groups. Early BFR utilization had no effect on PROMs between BFR and standard of care as measured by IKDC and KOOS. Larger studies are needed to better understand the potential effects of early BFR on patient rehabilitation after ACLR.

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