The Efficacy of Blood Flow Restriction Training to Recover and Retain Quadriceps Strength and Function at a 6 Months Following an Anterior Cruciate Ligament Reconstruction. A Secondary Analysis of a Double-Blind, Randomized, Placebo Controlled Clinical Trial

Objectives: The use of blood flow restriction training (BFRT) has become increasingly popular after athletic injuries, such as an anterior cruciate ligament (ACL) reconstruction. In BFRT a cuff is applied to partially occlude arterial inflow and venous return in the injured limb while a person performs low-load exercises. Cuff inflation increases the metabolic demand of the quadriceps while limiting the absolute load across the reconstructed knee. By training under lower loads an individual may be able to train with less pain and experience similar benefits that occur with standard, higher load rehabilitation exercises. Between 4-6 months postoperatively an athlete typically transitions to more sport specific and higher load activities and discontinues supervised therapy such as low load exercises with BFRT. Whether or not the use of low-load BFRT during early rehabilitation leads to better recovery and retention of strength gains at 6 months than standard of care rehabilitation during the same period is unknown. To address this clinical gap, we performed a secondary analysis of a data from a completed clinical trial to determine whether the use of BFRT earlier in rehabilitation (first 4 months) resulted in better recovery and sustainment of quadriceps muscle strength, rate of torque development (RTD) and gait mechanics associated with the quadriceps (peak knee flexion angle and extensor moment) than standard of care rehabilitation at a 6 month follow up. We hypothesized that the use of BFRT would result in better recovery and retention (compared to baseline) of these performance outcomes than standard of care at a 6 month follow up. Methods: This is a secondary analysis of a double-blind, randomized, placebo controlled clinical trial that evaluated the effects of BFRT during early phases of rehabilitation on outcomes after ACL reconstruction. The study was prospectively registered on clinicaltrials.gov and had institutional review board approval. Forty-six athletes were randomly assigned to either low-load strength training with BFRT or standard of care training with sham BFRT. Participants performed BFRT (or sham BFRT) for one month pre-surgery and four months post-surgery. Both groups followed the same standard rehabilitation program and performed the same exercises (leg press, knee extension, squat, step up/down) 3x per week. Outcome variables were measured at baseline and 6 months post-surgery. Isometric quadriceps strength and rate of torque development were measured on an isokinetic dynamometer and normalized to body mass. An instrumented gait analysis was used to measure peak knee flexion angle and knee extensor moment. A Fisher’s exact test was used to assess between group differences in sex; two-sample t-tests were used to assess between group differences in age and each outcome (change from baseline to 6-months post-surgery). Results: There were no differences between groups for sex (X 2 =0, p=1.00, BFRT: 10F, 12M, Sham: 10F, 14M) and age (t 41.38 =0.42, p=0.68, BFRT: 20.9 ± 6.31 yrs, Sham: 21.58 ± 5.35 yrs). There were no significant differences between groups for change in quadriceps strength (t 42.08 =0.41, p=0.69, BFRT: 0.24 ± 0.7 Nm/kg, Sham: 0.32 ± 0.6 Nm/kg), RTD (t 34.12 =-0.02,p=0.98, BFRT: -0.06 ± 4.5 Nm/kg/s, Sham: -0.08 ± 2.7 Nm/kg/s) (Figure 1), peak knee flexion angle (t 35 =-0.32, p=0.75, BFRT: -4.43 ± 8.3 degrees, Sham: -5.1 ± 5.2 degrees) or peak knee extensor moment (t 41.27 =-1.1, p=0.28, BFRT: 0.054 ± 0.17 Nm/kg*m, Sham: 0.003 ± 0.143 Nm/kg*m) (Figure 2). Conclusions: One of the major purported benefits of using BFRT is that it will help athletes recover quicker than performing standard rehabilitation. Athletes in both groups ended up with a similar change from baseline in quadriceps muscle strength and gait mechanics at a 6 month follow up. These results suggest that athletes using BFRT do not recover and retain their strength any better than those receiving standard of care and are in no better position to pass return to sport testing. The use of a sham BFRT unit, rigorous blinding of the participants and assessors, and consistency in the physical therapist performing rehabilitation strengthened the study. Limitations of this study were that it was limited to one site, where the majority of patients received a bone patellar bone autograft, limiting generalizability to other graft types. In summary, these findings extend the field and question the use of BFRT to assist athletes in being able to recover and retain quadriceps strength and knee mechanics any better than standard of care rehabilitation.