Objectives: Quadriceps weakness is common after anterior cruciate ligament (ACL) injuries and reconstruction (ACLR). Blood flow restriction (BFR) therapy is being increasingly used during ACLR rehabilitation to facilitate a hypoxic environment that triggers a local response for muscle strengthening and hypertrophy, while minimizing stress on the ACL graft. However, there are inconsistent or lacking data on the outcomes of BFR in this setting. The purpose of this study was to investigate changes in quadriceps muscle strength between conventional ACLR rehabilitation plus early (from 2-8 weeks postoperative) BFR therapy versus conventional ACLR rehabilitation with sham BFR therapy. We additionally sought to compare the effects of early BFR versus sham BFR therapy on late-stage functional performance, movement biomechanics, and patient-reported outcomes. Methods: Twenty-seven individuals with a unilateral isolated ACLR were randomized to receive 200-minutes of BFR or sham BFR (“CON”) training as part of their ACLR rehabilitation protocol from postoperative weeks 2 through 8. All physical therapy sessions were provided by 7 licensed physical therapists at an academic center (Figure 1). Primary measurements of quadriceps strength were taken via hand-held dynamometer by a blinded observer at 8- and at 36-weeks postoperatively, and limb symmetry indices (LSI) were calculated. Magnetic resonance images (MRI) were acquired of the bilateral knees preoperatively and after 8 weeks of BFR or CON training and evaluated for muscle volume and adipose composition. Single-leg hop testing LSI (6-meter, distance hop, and triple hop) and patient-reported outcomes (International Knee Documentation Committee and Knee Injury and Osteoarthritis Outcome Scores) were compared between groups at 36-weeks postoperatively. Using effect size from existing literature on the effect of BFR on quadriceps strength, we calculated that 12 participants were required in each group for adequate power. Results: At 8-weeks and 36- weeks postoperatively, there were no significant differences between BFR and CON groups for the primary outcome of quadriceps LSI (Table 1). Both groups significantly increased quadriceps and hamstring LSI over time. No significant differences in adipose composition or muscle volume were observed for the either group, in either limb, between pre- and 8 week postoperative MRI. There were additionally no differences between functional hop testing or patient-reported outcomes between the two groups at the 36-week postoperative timepoint. Conclusions: In this randomized controlled trial, addition of early (postoperative weeks 2-8) BFR to standard ACLR rehabilitation protocols resulted in no difference between groups for the primary outcome of quadriceps strength at 8- and 36-weeks postoperatively. Adipose composition, muscle volume, hamstring strength, functional testing, and patient-reported outcome measures were similar between groups at the tested time intervals.
Ohlsen et al. (Mon,) studied this question.