Blood Flow Restriction Training in the Adolescent Patient: Effects on Muscle Strength and Overall Function Following Anterior Cruciate Ligament Reconstruction Surgery

Background:

Approximately 100,000 anterior cruciate ligament reconstructions (ACLR) are performed yearly, and rates of these surgeries in patients younger than 15 years increased by 924% between 1990 and 2007.1 Persistent strength deficits in quadriceps musculature following ACLR are common, even several months after surgery and despite targeted physical therapy to address atrophy.2 Quadriceps atrophy and weakness are associated with worse patient-reported outcomes (PROs),3 as well as altered movement strategies and increased risk of reinjury.4,6 Approximately 20% of teenagers returning to sports will sustain a second ACL injury in the first two years following their ACLR.5 Regaining neuromuscular activation and strength of the quadriceps muscle safely and efficiently is vital to full recovery, and current post-operative physical therapy regimens have not sufficiently addressed this impairment.

Strength training models recommend utilizing high resistance workloads to produce substantial strength gains,7 yet those recovering from orthopedic surgery are unable to tolerate heavy loads.8 Supplementing low-load resistance training with blood flow restriction (BFR-LLT) produces significant muscle hypertrophy and strength gains previously only thought to be achievable with high-load resistance training.9 BFR-LLT uses a tourniquet around the leg (see Appendix 4) to partially occlude venous return and decrease blood supply to the muscle being exercised. The generation of a low-oxygen environment and increases in plasma growth hormone levels has been shown to promote recruitment of motor units, improve neuromuscular activation, and result in muscular hypertrophy and growth.10-13 In adults and the elderly, improvements in quadriceps strength have been reported in up to 19%14 and increased quadriceps cross-sectional area in up to 6-7% compared to controls.15-16 To date there have only been four high-level studies investigating effects of BFR training in patients following ACLR17-20 and limited conclusions can be drawn from these studies due to lack of consistent methodology (variable cuff pressures and treatment frequency). More high-quality research is needed to determine treatment parameters that produce the most optimal results from this intervention in ACLR patients.

Additionally, there are no published randomized controlled trials investigating the effects of BFR training on exclusively adolescent patients. All high-quality BFR training research in patients following knee surgery have been conducted in late adolescent, young adult and adult populations.17-21 Therefore, the purpose of this study is to assess the effect of BFR-LLT on quadriceps strength and outcomes in adolescents following ACLR.

This study's adolescent-specific focus provides a significant contribution to ACLR research, as younger patients demonstrate higher risk of reinjury.22-24 The results from this preliminary study will ultimately provide data to guide clinicians in optimizing quadriceps strength and utilizing BFR-LLT in younger post-operative ACLR patients.