Blood flow restriction interventions before and after anterior cruciate ligament reconstruction: A systematic review

by Emma Shirley, SPT

Background

My first encounter with blood flow restriction (BFR) was an informal brush during my undergraduate years at East Carolina University. While working out at my local CrossFit gym, a guy next to me on the squat racks whipped out two thick elastic bands. He wrapped them extremely tightly around his proximal thighs, then proceeded to un-rack his weight and squat. An exercise physiology student at the time, I was perplexed. I asked him about it, and he told me about blood flow occlusion, which he claimed helped maximize “gains.” As a CrossFit coach and athlete, and a dabbler in the power and Olympic weightlifting sports, I have seen BFR implemented in many different forms, from elastic bands haphazardly wrapped around an exercising limb in a sweaty weight room, to a more nuanced and measured application in the clinic.

While the APTA endorses BFR training as part of physical therapy’s professional scope, is not taught formally in NC physical therapy school curriculum.^1,2 However, through independent reading of research publications, and exploring the physical therapy and sports medicine social media community, I learned independently about BFR. True, medical applications of BFR, unlike my friend at the CrossFit gym, use formal tourniquet devices to occlude venous return while decreasing arterial flow.² I found it very interesting not only because of its prevalence in my hobbies and sports, but also due to its rising popularity in many facets of physical therapy, from orthopedics and sports, to geriatrics and pelvic floor.^2-4 It seemed like something useful to pursue a certification in, as an aspiring orthopedics physical therapist.

My favorite unit in our musculoskeletal courses was the knee, but particularly ACL reconstruction rehabilitation; in class, we learned that ACL reconstruction rehabilitation is widely varied and there is a lot of controversy over the most appropriate protocol or approach. I had seen BFR discussed with ACL reconstruction rehabilitation on popular physical therapy social media accounts. I noticed a large body of research asserting that BFR creates positive clinical outcomes in patients at risk for sarcopenia.²¹ It seemed like a very interesting to question to pursue the efficacy of BFR, if any, in rehabilitation following ACL reconstruction.

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Statement of Need/Purpose

Anterior cruciate ligament (ACL) rupture is a common occurrence in both recreational and professional athletes.^7-10,12-16 It is estimated that approximately 200,000 ACL reconstruction surgeries are performed annually in the United States.⁹ Despite ACL reconstruction and current best practice rehabilitation, only 60% of amateur and 83% percent of elite athletes return to sport.^{7,13,15,16,23} Furthermore, of those whom return to sport, there is a prominent persistence of quadriceps strength deficits and limb strength asymmetry that results in decreased sports performance compared to before injury.^{7-10,12,14-16} These strength and participation impairments may persist for as long as 20 years following ACL reconstruction.⁹ Quadriceps strength deficits and limb strength asymmetry after ACL reconstruction has been linked to long-term consequences, such as early-onset knee osteoarthritis, despite prioritization of quadriceps strength during rehabilitation.^{9,12,13,14-16,23}

Strength training is typically implemented in post-ACL reconstruction rehabilitation by progressive overload using at least 70% of an individual’s 1-repetition maximum in order to trigger physiological strengthening responses.^5,6,18,21 Greater magnitudes of loading require a greater number of motor units, thus maximizing strength adaptations via higher rates of motor unit recruitment.⁶ However, this magnitude of heavy loading is not practical or safe during early rehabilitation after ACL reconstruction due to high mechanical stressors placed on healing tissues.^5,18 This combination of factors has created a need for safe but effective methods of muscular strengthening after ACL reconstruction.

Blood flow restriction (BFR) training is an alternate strengthening approach to the progressive overload principle and may be appropriate during early recovery. BFR involves the application of an inflatable cuff, wrap, band, or tourniquet during therapeutic activity or exercise, in order to occlude venous return from an active muscle while still allowing arterial blood flow.^5,11 BFR training has been shown to positively affect muscle strength and hypertrophy with lower amounts of external loading, and has been successfully applied in sports training and musculoskeletal rehabilitation, the latter particularly with older adults.^{5,11,17,18,20-22}  BFR interventions with older adults, paired with lower loading, have resulted in strength gains comparable to those elicited with heavy loading.^5,21 It is, however, unclear if BFR is any more effective in eliciting changes in strength than usual care following ACL reconstruction. BFR interventions may be appropriate for use before, or after, ACL reconstruction for application of stimulus mimicking heavy loading in rehabilitation while maintaining post-surgical precautions to avoid excessive stress on healing tissues. However, at the time of this writing, there have been no published systematic reviews examining the efficacy of BFR intervention with ACL reconstruction rehabilitation.

The purpose of this systematic review was to examine the effects of BFR intervention before or after ACL reconstruction on strength, pain, range of motion (ROM), and function. Pain, ROM, and function will be addressed in addition to strength due to their intricate relationship with patient rehabilitation participation and overall outcomes.

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Overview

The systematic review was performed on February 5, 2020 in CINAHL, Embase, PEDRo, ProQuest Health Administration Database, PubMed, Scopus, SportDiscus, and Web of Science. Three hundred and eleven studies were included for screening; eleven articles were included for final review. Two articles addressed the same study and cohort, so a total of 10 distinct studies were included. The average PEDro score for randomized studies was 5/10, indicating a moderate risk of bias. Eight studies included measures of strength, two included measures of pain, two addressed range of motion, and three involved self-reported or performance measures of function. There were inconsistent results all of the aforementioned examined outcomes. At this time, it cannot be said that BFR intervention yields superior results to usual care on strength, pain, ROM, and functional outcomes following ACL reconstruction. This is consistent for BFR intervention before surgery, and during early, middle, and late recovery after ACL reconstruction. This review had a number of limitations, including included studies’ risk of bias, differing post-operative rehabilitation protocols, variation in equipment and parameters of the BFR interventions, differing comparison groups, and lack of reporting of raw data. A greater number of higher-quality studies is needed to draw definitive conclusions on the application of BFR intervention before or after ACL reconstruction.

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Products

I conducted a systematic review on February 5, 2020 and created my primary product, a manuscript based on my findings intended for physical therapists and health care professionals. I created two layman-targeted deliverables- a layman’s summary and an infographic.

• Blood flow restriction interventions before and after anterior cruciate ligament reconstruction: A systematic review
• Layman’s summary
• Layman’s infographic

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Evaluation

The manuscript went through multiple peer and advisor reviews prior to finalization. These included after the writing of the introduction, methods and results, and the full draft. At each stage, a peer (Tanner Holden, SPT or Gabe Dimock, SPT) and Dr. Thoma performed independent reviews. Dr. Thoma also provided feedback for the infographic and layman’s summary prior to finalization. At midterm, committee members Dr. Jon Hacke and Dr. Jibran Qayumi were provided the introduction, methods, and results section with opportunities to provide feedback at needed. At final, they provided feedback on the final full manuscript as well as the layman’s summary and infographic.

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Self-Reflection

This has been a long process spanning over the length of two semesters. I have learned about the intricate process that goes into the conduction of a systematic review; it is much more involved than I initially thought. Additionally, I have learned how to look more closely at research, including weighing factors like comparison groups, risk of bias, and clarity of data reporting. This project has provided me with the tools to more confidently appraise and draw conclusions from research, even in new and emerging topics in which studies may be scarce. At the beginning of physical therapy school, I could not have imagined being able to accomplish a project of this scope. It was exciting to compile my knowledge over the past 3 years to produce a product that I find interesting and take pride in.

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Acknowledgments

First and foremost, my rockstar advisor, Dr. Louise Thoma, deserves endless praise. I worked with her for the past academic year, both during this capstone elective and the research credit I did with her in the spring. Conducting a systematic review is no walk in the park, but she patiently helped and enabled me to confidently complete this project and create a product I am proud of.

Secondly, I owe a big thank-you to my systematic review teammates and classmates, Tanner Holden and Gabe Dimock. I could not have gotten through endless hours of title and abstract screening full text review without you guys. Their reviews and feedback throughout the process were invaluable.

Thirdly, thank you my committee members, Dr. Jon Hacke and Dr. Jibran Qayumi, for providing desperately needed input and feedback. I especially appreciate that you took time out of your busy days during such a difficult time. Your expert opinions were key to perfecting this project.

Thank you to my mom Wendy, grandma Marilyn, and my dog, Kaylee, for the love and support throughout these three years of physical therapy school. I would not have been able to even have a chance to go to graduate school without you guys by my side. I am endlessly appreciative.

Finally, thank you to my classmates! I’m so grateful to have had such a great group to grow and learn with. I am excited to see where each of goes and the things we achieve during our careers.

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References:

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24. Blood flow restriction (BFR) therapy application. (A) Delfi Personalized Tourniquet System for BFR with pneumatic cuff (third-generation tourniquet). (B) Application of BFR during quadriceps activation exercise after arthroscopic knee surgery. In: DePhillipo NN, Kennedy MI, Aman ZS, et al. Blood flow restriction therapy after knee surgery: indications, safety considerations, and postoperative protocol. Arthroscopy Techniques. Oct 2018;; 7(10):e1037-43. DOI: doi.org/10.1016/j.eats.2018.06.010.