Blood flow restriction training in rehabilitation for knee conditions and elective knee procedures

Abstract

Rehabilitation protocols for various knee conditions and elective procedures are essential for restoring function and patient satisfaction, as these conditions are frequently associated with significant muscle strength loss and may eventually require prolonged recovery. This minireview highlights the adjunctive role of blood flow restriction (BFR) training in this context. The fundamental principles of BFR involve controlled external occlusion to induce physiological training effects with substantially reduced mechanical load. BFR was added to various rehabilitation protocols for patients with knee conditions, such as primary osteoarthritis and rheumatoid arthritis, and was also applied during the rehabilitation of patients undergoing knee-related surgical interventions, including anterior cruciate ligament reconstruction and total knee arthroplasty. Various studies, systematic reviews, and meta-analyses have shown the effectiveness of BFR in improving muscle strength and function, with added value for functional outcomes and patient satisfaction. Furthermore, it showed an acceptable safety profile. However, a clear description of the protocols for BFR, tailored to each patient and procedure, should be provided. Moreover, long-term data on BFR involvement in the rehabilitation protocols for different knee conditions and after various surgical procedures, compared with conventional rehabilitation protocols, are still required.

Key Words: Blood flow restriction; Rehabilitation; Knee joint; Osteoarthritis; Total knee arthroplasty; Anterior cruciate ligament reconstruction

Core Tip: Rehabilitation is a crucial step in the conservative management of various knee conditions, including osteoarthritis and rheumatoid arthritis. Furthermore, it is a crucial step in the pre- and postoperative protocols for various elective knee joint surgical procedures, such as total knee arthroplasty and anterior cruciate ligament reconstruction. Blood flow restriction was introduced as an adjuvant to these rehabilitation protocols, demonstrating efficacy in improving muscle strength and performance, ultimately leading to improved function and quality-of-life outcomes. However, detailed descriptions and precise protocols for each condition supported by well-designed studies are still lacking.

INTRODUCTION

Among other well-documented rehabilitation procedures and techniques, blood flow restriction (BFR) therapy or training has emerged as a promising modality applied to various knee joint conditions, both pre- and postoperatively, with promising outcomes[1-5].

It was first introduced in Japan by Dr. Yoshiaki Sato, and it was known as ‘KAATSU Training’, meaning adding pressure to training[6]. Furthermore, its application evolved over the years, not only to improve muscle growth but also to enhance muscle endurance, reduce pain, increase bone density, and improve cardiovascular fitness[6-8].

BFR therapy involves using a tourniquet proximally on the working limb to compress vascular structures, restricting venous blood return and leading to metabolite accumulation in the working muscles. Moreover, occlusion of arterial flow will cause local hypoxia in working tissues, and these simple effects form the basis of the BFR therapy mechanism of action[9,10]. It should be noted that some adverse events have been reported owing to vascular occlusion, such as deep venous thrombosis and rhabdomyolysis; however, the overall safety profile of the procedure is high[11,12].

The current review aimed to shed light on the application and benefits of BFR therapy in the rehabilitation of knee joint conditions and elective surgical procedures, both pre- and postoperatively, and to provide insight into the results reported in recent literature.

HOW DOES BFR WORK?

It is essential to understand the mechanism of BFR-assisted rehabilitation before exploring its application in elective orthopedic procedures. Various mechanisms have been proposed to explain how BFR therapy works; however, in general, it relies primarily on metabolic stress induced by controlled vascular occlusion, which is further augmented by mechanical tension from resistance training, leading to muscle hypertrophy and increased strength[13,14]. The relative BFR-induced ischemia and hypoxia will increase metabolites produced by muscles, which are already known to accumulate during exercise and are responsible for muscular hypertrophy. Furthermore, the induced peripheral fatigue will increase motor unit recruitment, which explains how BFR under low loads had similar recruitment effects to high-load resistance training (HLRT)[15,16]. Interestingly, greater motor unit recruitment was observed in muscles proximal to the occlusion, not limited to the distal muscles[17,18]. It has also been shown that type II fast-twitch muscle fibers can be activated at lower loads under BFR conditions, whereas they are typically recruited at higher intensities[19]. Another mechanism that might explain the physiological benefits of BFR is satellite cell proliferation, which are multipotent cells responsible for muscle growth and regeneration[19,20]. Lastly, cell signaling pathways might be involved in the physiological adaptation observed with BFR application, including stimulation of protein translation through the mechanistic target of rapamycin (mTOR) pathway, which plays a role in muscle hypertrophy[2]. On the contrary, myostatin, a negative regulator of muscle growth, has been shown to decrease with BFR application[21].

Patient selection, precautions, and potential drawbacks of BFR

Although the results of BFR are encouraging, several issues should be considered before its widespread adoption, including patient selection, precautions, and potential drawbacks.

Patient selection criteria: BFR is ideally suited for patients and individuals who cannot handle heavy loads due to injury, surgery, or atrophy. It should be avoided in patients with a history of previous or active deep vein thrombosis, pregnant patients, those with severe uncontrolled hypertension, active limb infection, malignancy, and in patients with a history of vascular graft application or peripheral vascular disease. Furthermore, some authors consider patients with diabetes, cardiovascular disease (such as atrial fibrillation and arrhythmias), overweight, and a history of rhabdomyolysis as a relative contraindication for BFR[22-24].

Precautions and safety guidelines

To minimize the risk of developing adverse effects while implementing BFR, details of the different training protocols, preferred pressure, and the number of sessions are well described in the literature[12,25]. However, the following precautions should be considered[24].

Individualized pressure: Calibrated pneumatic cuffs should be used to determine limb occlusion pressure (LOP) and must be individualized for each patient rather than using arbitrary pressures.

Optimal pressure: Generally, 40%-80% of LOP should be used, with lower pressures for the upper limb and higher pressures for the lower limb.

Duration: Prolonged restriction should be avoided; typical sessions should involve 30 repetitions, followed by 3 sets of 15 repetitions with 30 seconds of rest, keeping the total occlusion time under 20 minutes.

Proper cuff placement: Place the cuff at the most proximal point of the limb (upper arm just under the deltoid; upper thigh near the gluteal fold). The area should be well-padded.

Monitor symptoms: Stop immediately if the patient feels dizziness, lightheadedness, numbness, or severe pain.

Generally speaking, current evidence supports pressures of 40%-80% LOP, a 30-15-15-15 repetition scheme with 30-second rests, and total occlusion times under 20 minutes per session. Furthermore, it is worth noting that using automated, calibrated pneumatic cuffs with Doppler-verified LOP is strongly preferred over manual or arbitrary pressure settings to minimize inter-operator variability and reduce the risk of neurovascular complications.

Possible drawbacks and risks

Although BFR-assisted rehabilitation protocols and exercises are generally considered safe for physically fit and healthy individuals, concerns have been raised about potential drawbacks when used in patients with musculoskeletal conditions[11,22]. Unfortunately, significant drawbacks might be associated with BFR, especially in patients with a history of cardiovascular conditions such as rhabdomyolysis, which could further lead to kidney injury, pain, numbness originating from excessive pressure causing nerve compression or damage, bruising, subcutaneous hemorrhage, and delayed onset muscular soreness[23,26,27].

How is BFR beneficial for the rehabilitation of various knee conditions and after elective surgical procedures related to the knee joint?

We performed a broad research on PubMed restricted to English language including articles published within the last 10 years, using combination of the following general search terms including using combinations of the terms “blood flow restriction”, “BFR”, “knee”, “osteoarthritis”, “rheumatoid arthritis”, “patellofemoral pain”, “anterior cruciate ligament reconstruction”, “ACL reconstruction”, “total knee arthroplasty”, “rehabilitation”, and “physical therapy” to identify the possible studies to include in the current minireview. Priority was given to systematic reviews, meta-analyses, randomized controlled trials (RCTs), and clinically relevant prospective studies in English, while studies not focused on knee conditions, nonclinical basic science articles unless needed for mechanism, and reports with insufficient rehabilitation or BFR protocol details were excluded. Although we tried to select the most relevant and better-designed studies, the search was not as structured or detailed as it would be for a systematic review. However, we believe that the selected articles will address the purpose of the current review. Based on the literature review, various implications of BFR therapy for the rehabilitation of orthopedic patients with different knee conditions were identified, both pre- and postoperatively.

Rehabilitation of patients with knee pain and degenerative knee conditions

Degenerative knee conditions, including primary osteoarthritis (OA), patellofemoral syndrome (PFS), or degeneration secondary to inflammatory arthropathy such as rheumatoid arthritis (RA) may lead to chronic pain and secondary muscle atrophy and weakness[28]. A possible conservative management line for these conditions is rehabilitation involving various types of exercise[29].

Primary knee OA: In a systematic review and meta-analysis ,Yang et al[5] included 14 RCTs involving 866 patients with knee OA were included. Compared with low intensity resistance training, including BFR in the rehabilitation protocol significantly reduced pain (MD: -1.72; 95%CI: 2.44 to -1.00), resulted in better functional outcomes (MD: 7.12; 95%CI: 2.21-12.02), and improved muscle strength (MD: 0.89; 95%CI: 0.18-1.20). Compared with high-intensity resistance training, BFR showed slightly better pain outcomes (MD: -0.43; 95%CI: -2.26-1.40) and strength (MD: 0.54; 95%CI: 0.39-1.48).

Knee RA: Rodrigues et al[30] conducted an RCT involving 48 females with RA to assess the effects of partial BFR combined with a low-load resistance training program. They reported that patients who had BFR with the low-load resistance training showed similar results to those who had HLRT regarding increasing maximum dynamic strength in both leg press (22.8% and 24.2%, respectively; P < 0.0001) and knee extension (19.7% and 23.8%, respectively; P < 0.0001). Furthermore, they found a significant increase in quadriceps muscle cross-sectional area, comparable across both modalities (9.5% and 10.8%, respectively; P < 0.0001). Functional outcomes, as measured by the timed-stands and timed-up-and-go tests, were also significantly improved with BFR compared with HLRT. Interestingly, the Health Assessment Questionnaire and quality of life (Short Form 36 health survey) measured at baseline and after intervention only improved in the BFR group. The authors concluded that adding BFR to low-load resistance training improves muscle mass, quality of life, and functional outcomes in RA patients.

PFS: Kong et al[31] conducted an RCT to evaluate the effect of introducing BFR in the management of patients with anterior knee pain or PFS. They included 42 patients divided into two groups (BFR vs control), in which the BFR group performed low-load resistance training under individualized LOP of 80%. In contrast, the control group performed HLRT. After 8 weeks, they reported that BFR resulted in significant improvement in pain (43.08% improvement, 95%CI: 33.59-52.58) and function (7.56% improvement, 95%CI: 3.50-11.62) compared with pre-intervention values. However, there was no difference compared with the control group. The authors noted that BFR application resulted in higher adherence and fewer adverse events [4 (19%) events in the control group vs 0 (0%) in the BFR group]. The authors concluded that for patients with anterior knee pain, adding BFR to low-load resistance training is a safer, tolerable approach, with outcomes comparable to those of high-intensity resistance training.

Combined knee OA and RA: Chen et al[4] conducted a systematic review and meta-analysis that included 12 RCTs, in which 642 patients with various knee diseases were evaluated (7 studies included knee OA patients, 4 included TKA patients, 1 included patients with RA). The authors found that BFR training did not improve pain scores compared with low-load control or high-intensity resistance training (standardized mean differences were -0.10 (P = 0.46) and 0.84 (P = 0.17), respectively. Furthermore, preoperative BFR training did not improve postoperative pain scores (SMD = 0.77, P = 0.37). However, BFR training significantly improved muscle strength compared with low-load control resistance training (SMD = 1.11, P < 0.00001). In a group of patients who had preoperative BFR training, postoperative muscle strength was significantly enhanced (SMD = 0.97, P = 0.03).

BFR for perioperative rehabilitation

Perioperative rehabilitation, including pre- and postoperative programs, is essential for better outcomes after operative knee procedures. BFR was highlighted for the rehabilitation of patients undergoing anterior cruciate ligament reconstruction (ACLR) and total knee arthroplasty (TKA)[4,32-34].

BFR in rehabilitation after ACLR

Patients who undergo ACLR are predisposed to postoperative muscle atrophy and weakness, and the main aim of rehabilitation protocols is to regain muscle strength and function as early as possible, where new rehabilitation strategies have been applied to enhance recovery[35-37].

Gopinatth et al[36] conducted a systematic review and meta-analysis of eight RCTs, in which 245 patients who underwent ACLR were included (130 of whom received BFR rehabilitation protocols for 8-12 weeks). Patients who had BFR rehabilitation showed significant improvement in isokinetic muscle strength (SMD = 0.77, P = 0.02, I²: 58%), better functional outcomes as measured using the International Knee Documentation Committee (IKDC) score (mean difference: 10.97, P ≤ 0.00001, I²: 77%), and less pain (SMD: 1.52, P = 0.04, I²: 87%). However, there was no difference in quadriceps muscle volume (SMD: 0.28, P = 0.43, I²: 76%).

Li et al[3] evaluated 11 studies including 276 ACLR patients in their systematic review, of whom 139 received BFR rehabilitation protocols. Their meta-analysis failed to show superior quadriceps strength with BFR compared with the control group (SMD = 0.82, 95%CI: -0.17-1.81, P = 0.10) early postoperatively. However, BFR rehabilitation resulted in significantly better functional outcomes per the IKDC scores at a follow-up at 8-14 weeks (SMD = 3.70, 95%CI: 0.20 to 7.21, P = 0.04).

BFR in the rehabilitation of TKA patients

Although Chen et al[4] included studies on the role of BFR rehabilitation in improving outcomes after TKA and other procedures, a more focused systematic review and meta-analysis by Tiss et al[12] on TKA included four RCTs involving 148 TKAs patients. All patients received preoperative BFR training for 4-8 weeks, but the training protocols differed across studies. Compared with the control group, only two studies showed significant postoperative improvement in muscle strength in patients who received preoperative BFR training; furthermore, one study demonstrated superior postoperative functional outcomes in patients who received preoperative BFR training.

Jørgensen et al[38] evaluated the effect of preoperative BFR training compared with resistance training in patients undergoing TKA and whether this could improve postoperative function and patient-reported outcome measures (PROMs). They included 86 patients who were randomized into two groups: One group received BFR training for 8 weeks, and a control group that did not receive any preoperative training. The authors observed early (3 months postoperatively) significant improvement in the BFR group compared with the controls in the functional outcomes, using the following 1-repetition maximum leg press and knee extensor strength, maximal isometric contraction for the knee extensors and flexors; however, this significant difference was lost after 12 months postoperatively. Interestingly, there were no significant differences in knee range of motion (ROM), Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales, or Euroqol 5-dimensions (EQ-5D-L5) at any postoperative time points. The results of the previous study suggested that preoperative BFR training for patients undergoing TKA could be beneficial in the early postoperative period; however, this effect was lost after one year postoperatively.

Stroobant et al[39] conducted a study of 45 patients who were dissatisfied with their TKA outcomes. The authors’ primary aim was to evaluate whether adding BFR to the rehabilitation protocol would improve satisfaction and functional outcomes when combined with low-load resistance training for 18 sessions. The authors reported a significant increase in PROMs compared with pre-intervention values. These included the KOOS; the Knee Society Score (satisfaction); the pain catastrophizing scale; the EQ-5D-L5; and functional outcomes measured using the 6-minute walk Test and the 30-second chair stand test. The improvement continued for 6 months of follow-up. The authors concluded that adding BFR to the rehabilitation protocol for dissatisfied patients after TKA improves functional and quality-of-life outcomes.

Various knee procedures

Apart from evaluating the results of implementing BFR rehabilitation protocols for a specific condition or after a specific surgical procedure, some systematic reviews have examined its postoperative effects in patients undergoing various surgical interventions. An example was the systematic review and meta-analysis by Alamri et al[40], in which the authors included 11 RCTs: 7 included patients who had ACLR, 2 included patients who had knee arthroscopy, patients had high tibial osteotomy in one study, and distal radius fracture in another study. Although there was heterogeneity among the included studies, the authors reported that overall muscle strength across all seven studies improved after BFR rehabilitation (SMD = 0.90; 95%CI: 0.44-1.35; I² = 77%; P = 0.0001). A significant increase in muscle size was observed with BFR rehabilitation protocols, as reported across six studies (SMD = 0.74; 95%CI: 0.34-1.14; I² = 46%; P = 0.0003). Interestingly, their analysis failed to show that BFR rehabilitation was superior to the control group without BFR in reducing pain (SMD = 0.33; 95%CI: -1.16-1.82; I² = 94%; P = 0.67). A summary of the various BFR-assisted rehabilitation protocols, pearls, and pitfalls is reported in Table 1.

Table 1 A summary of various blood flow restriction-assisted rehabilitation protocols applied to different knee conditions, their pearls and pitfalls.

		Knee conditions
		ACLR	Knee OA and RA	PFS	TKA
BFR-assisted rehabilitation details	Sets	3 to 5	3 to 5	3 to 5	3 or 4, or until volitional fatigue
	Repetitions	10 or 30/15/15/15 protocol	10 or 30/15/15/15 protocol	10 or 30/15/15/15 protocol	30-15-15-15 protocol
	Frequency	Once to five times weekly	Twice to three times weekly	Twice to three times weekly	Twice to five times weekly
	Duration	2-8 weeks	4-12 weeks	4-12 weeks	6-10 weeks (some advised preoperative sessions)
	Load	30% to 60% RM	20% to 30% RM	30% RM	30% to 80% RM
	Restriction pressure	80% LOP	160-200 mmHg, or 50% to 70% LOP	160-200 mmHg, or 70% LOP	40% to 80% LOP
Pearls to consider	Proper patient selection, and better to avoid its usage in patients with peripheral vascular disease, vascular grafts, and active infection. The tourniquet cuff should be applied as proximally in the thigh as possible. Although there are variations in the used cuff width (ranging from 6 cm to 18 cm), wider cuffs are preferred as they have less potential for causing pain. It is preferable to adjust the tourniquet pressure for each patient [some suggested an equation as follows: Restriction pressure = 0.5 (systolic blood pressure) + 2 (thigh circumference) + 5] or by using ultrasound on the femoral or dorsalis pedis arteries). Limb occlusion pressure should always be tested supine with the patient as still as possible. Most protocols recommend 4 sets of 30, 15, 15, and 15 repetitions with a 30-s rest between sets
Pitfalls and drawbacks to avoid	Using inappropriate pressure will lead to an inability to occlude blood flow. Narrow cuffs may lead to more complications and increased pain after training. High pressure may lead to complications such as nerve injury and limb ischemia. Stop training immediately if the patient feels dizziness, lightheadedness, numbness, or severe pain

ACLR: Anterior cruciate ligament reconstruction; OA: Osteoarthritis; RA: Rheumatoid arthritis; PFS: Patellofemoral syndrome; TKA: Total knee arthroplasty; BFR: Blood flow restriction; RM: Repetition maximum; LOP: Limb occlusion pressure.

What are the possible future directions for increasing BFR utility?

BFR training has shown promising results in the rehabilitation of patients with various knee conditions; however, there is still room for improvement[22,41]. The following are a few points in this regard.

Standardization and personalization: Future protocols should shift away from generic pressure settings toward individualized, automated, and calibrated pressure (e.g., using a percentage of LOP) to ensure safety and effectiveness while reducing the risk of side effects. Specific protocols for BFR application should be well described to facilitate reproducibility, and they should be tailored to each patient’s characteristics. The exact exercise volumes and degree of blood retraction, as well as the safety limits, should be well documented.

Technological advancements

Smart cuffs: Development of devices that can automatically adjust pressure based on real-time feedback of tissue oxygenation or Doppler ultrasound readings.

Combined modalities: Using BFR with electrical stimulation to assist in early rehabilitation where voluntary movement is not possible.

New training modalities

Aerobic BFR: Using BFR during endurance exercises (cycling, walking) rather than just strength training.

Passive BFR: The use of occlusion during rest or immobilization to minimize muscle atrophy in post-surgical patients.

Home-based training: There may be emerging potential for supervised, home-based BFR protocols using automated smart cuffs and tele-rehabilitation platforms, which represent a logical next step for scaling clinical adoption, enabling remote monitoring of occlusion pressures and exercise adherence while vastly reducing patient travel burdens.

Research opportunities: Future well-designed studies are needed to report the long-term results from combining BFR training with other modalities compared to traditional rehabilitation protocols, and eventually to provide the best protocol for each condition, either pre- or postoperatively.

Limitations

The facts and results reported in the current review should be interpreted cautiously, given several significant limitations. First, as this was a minireview designed to provide a brief overview of BFR implementation in the rehabilitation of various knee joint conditions; a detailed literature search and inclusion of all possible evidence were not feasible.

Second, reporting results after treating different conditions and the various tools used to assess outcomes across studies could lead to significant heterogeneity in the included evidence. Notably, the systematic review by Zeitlin et al[42] reported that BFR training resulted in questionable clinically relevant pain improvement and no effect on the quadriceps strength or knee function. These results might be due to the fact that the authors evaluated 15 RCTs that were divided into different conditions: 7 on ACLR, 2 on cartilage surgery, 3 on knee OA, and 3 on PFS, indicating significant heterogeneity of the conditions included in the final evaluation.

Third, we did not discuss the differences in BFR application protocols, including the timing of application, cuff size, and session frequency, which might be crucial for interpreting and understanding the results.

Fourth, the majority of included RCTs and meta-analyses report follow-up periods of ≤ 6 months. Consequently, conclusions regarding long-term maintenance of strength gains, delayed OA progression, or sustained postoperative satisfaction remain premature.

Lastly, some issues were not discussed in detail, such as improved muscle strength, which should not be interpreted in isolation from joint-specific goals, particularly after TKA and ACLR. This is particularly related to the fact that excessive discomfort, swelling, or poorly timed loading may theoretically interfere with range-of-motion restoration or early movement goals; therefore, BFR should be integrated not only in improving muscle strength, but also into a comprehensive rehabilitation program that continues to prioritize pain control, swelling reduction, gait training, progressive ROM, neuromuscular control, and functional milestones.

CONCLUSION

Although the addition of BFR training to rehabilitation protocols for many knee joint-related conditions and elective procedures has shown improvement in patient satisfaction and outcomes with an acceptable safety profile, further research, including well-designed RCTs, especially in the field of knee arthroplasty, is required to delineate its comparative effectiveness relative to traditional rehabilitation protocols, as the current evidence is limited by small sample sizes, short follow-up, heterogeneous protocols, variation in outcome measures, and inconsistent effects on pain. Furthermore, agreement and consensus on the description of BFR training and rehabilitation protocols for each knee condition would facilitate widespread adoption of this technique and enable comparison of results across different reports.