Effect of low load Blood Flow Restriction (BFR) exercise on postoperative outcomes after knee ligament reconstruction

Blood Flow Restriction (BFR) training will be the intervention applied to the treatment arm of this trial. Pressure will be set to 80 percent limb occlusion pressure (LOP) at rest. Patients randomized to the BFR cohort receive personalized limb occlusion pressure (LOP) measured using a Doppler ultrasound placed on the dorsalis pedis pulse by the physiotherapist administering the BFR. The LOP will be checked every 2 weeks. Patients in the BFR group are provided a single-chamber manual pneumatic torniquet (BFR.co) when performing pre-habilitation exercises. The limb occlusion pressure should be set to 80% unless the participant reports undesirable pain scores (>5 on a 10 point visual analog scale) associated with the starting cuff pressure around the thigh, then the pressure should be reduced in 10% increments until VAS pain scores are a 5 or less. LOC below 50% would trigger an exclusion of the patient from the BFR study as ‘cuff intolerance’. Before surgery, all patients indeterminant of treatment group will complete a home exercise program by a physiotherapist. The home exercise program consisted of exercises performed 5 times a week for the 2 weeks before surgery as a form of ‘‘prehabilitation.’’ Exercises included quadriceps contractions in end-range extension, straight-leg raises, long-arc quadriceps sets, and quarter squats. All exercises were performed for 75 repetitions with a repetition scheme of 30-15-15-15, allowing for 30 seconds of rest between sets. Patients were educated on how to properly perform the required exercises and were asked to sign a log (exercise diary) that would be returned during the preoperative visit to demonstrate compliance. BFR training will occur twice weekly beginning 2 weeks following surgery and concluding at 12 weeks post operatively. The BFR training will be carried out in accordance with a 2020 study (Humes et al., 2020). In utilizing BFR therapy, a standard postoperative rehabilitation protocol will be implemented following the guidelines outlined in the Melbourne ACL Rehabilitation Guide. The pneumatic cuff will be placed more proximal than distal to mitigate neurovascular injury. In addition, for the traditional strengthening BFR exercises, four sets should be performed with reps of 30/15/15/15 including 30 second rest interval between each set with the BFR cuff still inflated. After the completion of exercise, the cuff is deflated for one minute to allow for reperfusion before continuing with the strengthening exercise. The load resistance would be determined preoperatively at 30 percent of maximum resistance during 1 repetition (1RM). At the 3-month mark, patients were progressed to usual heavy-resistance training and BFR was discontinued. Instead of using percentage repetition maximum, the loads will be adjusted within the first session to meet either the desired repetition scheme or time under tension. A brief description of the postoperative rehabilitation protocol is as follows: Phase One – 0-6 Weeks Overview: Phase One, the protected phase, starts in the first week post-op (after day three). Goals include pain control, reducing joint effusion, restoring range of motion, and maintaining muscular and aerobic endurance. BFR Usage: Max 25 minutes. The participants are only required to wear the cuff during the rehabilitation sessions. Exercises are divided into three subsets: weeks 1-2, weeks 2-4, and weeks 4-6. Weeks 1-2: Neuromuscular Electrical Stimulation: 10-20% max voluntary contraction for 10 minutes (10 sec contraction, 20 sec rest). Pads placed on vastus lateralis and vastus medialis oblique. Exercises: Isometric holds (60-90 degrees flexion). Hip adduction (initially no weights, then cuff weights). Bent knee ankle plantar flexion (increase resistance as tolerated). Straight leg raises (begin with no weights, add cuff weights as needed). Weeks 2-4: Continue previous exercises unchanged. New Exercises: Prone hip extension (initially no weights, then cuff weights). Long arc quad (30-90 degrees, no weights until week four). Weeks 4-6: Continue straight leg raises, side-lying hip abduction, and long arc quad with same protocols. New Exercises: Bilateral bridging (avoid joint line pain). Leg presses (0-60 degrees, 25% body weight). Phase Two – 6-12 Weeks Focus: Strengthening for normal weight-bearing gait and full range of motion. Exercises at ~30% of one-rep max to prevent atrophy and promote hypertrophy. Weeks 6-10: Exercises: Leg presses (25% body weight or 30% one-rep max). Resisted hamstring curls (30% one-rep max). Exercise bike (15 minutes at resistance level 3). Weeks 10-12: Continue exercise bike for endurance. New Exercises: Squatting (regular and split) at 30% one-rep max. Phase Three – After 12 Weeks (up to 24 weeks post-operative) Transition: Begins at three months post-ACL reconstruction, moving from HIIT to BFR training until HIIT can be done without pain. Gradually wean off BFR until exclusively performing HIIT. Direct observation of the participants during their rehabilitation sessions will be carried out by the treating physiotherapist in order to assess and monitor adherence. The overall trial duration will be 24 weeks.