All staff participating in the study no longer employed by organization.

The purpose of this study is to look at the effects of bone density on lower extremity loading mechanics using Blood Flow Restriction (BFR) to provide the control group for bone health.

Hypothesis: The BFR group will have decreased bone mineral loss and improved functional performance compared to control group.

Group 1 - ACL without BFR : 30 athletes with ACL tears and will NOT do blood flow restriction (BFR). Random group allocation will be determined using envelopes for allocation concealment. The control group will be tested with a Dexascan immediately post appointment confirming MRI findings of ACL tear and scheduling surgery. They will be then Scanned again at first therapy appointment within 24-48 hours of surgery. Then Dexascans will be done every 4 weeks until 28 weeks with a maximum of 9 scans. The scans will be completed on a normally scheduled rehabilitation session at the convenience of the radiology techs availability. The investigators will collect force plate measurements for squat symmetry at first 4-week assessment period, and then for landing symmetry every 4 weeks after that until 28 weeks.

Group 2 - ACL with BFR: 30 athletes with ACL tear that will receive BFR. This group will be selected in the same manner as the control group. They will be tested with a dexasan immediately post appointment confirming MRI findings of ACL tear and scheduling surgery. At the initial dexascan they will also be instructed in Blood flow restriction and do exercises with blood flow restriction to prepare for initial post-surgical visit. They will be then scanned again at first therapy appointment within 24-48 hours of surgery. Then Dexascans will be done every 4 weeks until 28 weeks with a maximum of 9 scans. The investigators will collect force plate measurements for squat symmetry at first 4-week assessment and then for landing symmetry every 4 weeks after that until 28 weeks.

The standard of care following ACL tear does not include Dexascan, force plate measurements, or blood flow restriction.

Independent Variable

1. Blood Flow Restrictions (BFR) Dependent Variable

1. Landing mechanics / force distribution
2. Bone Mineral Density /Bone mass
3. Lean Muscle Mass (LM)
4. Pain via Visual Analogue Scale (VAS)
5. Quad Strength using microFET®2 Digital Handheld Dynamometer
6. Hamstring strength using microFET®2 Digital Handheld Dynamometer
7. SL Hop Distance
8. Triple Hop Distance
9. Crossover hop Distance
10. Keiser leg press max power at 5 reps at body weight

Procedures: Once a participant has been identified as meeting the inclusion criteria with a positive MRI finding and have agreed to schedule surgery, they will be allocated to either the control or experimental group. Random group allocation will be determined using envelopes for allocation concealment. Prior to initiation of the study, a research assistant not involved in data collection will use a random number generator to create the randomization sequence allocating an equal number of participants to each of the 2 groups, the control non BFR group and the experimental BFR group. The randomization will be concealed by having the group assignment placed inside a sealed opaque envelope within potential participant folders. This process will be documented and signed by the randomizer. Once selected and enrolled, the group assignment will be revealed and will not be blinded to either the participant or the researchers. The pre-op therapy session will be completed 48-72 hours following MRI confirmation of ACL tear if they have opted for surgical intervention. The initial post-op therapy session will be completed within 24-48 hours of surgery.

All participants will undergo bone mineral density (BMD), bone mass, and lean muscle mass (LM) measurements using Dexascan at pre-op visit, and again at initial post op visit ad then every 4 weeks from week 4-16.

Participants will also complete a total of 9 landing/jumping trials as part of testing, with rest as needed. Following the warm-up, subjects will complete 3 drop landings, 3 drop vertical jumps, and 3 countermovement jumps. The participant must demonstrate safe landing mechanics on the drop landings as determined by testing PT in order to attempt the drop vertical jumps and the countermovement jumps.

Landing assessment will be collected at initial landing session at weeks 8, 12,16,20, 24, and 28 weeks post op.

The exercises selection and progression will be standardized for BFR intervention across all subjects. The BFR group will exercise with 80% arterial limb occlusion using the Delphi automated tourniquet around the proximal thigh outfitted with Doppler (Delfi®). If 80% arterial limb occlusion is not tolerated by the participant, the pressure will be decreased to tolerance. However, the pressure will not be lowered below 60% as there is a floor effect at 60% LOP where BFR is no longer beneficial.

Exercises will be performed for 4 sets of 30-15-15-15 repetitions separated by 30s of rest and 1 BFR exercise will be performed. SL hop, Triple hop, Crossover hop, and Keiser leg press power will be measured at 12, 16, 20 and 24 weeks. Strength testing will be done with microFET®2 Digital Handheld Dynamometer every 2 weeks of the rehab process in accordance with standard rehab protocol.

Inclusion Criteria:

• Athletes undergoing ACL reconstruction with or without meniscal pathology
• MRI confirming ACL tear
• Athletes ages 16-22

Exclusion Criteria:

• Any Cognitively impaired athletes
• Athletes not in age range of 16-22
• Athletes who have additional ligament repair or chondral repair.
• Athletes with any weight bearing restrictions greater than 4 weeks.
• Athletes with re-tears or history of contralateral ACL tears
• Athletes with any systemic neuromuscular or balance disorders will not be allowed
• Athletes who do not or are unable to provide consent or assent (with Parental consent).
• Pregnant women will be excluded.
• Athlete who has previously used Blood Flow Restriction
• Athletes who are unable or unwilling to complete all rehabilitation with Parkview Athletic Rehab at SportONE Parkview Fieldhouse