For patients with a torn ACL, the surgeon’s goal is to return the patient’s knee and function as close as possible to its original, natural state with minimal disruption to their anatomy.

Although most tissue is repaired through the body’s natural healing process, unfortunately the ACL’s natural response to injury limits its ability to self-heal. At least until recently, the best option to repair ACL tears has been ACL reconstruction (ACLR). ACLR requires the damaged ACL to be removed and replaced with a donor ligament – either from the patient’s own tissue or a cadaver. Although ACLR is effective, the procedure has drawbacks. In addition to graft site morbidity, many people are unable to return to the same level of daily activities or sports.

Fortunately, a new treatment option enables the body to heal its torn ACL, returning it to its original, natural state with minimal disruption.

The Healing Response: Most Tissue Heals by Itself

When tissue is injured – whether it be skin, muscle, or even certain ligaments – it goes through a four-phase healing cascade to repair the damaged area:

• Hemostasis/Inflammation: Bleeding is stopped through the formation of a blood clot. Inflammation occurs as white blood cells flood the area to remove debris and protect the body from infection.
• Epithelialization: Epithelial cells are laid down and the wound is closed.
• Proliferation: Fibroblasts lay down granulation tissue, including collagen, to create a new bed of tissue.
• Remodeling: Collagen matures into a scaffold for the formation of new tissue and blood vessels, and the tissue is remodeled to regain strength and flexibility.

How the ACL’s Response Limits its Healing Potential

Although the torn ACL has a similar response, key differences limit its ability to heal. 

The inflammatory phase still upregulates white blood cells and clotting factors, but a clot is unable to form due to the presence of synovial fluid in the joint. As a result, there is no clot or tissue to bridge the site of injury. The ACL then undergoes repair, in which the epiligament, or connective tissue lining the ligament, and synovial tissue form over the torn end of the ACL. The proliferative phase results in encapsulation of the ACL stump with a synovial sheath, followed by remodeling and retraction of the stump that closes it off completely from the surrounding tissue. 

In other words, unlike the healing process for most tissues, the ACL’s response does not include a clot or tissue that can bridge the site of injury and serve as a scaffold for the formation of new tissue and blood vessels.

What Prevents Clot Formation in the ACL Healing Process?

In a normal healing reaction, thrombin is released at the site of injury and cleaves fibrinogen in the blood. This results in fibrin, a sticky protein that collects red blood cells to form a provisional scaffold or clot to allow the start of the healing cascade.

In an ACL tear, plasmin present in the synovial fluid breaks down the fibrin clot, resulting in bleeding in the knee joint. Without a provisional scaffold to continue the healing response, the ligament undergoes epiligamentous repair and eventual contraction. 

Creating a Healing Environment to Restore the ACL

While all of the phases of the healing response are present in ACL tears, it lacks the critical step of clot formation and the presence of a scaffold. Is there a way to encourage healing in this unfavorable environment and provide a stable clot and provisional scaffold to bridge the gap between the torn ends of the ACL?

Such an approach would need to prevent synovial fluid from breaking down the fibrin clot, which is essential to bridge the gap between the torn ends of the ACL. Overall, a solution must be able to:

• Absorb, hold and protect blood from synovial fluid
• Support a scaffold that is biocompatible, highly porous and limit the immune response
• Allow the use of whole blood to stimulate ACL growth
• Support cell migration, proliferation, and vascularization

The BEAR Implant

The only available solution that meets these criteria is the BEAR Implant – a bridge designed to restore the native ACL. The BEAR (Bridge Enhanced ACL Restoration) Implant is a decellularized, bovine-derived, type I collagen implant. During the procedure, the surgeon adds the patient’s blood to the BEAR Implant and inserts it between the torn ACL ends. The implant holds and protects the blood to allow the formation of a clot.

The BEAR Implant:

• Resists plasmin degradation by being hydrophilic, able to absorb, hold and protect the patient’s blood from synovial fluid, and hemostatic by allowing a clot to form in the gap between the ACL ends
• Limits the body’s immune response by removing cellular material during processing and does not contain chemical cross-linking agents
• Encourages ACL cell in-growth and proliferation and is highly porous

Healing Validated by MRI and Histology

The BEAR Implant helps heal the ACL by facilitating the body’s own healing response by supporting cell migration and proliferation. Within eight weeks, the BEAR Implant is resorbed and replaced with native cells, collagen and blood vessels. The new tissue continues to remodel and strengthen over time.

The BEAR Implant can be surgically placed during an outpatient procedure that helps the patient’s ACL heal to a size and quality similar to what it was before the injury, retaining the normal anatomy and function of the knee, according to a 2016 study published in the Orthopedic Journal of Sports Medicine. Compared to grafts, it does not require a second surgical wound site to remove a healthy tendon from another part of the body or use a deceased donor’s tendon. In addition, it results in a faster recovery of muscle strength and higher patient satisfaction with regard to readiness to return to sports, according to a 2022 study.

The BEAR Implant is backed by Level 1 clinical evidence and was cleared by the U.S. Food & Drug Administration through the De Novo Pathway in December 2020. It is indicated for skeletally mature patients at least 14 years of age with a complete rupture of the ACL, as confirmed by MRI.

By enabling the torn ACL patient’s body to naturally heal itself, the BEAR Implant meets the goal of returning the patient’s knee and function as closely as possible to its original, natural state with minimal disruption to their anatomy.

Learn More About the BEAR Implant

Visit www.miachortho.com for complete product information, including Instructions for Use.

ML-1194 Rev A 06/2024