THE FUTURE OF ACL RECONSTRUCTION

BY ANA MEHRANIAN – It was the first game of the 2008 NFL season and the Patriots were playing the Kansas City Chiefs. A heavy blow to the knee later, and Tom Brady was walked off the field with a season-ending injury. The impact left his left anterior cruciate ligament (ACL) completely torn. A strong return eight months later earned him the 2009 NFL Comeback Player of the Year. An ACL tear is a serious injury that can sideline professional athletes to a weekend warriors alike.

Ligaments are long, stringy fibers of connective tissue, composed primarily of collagen. These elastic fibers come together to form tough yet flexible bands. Ligaments play an important role in the body, connecting bone to bone and providing skeletal stability. Although ligaments are capable of withstanding a certain amount of gradual stretching; sudden and sharp movements can be dangerous. When a ligament becomes overstretched, the integrity of its structure and function is compromised. Landing improperly from a jump, rapidly changing direction, pivoting without moving the foot, or direct blows to the knee are a few examples of motions that can result in injury to ligaments in the knee.

One of the most common knee injuries, an injury to the ACL, is a stretch, strain, or tear to the ligament. The cruciate ligaments are two of the four primary ligaments in the knee, providing the joint with stability. The ACL prevents your tibia from moving too far forward, as well as providing the joint with rotational and lateral stability. Damage to the ACL usually results in a partial or complete tear, although in mild injuries, may only be a strain to the ligament. The path to recovery varies patient to patient, in young and active individuals, reconstructive surgery is usually recommended.

Due to the flow of synovial fluids in the knee, the ACL cannot repair itself (in complete tears), even if the torn ends are reconnected. The continual flow of synovial fluid disperses the blood throughout the knee joint, preventing the formation of a blood clot at the wound site. Blood clots act as scaffolds upon which the body builds bridges of collagen to reconnect and ultimately heal torn ligaments. The lack of localized blood flow also deprives the damaged ligament of proteins, nutrients, and other substances required in the healing process.

Surgical repair of the ACL is achieved with the securement of a graft in place of the native ligament. The most common techniques include patellar tendon, hamstring tendon, and donor tissue grafts. Patients who undergo current surgical treatments for ACL injuries have a notoriously high risk of developing osteoarthritis within a decade of injury. Specifically, up to 80% of patients will develop the joint disease within fifteen to twenty years. After surgery, patients are not always able to return to their pre-injury activity level, and are at a high risk of a second knee injury as well.

The Bridge-Enhanced ACL Repair (BEAR) scaffold was originally manufactured at Boston Children’s Hospital as an alternative to the traditional approach to reconstructive surgery. The new technique uses a sponge injected with the patient’s blood to create a bridging scaffold to heal the torn ligament. Current clinical trials have shown that the technique is successful. Magnetic resonance images from all patients treated with BEAR demonstrated an intact graft. Additionally, hamstring strength at 3 months post-op was significantly better in BEAR patients than in those who received traditional surgical reconstructions. If the BEAR trials continue to show positive results, the technique may become a widespread option for ACL repair within the next few years, boasting a quicker healing time, a lower risk of developing post-traumatic osteoarthritis, and a lessened risk of re-injury.