The Biology of ACL Healing: The Wild Card of Recovery

Ligamentization – The Wild Card

One of the most critical steps in ACL reconstruction is grafting a tendon into the knee to replace the damaged ACL. Following surgery, the graft not only has to heal tightly in its new position but also transition structurally from a functioning tendon to a functioning ligament—a process known as ligamentization. Believe it or not, this process takes time! Microscopic studies, in which physicians have taken small samples of healing ligaments following ACL reconstruction to determine their rate of ligamentization, suggest that this process can take anywhere from 6 to 24 months.

The ligamentization process is frustrating because it is an unseen rate limiting step in an athlete’s recovery. Some athletes regain motion, strength, and proprioception at the six-month mark and appear outwardly healed, but the level of ligamentization of their graft is unknown and therefore a return to sport can jeopardize their recovery. For this reason, it is ideal to allow athletes recovering from ACL reconstruction as much time for rehabilitation as logistically possible, assuming it doesn’t jeopardize their return to sport timeline. Many instances of ACL reconstruction failure can be attributed to a failure of graft incorporation and/or the ligamentization process, so giving the athlete adequate time for recovery is best.

One of Dr. Anz’s most passionate clinical research interests revolves around using biologics to improve and/or expedite the ligamentization process following ACL reconstruction. His interest is driven by how critical the ligamentization process is to the full recovery and return to sport of injured athletes. Animal studies have suggested that slower graft incorporation correlates with increased laxity and stiffness, increasing the likelihood of reinjury, and have illustrated improved tendon healing in ACL reconstructions that incorporate the use of stem cell technologies.We theorize that optimization of stem cell technologies for tissue regeneration requires use of the ‘regenerative triad’—a scaffold, stem cells and growth factors. For that reason, regenerative models with ACL reconstruction combine biologic technologies with a scaffold wrap to produce a new “sheet” of cells around the ACL graft.

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There are two studies that illustrate the effectiveness of biologics in improving the rate of ACL maturation. The first of these studies involved injecting leukocyte-poor platelet rich plasma into the fascicles of ACL grafts and the other involved loading of a gelatin carrier with platelet-derived growth factors. Prior to injury, the ACL and PCL are covered by a synovial lining—essentially a layer of collagen that ensures adequate blood and nutrient supply to the ACL. It is now believed that the lack of this synovial lining following traditional ACL reconstruction may delay the process of ligamentization. We believe that the use of a collagen membrane will protect and create as a healing environment like the synovial lining of a healthy joint.

At the Andrews Institute, we believe that collagen membranes can be used to re-establish the natural synovial lining of the ACL. This collagen can also serve as a container to hold biologic adjuncts around the ACL. In 2016, Dr. Anz completed a study determining how many cells can be collected from a patient’s knee, including swelling and by-products of the ACL surgery. This study is helping us to better understand ideal methods for collecting a patient’s stem cells. In early 2017, Dr. Anz hopes to start a human study on biologic augmentation of traditional ACL reconstruction; this study will combine a collagen-wrapped graft tissue with stem cells from the patient’s bone marrow and knee injury fluid.

As an Orthopedic Surgeon and Sports Medicine Specialist, Dr. Adam W. Anz is dedicated to providing individuals and athletes from all over the world with the highest possible quality of care. He serves his patients at the world-class Andrews Institute in Gulf Breeze, Florida. If you have sustained a sports-related injury, please contact our office today and schedule an initial consultation with Dr. Anz or request an appointment online.