What if the anterior cruciate ligament (ACL) had the ability to repair itself? The ACL, a ligament located with the knee, is the tissue responsible for bridging the shinbone to the thigh bone. “Torn ACLs are among the most common knee injuries in the United States,” according to Capt. Raquel Peat PhD [1]. Annually in the United States, as many as 250,000 people suffer an ACL tear [2]. Bridge-Enhanced ACL Restoration, or BEAR for short, is a state-of-the-art innovation that will forever change how ACL tears are treated.
A fully torn ligament is referred to as a grade three tear. While a few ligaments are able to heal on their own, most tears of this magnitude, including a torn ACL, aren’t able to heal naturally. Upon suffering a grade three tear the injured tissue disconnects from the body's blood supply so surgery becomes necessary. In the case of a grade three ACL tear, the injured individual will require a full reconstruction of the ligament. ACL reconstruction surgery consists of the removal of the torn ligament, followed by the insertion of a donor tendon [3]. While the donor tendon can come from a deceased individual, it’s most common to have the donor tendon taken from the injured patient. The process of connecting the gap caused by the ACL tear through the utilization of a donor tendon is known as tendon grafting [4]. ACL reconstruction surgery via tendon grafting became prominent in the mid-1980s and has since served as the standard of treatment [5].
Despite the effectiveness of ACL reconstruction surgery, the surgical procedure can lead to recovery complications. Moreover, the procedure has been associated with a high risk of arthritis developing in the injured knee [5]. After having gone through ACL reconstructive surgery many patients are unable to return to their previous level of daily activities or sports [6]. The most prominent complication that arises from ACL reconstruction surgery appears in the healing of surgical sites. Since the injured patient is often the tendon graft donor, the patient will have to recover from the incision to rehabilitate the ACL as well as the incision to seize the tendon graft.
Unfortunately, the ACL is a ligament which is unable to heal on its own, because of synovial fluid present within the knee. Synovial fluid is responsible for reducing the friction between bones at the knee joint [6]. While the fluid is essential to proper operation of the joint, synovial fluid inhibits the formation of blood clots which would be necessary for the ACL to mend naturally.
For decades, orthopedic specialists have been attempting to create a pathway that would allow a torn ACL to heal on its own. Dr. Martha Murray, orthopedic surgeon-in-chief at Boston Children’s Hospital, achieved a breakthrough with the creation of BEAR. Within the BEAR operation, a blood-infused, protein-based sponge is inserted between the ends of the torn ACL. The blood infused within the sponge is taken from the patient, and is used to promote the reconnection of the ACL to the sponge and, ultimately, to one another [7]. Simply stated, the BEAR implant acts as a bridge to assist the ACL to heal under its own power. In addition to only requiring one surgical site, benefits of the BEAR implant include faster recovery of muscle strength and higher patient satisfaction [6].
In the spring of 2019, Dr. Murray and her team conducted a study with the intention of comparing results between patients who underwent ACL reconstruction surgery against patients who were treated through BEAR. Results were scored according to a baseline provided by the International Knee Documentation Committee. 44% of patients in the BEAR group scored an A (normal) grade, indicating their knee was fully repaired from the tear, while 29% of the patients who had ACL reconstructive surgery received an A grade [8]. Furthermore, hamstring strength indices were significantly higher in the BEAR group compared with their counterpart [8].
On Dec. 16th, 2020, the U.S. Food and Drug Administration (FDA) granted marketing authorization for BEAR as an alternative way to treat a torn ACL. The FDA reviewed the BEAR implant through the De Novo premarket review pathway, a regulatory pathway for low- to moderate-risk devices of a new type [1]. Upon FDA marketing approval, Murray discussed how her journey has highlighted the value of serving as a physician-researcher. “When you’re faced with a patient with a problem and the current solution is imperfect, it’s great to be able to say, ‘We’re working on a better solution.’ It’s incredibly gratifying.” To be a candidate for the BEAR implant one must both be at least 14, and one must undergo the surgery within 50 days of their ACL tear [6].
References
1. U.S. Food & Drug Administration. (2020). FDA authorizes marketing of a new implant to repair a torn ACL.
https://www.fda.gov/news-events/press-announcements/fda-authorizes-marketin g-new-implant-repair-torn-acl
2. Runyan C. (2014). Funded Injury Control Research Centers (ICRCs). Centers for Disease Control and Prevention.
https://www.cdc.gov/injury/erpo/icrc/2009/1-R49-CE001495-01.html.
3. Minnesota Valley Surgery Center. (2021). Can torn ligaments heal on their own? When to consider surgery.
https://minnesotavalleysurgerycenter.com/orthopedic-surgery/can-torn-ligaments heal-on-their-own-when-to-consider-surgery/
4. Prodromos, C.C., & Hecker, A. (2017). Whipstitch-post tibial fixation for anterior cruciate ligament reconstruction. The anterior cruciate ligament (2nd ed.). https://www.sciencedirect.com/science/article/pii/B9780323389624000783
5. Murray, M.M., & Fleming, B.C. (2020). Bridge-Enhanced Anterior Cruciate Ligament Repair is not inferior to autograft anterior cruciate ligament reconstruction at 2 years: Results of a prospective randomized clinical trial. The American Journal of Sports Medicine.
https://journals.sagepub.com/doi/full/10.1177/0363546520913532
6. Miach Orthopaedics. (2022). BEAR implant.
https://miachortho.com/patients-and-families/bear-implant/
7. Weiner, S. (2021). 8 medical advances that you may have missed during COVID-19. AAMC.
https://www.aamc.org/news-insights/8-medical-advances-you-may-have-missed during-covid-19
8. Murrary, M.M., Kalish, L.A. (2019). Bridge-Enhanced Anterior Cruciate Ligament Repair: two-year results of a first-in-human study. Orthopedic Journal of Sports Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6431773/
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