Last week, The Boston Globe reported that Martha Murray, MD, an orthopaedist at Boston Children’s Hospital, had announced results from the Phase 1 safety study of “bridge-enhanced” ACL repair, which OrthoBuzz first told you about in April 2015 (see “ACL Self-Repair Moving Toward Reality”). According to the Globe, “all 10 BEAR [Bridge-Enhanced ACL Repair] patients…have new, healthy ACLs regrowing where there were originally tears.”
The Globe article quoted Jo Hannafin, MD, past president of the American Orthopaedic Society for Sports Medicine (AOSSM), as saying that BEAR “has the potential to be a game-changer.” But Dr. Hannifin was quick to add that “these patients will have to be followed for a minimum of two years to determine whether the ACL heals and does that healed ACL stay competent or stretch over time and fail.”
Another key question is how much arthritis will develop in the BEAR knees 15 or 20 years from now. In preclinical studies of BEAR on pigs’ knees, the rates of subsequent knee arthritis were lower than those seen with traditional reconstruction techniques.
The Globe reported that Dr. Murray will start enrolling 100 patients for a Phase 2 randomized trial this summer. She will be seeking people from 14 to 35 years of age with torn ACLs that occur within 30 days of enrollment. Additional inclusion criteria include a tibial ligament stump that is at least 6 to 8 mm in length and no serious concomitant knee damage. Two-thirds of the Phase 2 study enrollees will be randomized to undergo the BEAR procedure, and the other group will undergo traditional ACL reconstruction. Patients will be followed for up to 10 years to assess the competence of the repair and track the development of arthritis.
OrthoBuzz will keep you posted on this important ongoing research.
OrthoBuzz has been following the development of the Bridge-Enhanced ACL Repair (BEAR) implant—a synthetic alternative to graft-based anterior cruciate ligament reconstruction—since 2015 (see previous OrthoBuzz posts). On December 16, 2020 the FDA granted authorization to Miach Orthopaedics, Inc. to market the implant.
The BEAR implant is made from bovine collagen. After securing it with sutures to the torn ends of a completely ruptured ACL, the surgeon injects the patient’s own blood into the implant, which forms a clot that enhances ligament healing. Within 8 weeks, the implant is resorbed and replaced by the body’s own tissue.
The FDA’s authorization was based on results from a 100-patient randomized clinical trial, in which 65 patients received the BEAR implant and 35 underwent conventional autograft reconstruction. After 2 years, patient-reported outcomes in both groups were similar for pain, knee function, and sports activity, and arthrometry showed nearly identical joint-laxity outcomes. It remains to be seen how durable the BEAR implant will be over time and how much arthritis will develop in BEAR-treated knees 15 or 20 years from now.
The FDA’s marketing authorization for the BEAR implant was granted under the agency’s de novo device review pathway. That means that subsequent similar devices can be reviewed through the FDA’s 510(k) process, which requires a demonstration of “substantial equivalence” to the predicate device.
Attempts by orthopaedists to repair torn human ACLs have failed for the most part, so surgeons now rely almost exclusively on removing the torn ligament and replacing it with autograft or allograft tissue. But now research at Harvard by Martha Murray, MD—a co-author of several JBJS studies—suggests that a torn ACL can be prompted to repair itself.
As Dr. Murray explains in a video, “bridge-enhanced” ACL repair uses stitches and a spongy scaffold injected with the patient’s blood placed between the torn ends of the ACL. The bridge helps healing clots to form and helps surrounding cells grow to rejoin the ends of the ligament. Preclinical studies using this technique have resulted in successful ACL repairs and rates of subsequent knee arthritis that were lower than those seen with reconstruction techniques. Bridge-enhanced ACL repair would also eliminate the need for tissue harvesting in the many patients who choose the autograft reconstruction option.
After reviewing the data from the preclinical studies, the FDA approved the first safety study of this technique in humans, which is now underway.