The management of ACL injuries took a giant leap in the early to mid 1990’s when Donald Shelbourne and colleagues noticed that patients who didn’t follow doctor’s orders (weeks to months of rest and non weight bearing after an ACL reconstruction) had a much better outcome in the short and long term. Post-operative protocols changed dramatically at the time, allowing people to weight-bear and move much earlier (within a few days to weeks), and this practice continues to this day. Before the change, return to sport was 12-18+ months, now it’s 9-12 months, maybe 6-7 if you’re a professional athlete in the United States (they like to do things quicker there).
Since that time, advances in ACL surgery and rehabilitation have definitely improved the patients’ journey, however return to sport timelines and long-term knee osteoarthritis rates haven’t really changed.
ACL reconstruction (substitution of the ligament) is performed rather than repair. A standard repair of the ACL, where the two torn ends of the ACL are sutured together has shown to be unsuccessful so an ACL reconstruction has been the surgery of choice for decades.
ACL reconstruction using patellar tendon or hamstring tendon grafts are the norm at the moment, and the slow healing and ligamentization of these grafts is the major reason it takes many months to return to sport. Artificial grafts (LARS) can be used in certain circumstances and return to sport can be within a few months, however good quality evidence is lacking on this procedure, and many clinicians are concerned on the long term viability of the artificial graft.
A new surgical technique however has caught the attention of the sports medical community and could revolutionize the management of ACL injuries. The Bridge-Enhanced ACL Repair (BEAR) surgery developed by Boston surgeon Dr Martha Murray uses a sponge bridge to connect the two ends of a torn native ACL.
A special protein infused sponge-bridge is placed in between the two torn ends of the torn ligament, and the sponge is injected with the patient’s own blood to create a clot and a healing scaffold. The surgeon draws the two ends of the torn graft into the sponge, and allows nature to take over and knit the ligament together naturally over time. If you’re finding that hard to visualize, here the link to the video (2 minutes long).
Early research on the BEAR was conducted on pigs, with encouraging results. The ACL repaired well in these animals, and the rate of subsequent arthritis in the knee was also reduced.
Last year (2015) phase 1 human clinical trials were conducted, where 10 patients underwent the BEAR procedure. The ACL repaired in all 10 cases. Phase 2 has started, where Dr Murray has/will enroll 100 patients for a randomized controlled trial. Two-thirds of the participants will undergo the BEAR procedure, with the remainder undergoing a traditional ACL reconstruction. People in the Phase 2 study will be tracked for 10 years.
Clearly it’s early days, and it will take many years for the long-term success or failure of this procedure to be revealed. The procedure may improve return to sport timelines, it may reduce the prevalence of OA in ACL injured knees, and it may improve re-rupture rates, but only time and additional research will tell. I for one will definitely be keeping a close eye how things progress.
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- Shelbourne, K. Donald, and Paul Nitz. "Accelerated rehabilitation after anterior cruciate ligament reconstruction." The American journal of sports medicine 18.3 (1990): 292-299.
- Gäbler, C., et al. "The Introduction of an Artificial Ligament for Reconstruction of the Anterior Cruciate Ligament: A Department's Critical Review of Complications and Problems." Osteosynthesis and Trauma Care 14.01 (2006): 51-53.
- Mastrangelo, Ashley N., et al. "Reduced platelet concentration does not harm PRP effectiveness for ACL repair in a porcine in vivo model." Journal of Orthopaedic Research 29.7 (2011): 1002-1007.
- Proffen, Benedikt L., et al. "Bridge-Enhanced ACL Repair: A Review of the Science and the Pathway Through FDA Investigational Device Approval." Annals of biomedical engineering 43.3 (2015): 805-818.