Update on ACL Injuries and Treatment

The ACL Study Group meets every two years to update the latest knowledge on ACL injuries and treatments. This year’s meeting was at the base of the Hahnenkamm ski race in Kitzbuhel Austria—the most famous downhill ski race on the World Cup circuit. One hundred and fifty of the world’s top ACL surgeons watched 30 of the world’s bravest ski racers hurtle down the ice-crusted hill at 140 km/h (84 mph). The outcome of the race was predictable: The Austrians dominated. The outcome of the scientific meeting, however, was less conclusive; the ACL is still a tough problem to solve.

ACL Study Group 2020 Hahnenkamm, Austria

Here are some highlights, in my view, of the latest work presented on ACL Injuries:

  1. The ruptured ACL is very commonly associated with other injuries—such as meniscus tears, damage to the outside ligamentous structures, or bone and articular cartilage impact injuries—all of which must be effectively treated or arthritis will occur in 50% of patients.

  2. To diminish the likelihood of arthritis, meniscus tears must be repaired, rather than removed; the articular cartilage must be repaired, not shaved down; and the supporting ligaments around the knee must also be repaired (though there is considerable debate about the best way to do this). Extra articular ligament reconstruction—once very common, then mostly abandoned during the 1990s—has made a strong comeback. This likely results from the realization that an ACL is rarely torn in isolation and reconstructing it alone does not provide full stability to the knee.

  3. The choice of tissue—whether to use a patellar tendon, quadriceps tendon, a hamstring tendon from the patient, or donor tissue from tissue bank—has not been resolved. Most surgeons do acknowledge that they use the best tissue, bone patella tendon bone, for their highest performing athletes. The longest, largest single study of ACL outcomes, with the best results, was conducted using the patellar tendon.[i] It, therefore, remains unclear why a surgeon would use a hamstring tendon—except for that was just the way that he or she was taught. In our own experience, there has been no difference in outcome whether we took the patellar tendon from the patient, or received it from the tissue bank. So we see no reason to further harm the patient by harvesting their tissue.

  4. Surgical technique still matters. There are far too many ligaments being placed non-anatomically, usually too high in the femoral notch. This is partly due to surgeon training, and partly due to the use of instrumentation that is not ideal for every patient.

  5. Rehabilitation after surgery may matter the most. The failure to regain full motion, especially extension, equal to the opposite side of the patient’s body, is the single non-operative risk factor leading to knee pain and low return to full sports. The critical window for regaining that full extension is within the first two weeks. Daily physical therapy, sometimes augmented by a knee extension device, may be the least expensive therapeutic and prophylactic treatment.

  6. Children remain a high liability for sports knee injuries, with a 30% revision rate. Girls still have the highest repeat ACL tear rate of any group, in both their operated and their non-operated knee. There remains a debate about whether to use allograft (donor) patellar tendons in children, as one large study showed a higher failure rate with allografts over the patient’s own tissue.[ii][iii] In my own hands—given how the high rate of failure for any procedure with children—I would rather not sacrifice their tissue to rebuild their knee.  If they fail an allograft, I can always put in another. If they fail their own tissue reconstruction, the options become more and more destructive.

  7. ACL repair rather than reconstruction is again under review. One study shows that if you enhance the natural blood clot formed at the top of the ligament rupture with a collagen scaffold, and repair it with sutures, the ACL can heal.[iv] Unfortunately, most surgeons believe (correctly) that when the ACL ruptures, it fails throughout the ligament. Thus, just inducing healing at the top with a repair may not be an enduring way to fix the problem. In the past, most ACL repair techniques looked great at two years but awful at five years—which is why they were mostly abandoned. There remain some partial tears that can be successfully repaired today.

  8. ACL prevention. Injury prevention works. However, it must become ubiquitous among coaches and trainers to have the desired effect. All athletes and teams can be taught with ACL injury prevention programs, which are free online and significantly reduce their risk of ACL injuries.

  9. Growth factor and stem cell recruitment injections of hyaluronic acid and amniotic fluid were shown to reduce symptoms and improve activities in osteoarthritic (OA) knees. Since OA is still such an unsolved problem after an ACL injury, the future may lie in regular injections of these factors to modify the biochemical changes that occur in the knee as a result of an injury. 

  10. Ski racing, especially at the Hahnenkamm is a high-injury sport—as is skiing in general. The problem of ski bindings has not been solved. But basketball, soccer, rugby, and football also contribute more than their fair share of ACL injuries. Since we all want to play, and have our children play too, we are motivated to prevent these injuries through training, education, and equipment improvements. 

When there is any injury, our goal should be to repair the knee considering the whole person, and not just the ligament. Now, if only the post-race schnapps would open the doors to magical revelations about how to regrow normal body parts immediately after injury….


ACL Reconstruction Surgery Explained & Picking The Right ACL Graft


[i] Shelbourne, K. & Benner, Rodney & Gray, Tinker. (2017). Results of Anterior Cruciate Ligament Reconstruction With Patellar Tendon Autografts: Objective Factors Associated With the Development of Osteoarthritis at 20 to 33 Years After Surgery. The American Journal of Sports Medicine. 45. 10.1177/0363546517718827.

[ii] Kane, Patrick & Wascher, Jocelyn & Dodson, Christopher & Hammoud, Sommer & Cohen, Steven & Ciccotti, Michael. (2016). Anterior cruciate ligament reconstruction with bone-patellar tendon-bone autograft versus allograft in skeletally mature patients aged 25 years or younger. Knee Surgery, Sports Traumatology, Arthroscopy. 24. 10.1007/s00167-016-4213-z.

[iii] Maletis, Gregory & Chen, Jason & Inacio, Maria & Love, Rebecca & Funahashi, Tadashi. (2017). Increased Risk of Revision After Anterior Cruciate Ligament Reconstruction With Bone–Patellar Tendon–Bone Allografts Compared With Autografts. The American Journal of Sports Medicine. 45. 036354651769038. 10.1177/0363546517690386.

[iv] Murray, Martha & Kalish, Leslie & Fleming, Braden & Flutie, Brett & Thurber, Laura & Freiberger, Christina & Henderson, Rachael & Perrone, Gabriel & Proffen, Benedikt & Kramer, Dennis & Yen, Yi-Meng & Micheli, Lyle. (2019). Bridge-Enhanced ACL Repair: Two Year Results of the First In Human Study. Orthopaedic Journal of Sports Medicine. 7. 10.1177/2325967119S00197.

Medically authored by
Kevin R. Stone, MD
Orthopaedic surgeon, clinician, scientist, inventor, and founder of multiple companies. Dr. Stone was trained at Harvard University in internal medicine and orthopaedic surgery and at Stanford University in general surgery.