Spontaneous Healing of the ACL

11/11/2022

Good Friday to you all! In the past week a very interesting piece of research came out of the British Journal of Sports Medicine about ACL injury. The findings are very much unexpected and worth discussing as ACL injury while uncommon has significant effects. So, let’s dive into it!

This study comes from the KANON trial in Sweden looking at the best rehabilitation approach for ACL rupture. For those that are unfamiliar with ACL injury a brief few points:

  • The ACL is a ligament within the knee which has an important role for keeping the knee stable
  • An injury to the ACL is most likely to occur during a sporting activity of high speed and force. It is typically associated with landing and/or changing direction at speed. Direct contact to the leg with the foot planted can also cause injury although it’s less common
  • Some of the typical signs of ACL injury include; significant pain instantly that eases within a few minutes, significant swelling and bruising, difficulty with taking weight on the injured side initially and a feeling of the knee being unstable with turning or sudden movements
  • Other injury is often spotted on MRI following an ACL injury, whether it has occurred before or with the injury is unclear
  • Unfortunately for people who have an ACL injury or rupture they are more likely to develop osteoarthritis, particularly if there rehabilitation is deficient in certain areas

So the KANON study divided people with an ACL rupture into 2 groups. The first had an immediate surgical repair and physiotherapy based rehabilitation. The second group had rehabilitation first and could opt for surgery if they were not satisfied with progress. The researchers re-evaluated both groups after 2 years and 5 years. This is very helpful as it provides a long-term perspective on the effects of both approaches. 

By the 5 year mark 51% of people in the rehabilitation group had decided to have surgery, which means approximately 75% of participants had surgery in the end. Of the 25% who did not have surgery nearly 60% showed some or complete healing of the ACL, and this started to become evident as early as 3 months. To my knowledge, this is a very novel finding. It had been previously believed that a ruptured ligament could not heal unless the torn ends were brought back together through surgery or prolonged immobilisation. The authors suggest a few reasons why the ligament may have healed “spontaneously”:

  • the tear was in an area of the ligament with very good blood supply
  • that some of the ACL fibres were still intact but this was not seen on MRI
  • that the lining around the ACL remained intact which held it together 

The other interesting finding is that those that remained in the rehabilitation group at both 2 and 5 years rated their ability to participate in sporting/recreational activity and their quality of life as better than those who had surgery. This may be explained in part by the severity of injury being higher in the surgery group, or at least those who elected to have it. 

Overall while the results are very promising, and suggest it may be valuable to undertake 2-3 months of conservative rehabilitation (including immobilisation of the knee), before deciding on surgery, this is the first study of it’s kind, and it is unlikely to change early management of ACL rupture. As ever with research we will need further studies, and I hope they will focus on identifying who definitely needs surgery and who has the potential to recover without it. It is well recognised that if surgery can be avoided, we avoid another traumatic event for the tissues which reduces the likelihood for future problems. 

Till the next blog, stay active and stay well!

Lonan Hughes

Chartered Physiotherapist