It is commonly thought among surgeons and PTs that the ACL is not able to ever heal enough to restore knee stability. Based on everything I had read on rabbit studies, clinical experience and what was taught to me, I truly believed that once torn, the ACL could never just spontaneously heal. After all, the ACL has a unique anatomy and poor blood supply which made it “impossible” to heal once ruptured. Well I’m here to tell you that I was wrong in my belief!

This relatively small study involved 14 athletic patients post-acute complete ACL ruptures, as confirmed with positive Lachman and pivot shift tests and an MRI of course. Although clinically, all these individuals were indicated for ACL reconstruction surgery, each had chosen to postpone surgery for various reasons.

Amazingly, after 2 years, all 14 of the patients in this sample, presented with stable knees based on examination and… “In all patients, MRI at the time of follow-up showed an end-to-end continuous ACL with homogeneous signal and disappearance of the secondary signs”Costa Paz et al 20212

In one of the patients, who eventually needed a lateral meniscus repair, their spontaneous ACL healing was even confirmed arthroscopically.

Amazingly within the 2 years of the study, all 14 returned to their pre-injury activities and sports. Interestingly, after the study period, two of them had a re-injury and subsequently underwent an ACL reconstruction.

At this moment, we are unable to predict which patients have some healing potential of their ACL; perhaps it is in those who have a few fibers in continuity that were simply not visible on their original MRIs. Perhaps if there a strand of ACL left, scar tissue and healing can occur bridging the 2 ends.

“An important finding of the past decade is that the ACL is able to heal and subsequently restabilize the knee.”  Heusdens C 2021

Reference: Heusdens CHW. ACL Repair: A Game Changer or Will History Repeat Itself? A Critical Appraisal. J Clin Med. 2021 Feb 26;10(5):912.
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