- There is exploratory evidence that there may be signs of anterior cruciate ligament (ACL) healing at 2 and 5 years after injury in those who opted for rehabilitation only in the KANON trial.
- Participants with evidence of ACL healing appeared to have better Knee Injury and Osteoarthritis Outcome Score at 2 years, but not 5 year follow ups, when compared to non-healed, early, or delayed ACL replacement groups.
- Spontaneous ACL healing may occur more frequently than previously thought.
BACKGROUND & OBJECTIVE
Can the anterior cruciate ligament (ACL) heal? This has been a looming question for centuries as we have seen different management and surgical procedures arise to optimize ACL healing and outcomes. The significant ramifications of potential ACL healing will not only reduce time-loss from sport and recreational activity but decrease the substantial burden these injuries have on the health system and patients.
This study explored the proportion of patients with evidence of ACL healing on MRI in the first 5 years after an ACL rupture and assessed the impact of ACL healing on functional outcomes.
This study continues to support the avoidance of early surgery unless necessary when treating anterior cruciate ligament tears.
This was a secondary analysis of the Knee Anterior Cruciate Ligament Nonsurgical vs Surgical Treatment (KANON) trial (1). Patients in the KANON randomized controlled trial (RCT) were aged 18-35 years with an acute ACL rupture confirmed on MRI within four weeks.
62 patients were randomized to early ACL reconstruction (ACLR) and 59 to rehabilitation with the option of delayed surgery. 51% of patients in the delayed group had ACLR within 5 years.
ACL healing was measured on MRI at two- and five-year follow-ups and defined using a grading system (see Table 1). Binary cut-off was used to group participants with scores of 0-2 (considered ‘evidence of healing’) and scores of 3 (considered as non-healed) on MRI.
Functional outcomes included the Knee Injury and Osteoarthritis Outcome Score (KOOS), osteoarthritis on x-rays, physical activity measured on the Tegner Activity Scale (TAS) and knee laxity on a Lachman test.
Data analysis included:
- Proportion of healed ACL on MRI for patients randomized to the rehabilitation and option of delayed surgery group
- Differences in functional outcomes assessed at two- and five-year follow-ups based on healing observed on MRI/treatment status
- Relationship between ACL healing/treatment status on functional outcomes at two- and five-year follow-ups.
At two-year follow-up, 16/54 (30%, 95% CI, 19-43) participants in the rehabilitation and optional delayed surgery group had evidence of ACL healing on MRI. However, 24 participants went on to have surgery. Of the 30 remaining in the rehabilitation only group, 16/30 (53%, 95% CI, 36-70) had evidence of ACL healing at two years. At five years, 16/28 (58%, 95% CI, 39-76) had evidence of ACL healing.
Participants with evidence of ACL healing reported better KOOS scores at two years over participants with non-healed ACL or those in the early or delayed ACLR groups. However, at five years, all groups had similar KOOS scores (See figure below). TAS scores were similar in all groups at two- and five-year follow-ups.
When assessing the relationship between ACL healing/treatment status on functional outcomes, participants in the healed group had better KOOS Sport and Recreation subscale at two years but not five years compared to other groups. At five years, KOOS-QOL scores were better in the healed group vs the non-healed group, however, scores appeared similar across the early and delayed ACLR at two- and five-year follow-up.
This study was a secondary analysis and was not powered (i.e. sufficient sample size) to answer the research question. The small sample size and wide confidence intervals indicates a lack of certainty in the conclusions and findings should be interpreted with caution.
This study was conducted in recreational athletes, and we are unable to generalize to elite athletes or patients in jobs that place high demand on their knees (e.g. firefighters).
While it is easier to conduct statistical analyses by dichotomizing or making binary groups (as in this case), these are arbitrary cut-offs. Clinically, a participant who scores a 0 on the MRI grading could be argued to be very different than a participant who scored 2, however, they are grouped in the ‘same’ group.
While this study provides exploratory evidence that the ACL can heal spontaneously, it by no means replaces our current knowledge and management of ACL tears. However, it does shed light on the fact that patients will benefit from a period of rehabilitation first before deciding upon surgical or non-surgical management, and perhaps one of these benefits is potential healing of the ACL. We still do not know who or what type of patients may lead to ACL healing and current trials are underway regarding bracing acute ACL tears to promote healing (2). Nonetheless, this study continues to support the need to avoid early surgery unless necessary (e.g. elite athletes who do not have the luxury of trialling a 6-month non-surgical option).
As stated across numerous conditions, imaging does not necessarily correlate with functional status and symptom presentation and should never be used to ‘treat, diagnose, or group’ patients (3). Although it is exciting to see some evidence of ACL healing, this must still correlate with the presentation of the patient and their current limitations. Until more research arises in this field, a shared decision-making approach should be considered best practice when helping patients determine the best management options for their ACL tear.
Filbay S, Roemer F, Lohmander L, Turkiewicz A, Roos E, Frobell R, Englund M (2022) Evidence of ACL healing on MRI following ACL rupture treated with rehabilitation alone may be associated with better patient-reported outcomes: a secondary analysis from the KANON trial. British Journal of Sport Medicine, 0,1-9.
- Frobell, R.B. et al. (2013) “Treatment for acute anterior cruciate ligament tear: Five year outcome of Randomised Trial,” BMJ, 346(jan24 1).
- Dr David Samra: Sports medicine sydney: ACL Bracing Protocol (no date) Dr David Samra, Sport and Exercise Medicine. (Accessed: December 12, 2022).
- Bedson, J. and Croft, P.R. (2008) “The discordance between clinical and radiographic knee osteoarthritis: A systematic search and summary of the literature,” BMC Musculoskeletal Disorders, 9(1).