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

Key points

1. 0153% of patients managed with rehabilitation alone had MRI evidence of ACL healing at 2 years; 58% at 5 years
2. 02Healed group had substantially better KOOS sport/recreation and quality-of-life scores at 2 years than non-healed, delayed surgery, and early surgery groups
3. 0363-94% of those with MRI-confirmed healing met the patient acceptable symptom state threshold across all KOOS subscales; none met treatment failure criteria
4. 04Signs of healing were visible on MRI as early as 3 months after injury
5. 05Knee laxity results were mixed: more normal pivot-shift tests in the healed group than non-healed, but fewer normal Lachman tests than surgically reconstructed groups

How it was conducted

Design

Secondary analysis of the KANON randomised controlled trial

Participants

120 young adults (aged 18-35) with acute ACL rupture within 4 weeks, randomised to early ACL reconstruction plus rehabilitation, or rehabilitation with optional delayed reconstruction

ACL healing assessment

MRI using the Anterior Cruciate Ligament OsteoArthritis Score (ACLOAS); grades 0-2 (ligament continuous) classified as healed, grade 3 (absent/discontinuous) as non-healed

Primary outcomes

KOOS sport and recreational function (KOOS-Sport/Rec) and KOOS quality of life (KOOS-QOL) at 2 and 5 years

Follow-up

2 years and 5 years

Analysis

Linear mixed models adjusted for age, sex, and smoking

What they found

• MRI evidence of ACL healing at 2 years: 16/54 (30%, 95% CI 19-43%) of all participants randomised to optional delayed reconstruction; 16/30 (53%, 95% CI 36-70%) among those managed with rehabilitation alone
• MRI evidence of ACL healing at 5 years: 58% (95% CI 39-76%) of participants managed with rehabilitation alone (n=24)
• Adjusted mean difference in KOOS-Sport/Rec at 2 years: healed vs non-healed 25.1 (95% CI 8.6 to 41.5); healed vs delayed ACLR 24.9 (95% CI 10.2 to 39.6); healed vs early ACLR 17.4 (95% CI 4.1 to 30.7)
• Adjusted mean difference in KOOS-QOL at 2 years: healed vs non-healed 27.5 (95% CI 13.2 to 41.8); healed vs delayed ACLR 18.1 (95% CI 5.4 to 30.8); healed vs early ACLR 11.4 (95% CI 0.0 to 22.9)
• Adjusted mean difference in KOOS-QOL at 5 years: healed vs non-healed 25.3 (95% CI 9.4 to 41.2); healed vs delayed ACLR -7.9 (95% CI -20.5 to 4.7); healed vs early ACLR -7.1 (95% CI -19.1 to 4.9)
• PASS criteria met at 2 years: 63-94% of healed group vs 29-61% in non-healed or reconstructed groups
• Treatment failure criteria met at 2 years: 0% in healed group vs 5-21% in other groups
• Normal/nearly normal pivot-shift test at 2 years: 75% healed, 46% non-healed, 92% delayed ACLR, 100% early ACLR
• Normal/nearly normal Lachman test at 2 years: 44% healed, 31% non-healed, 83% delayed ACLR, 93% early ACLR
• 3/15 participants who later had delayed ACLR showed MRI evidence of healing before crossing over to surgery
• Only 4/12 (33%) participants who did not cross over to surgery had a complete rupture on 3-month MRI, vs 13/14 (93%) who later had delayed surgery

Limitations

• Small subgroup sizes after stratification limit statistical power; 95% CIs were wide and guided interpretation rather than point estimates
• Secondary and exploratory analysis - not a pre-specified primary aim of the KANON trial
• Assessors were not blinded to treatment group for the pivot-shift test, introducing potential laxity measurement bias
• Findings are not generalisable to professional athletes or people with low pre-injury activity levels, both of whom were excluded

Why it matters

For patients

If you have torn your ACL, rehabilitation alone may allow the ligament to heal naturally in roughly one in two cases, with better knee function and quality of life than surgery in those who do heal.

For clinicians

MRI-confirmed ACL healing after a rehabilitation period is associated with markedly better patient-reported outcomes at 2 years, suggesting healing status could inform shared decision-making about whether to proceed with reconstruction.

For readers

This secondary analysis from the KANON RCT challenges the longstanding assumption that a ruptured ACL cannot heal, and provides the first quantitative outcome data linking MRI-confirmed healing to patient-reported benefit.