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

Abstract

Objectives: Evaluate the natural course of anterior cruciate ligament (ACL) healing on MRI within 5 years of acute ACL rupture and compare 2-year and 5-year outcomes based on healing status and treatment group.

Methods: Secondary analysis of 120 Knee Anterior Cruciate Ligament Nonsurgical vs Surgical Treatment (KANON) trial participants randomised to rehabilitation and optional delayed ACL reconstruction (ACLR) or early ACLR and rehabilitation. ACL continuity on MRI (Anterior Cruciate Ligament OsteoArthritis Score 0-2) was considered evidence of ACL healing. Outcomes included Knee Injury and Osteoarthritis Outcome Score (KOOS), KOOS patient acceptable symptomatic state (PASS) and treatment failure criteria. Linear mixed models were used to estimate adjusted mean differences (95% CIs) in patient-reported sport and recreational function (KOOS-Sport/Rec) and quality of life (KOOS-QOL) at 2 and 5 years, between participants with MRI evidence of ACL healing and those who had (1) no evidence of ACL healing, (2) delayed ACLR or (3) early ACLR.

Results: MRI evidence of ACL healing at 2-year follow-up was observed in 16 of 54 (30%, 95% CI 19 to 43%) participants randomised to optional delayed ACLR. Excluding participants who had delayed ACLR, 16 of 30 (53%, 36-70%) participants managed with rehabilitation-alone displayed MRI evidence of ACL healing. Two-year outcomes were better in the healed ACL group (n=16) compared with the non-healed (n=14) (mean difference (95% CI) KOOS-Sport/Rec: 25.1 (8.6-41.5); KOOS-QOL: 27.5 (13.2-41.8)), delayed ACLR (n=24) (KOOS-Sport/Rec: 24.9 (10.2-39.6); KOOS-QOL: 18.1 (5.4-30.8)) and early ACLR (n=62) (KOOS-Sport/Rec: 17.4 (4.1-30.7); KOOS-QOL: 11.4 (0.0-22.9)) groups. Five-year KOOS-QOL was better in the healed versus non-healed group (25.3 (9.4-41.2)). Of participants with MRI evidence of ACL healing, 63-94% met the PASS criteria for each KOOS subscale, compared with 29-61% in the non-healed or reconstructed groups.

Conclusions: MRI appearance of ACL healing after ACL rupture occurred in one in three adults randomised to initial rehabilitation and one in two who did not cross-over to delayed ACLR and was associated with favourable outcomes. The potential for spontaneous healing of the ACL to facilitate better clinical outcomes may be greater than previously considered.

Trial registration number: ISRCTN84752559.

Keywords: Magnetic Resonance Imaging; anterior cruciate ligament; osteoarthritis; quality of life; rehabilitation.

Figure 1

Evidence of ACL healing on MRI over 5 years in a KANON study participant (male, aged 31 years at the time of injury) randomised to rehabilitation and optional delayed ACLR. (A) Baseline sagittal short tau inversion recovery (STIR) MRI shows complete disruption of the ACL, which is depicted as a hyperintense thickened structure (arrowhead). In addition, image depicts a characteristic traumatic bone marrow lesion (also referred to as bone contusion) in the posterior lateral tibia (arrow). (B) 3-month follow-up MRI shows complete resolution of bone contusion. There is beginning scar formation with partial hypointensity in the course of the ACL. Scar is still markedly thickened. (C) At 1 year, there is near-complete normalisation of scar formation with a re-ligamentisation and regular course. There is some remaining intraligamentous hyperintensity (arrowhead). (D) 2 years after the injury there is complete normalisation of structure and signal indicating healing of the ligament. (E) At 5 years persistent normalisation with regular ACL course and signal intensity is depicted (arrowheads). (F) Corresponding coronal STIR MRI at baseline confirms the disrupted hyperintense ACL near the proximal femoral attachment (arrowhead). There are large bone contusions at the medial and lateral tibia and lateral femur (arrowheads). (G) At 5 years, normalisation with a now hypointense healed ACL is shown also in the coronal STIR image. There is compete resolution of bone contusions. ACL, anterior cruciate ligament; ACLR, ACL reconstruction; KANON, Knee Anterior Cruciate Ligament Nonsurgical vs Surgical Treatment.

Figure 2

Mean KOOS subscale scores classified by treatment group and ACL healing status at 2 years. ACL, anterior cruciate ligament; ACLR, ACL reconstruction; KOOS, Knee Injury and Osteoarthritis Outcome Score; QOL, quality of life.

Figure 3

The percentage of participants meeting criteria for patient acceptable symptom state and treatment failure for each KOOS subscale at 2-year follow-up. Percentages do not add up to 100%, the missing percentage is explained by participants who scored above the criteria for treatment failure and below the criteria for patient acceptable symptomatic state for a given KOOS subscale. ACL, anterior cruciate ligament; ACLR, ACL reconstruction; KOOS, Knee Injury and Osteoarthritis Outcome Score; QOL, quality of life.