The Anterolateral Ligament Has Limited Intrinsic Healing Potential: A Serial, 3-Dimensional-Magnetic Resonance Imaging Study of Anterior Cruciate Ligament-Injured Knees From the SANTI Study Group

Am J Sports Med. 2021 Jul;49(8):2125-2135. doi: 10.1177/03635465211013015. Epub 2021 May 20.


Background: Recent imaging studies demonstrate that the anterolateral ligament (ALL) is frequently injured at the time of anterior cruciate ligament (ACL) rupture. The intrinsic healing potential of these injuries after ACL reconstruction (ACLR) has not been defined.

Purpose/hypothesis: The primary objective was to evaluate the rate and duration of the healing process of injured ALLs after ACLR using serial 3-dimensional magnetic resonance imaging (3D-MRI). The secondary objective was to investigate whether any patient, injury, or surgical factors influenced the healing rate. The hypothesis was that serial imaging would demonstrate that the ALL has limited healing potential.

Study design: Case series; Level of evidence, 4.

Methods: Patients enrolled in the study underwent 3D-MRI (slice thickness 0.5 mm) preoperatively and at 1, 6, 12, and 24 months after ACLR. Three observers determined the grade of ALL injury according to the Muramatsu classification. Inter- and intraobserver reliabilities were calculated. The rates of injury and time points for healing were determined. Full healing was defined as a change from a preoperative Muramatsu grade of B or C (indicating partial or complete injury) to grade A (normal). Multivariate analysis was used to investigate the association of aforementioned factors with the risk of incomplete healing.

Results: A total of 44 patients were enrolled in the study. Of them, 71.2% had an ALL injury on preoperative imaging. Overall, full healing of ALL injuries occurred at a rate of 3.2%, 15.2%, and 30.3% at 1, 6, and 12 months, respectively. There were no changes in the Muramatsu grade in any patient beyond 12 months postoperatively. None of the complete lesions demonstrated full healing, but the proportion of patients with a grade C injury decreased from 13.6% preoperatively to 4.5% at 12 months due to an improvement to grade B in 4 of 6 patients (66%). Inter- and intraobserver reliabilities of the classification system were almost perfect at 0.81-0.94 and 0.95-1.00, respectively. None of the potential risk factors investigated were predictive of an increased risk of nonhealing.

Conclusion: ALL injuries occurred in the majority of ACL-injured knees. They had limited intrinsic healing potential, with only 30.3% healing by 12 months after ACLR. The process of healing took >6 months in half of the patients in whom it occurred. No new cases of full healing occurred beyond 12 months postoperatively. No significant risk factors for failure of full healing to occur were identified, but it is likely that this aspect of the study was underpowered.

Keywords: 3-dimensional magnetic resonance imaging; anterior cruciate ligament; anterolateral ligament.

MeSH terms

  • Anterior Cruciate Ligament / diagnostic imaging
  • Anterior Cruciate Ligament / surgery
  • Anterior Cruciate Ligament Injuries* / diagnostic imaging
  • Anterior Cruciate Ligament Injuries* / surgery
  • Anterior Cruciate Ligament Reconstruction*
  • Humans
  • Knee Joint / surgery
  • Magnetic Resonance Imaging