Introduction

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 following ACL reconstruction (ACLR) has not been defined. The primary objective of this study was to evaluate the rate and duration of the healing process of injured ALLs following ACLR, by serial three-dimensional magnetic resonance imaging (3D-MRI). The secondary objective was to investigate whether any patient, injury or surgical factors significantly influenced the healing rate. The hypothesis was that serial imaging would demonstrate that the anterolateral ligament has limited intrinsic healing potential.

Methods

Patients enrolled to the study underwent 3D-MRI evaluation pre-operatively and at 1,6,12 and 24 months following ACL reconstruction. Three independent observers determined the grade of ALL injury according to the Muramatsu classification (Type A: ALL visualized as a continuous, clearly defined low signal band. Type B: ALL exhibits warping, thinning or iso-signal changes, Type C: Absence of clear continuity of ALL). Inter- and intra-observer reliabilities were calculated. The rates of injury and time-points for healing were determined. Full healing was defined as a change from a pre-operative Muramatsu grade of B or C, to grade A. Multivariate analysis was performed in order to investigate the association of patient, injury and surgical factors with the risk of incomplete healing.

Results

Forty-four patients were enrolled to the study. A mean of 71.2% had an ALL injury on pre-operative imaging. Overall, full healing of ALL injuries occurred at a rate of 3%, 15.2%, 30.3% and 30.3% at 1, 6, 12 and 24 months respectively. None of the complete lesions of the ALL demonstrated full healing. The inter- and intra-observer reliabilities of the classification system were almost perfect at 0.81-0.94 and 0.95-1, respectively. None of the demographic, injury or surgical factors investigated were predictive of an increased risk of non-healing.

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 following ACL reconstruction. The process of healing took longer than six months in 50% of patients. No new cases of full healing occurred beyond 12 months post-operatively. No significant risk factors for failure of full healing to occur were identified.