Summary
Do not rely on MRI evidence of anterolateral capsule injury alone as an indicator for Lateral Extra-articular Tenodesis in the setting of acute ACL injury evidence of anterolateral complex injury in the setting of ACL injury
Abstract
Background
The natural history of Kaplan Fiber (KF) injury following acute primary anterior cruciate ligament (ACL) reconstruction (ACLR) remains unknown.
Purpose/hypothesis: To evaluate the temporal change in MRI appearance of the KF complex following acute primary ACLR. It was hypothesised that KF injury would resolve with time.
Study Design: Cohort study; Level of evidence, 3
Methods
A retrospective magnetic resonance imaging (MRI) analysis was conducted on 89 patients with ACL-injured knees to assess the change in radiological appearance of the KF following primary ACLR. Patients who had an index MRI and ACLR within 90 days of injury, and a further MRI at 9-months following surgery, were included. Diagnostic criteria to identify radiological evidence of KF injury and subsequent resolution were applied, including the presence of high signal intensity on fluid sensitive sequences, which is indicative of a pathological process radiologically. The proximity of the KF to the femoral Endo-Button (EB) was noted on MRI and quantified in millimetres (mm).
Results
KF injury was identified in 30.0% (27/89) of patients with isolated high signal observed in an additional 17.8% (16/89). At 9-months, MRI evidence of reconstitution of the KF complex was found in 51.9% of patients (14/27) with persistent discontinuity in the remaining patients (13/27). All patients (16/16) with isolated high signal had complete resolution on repeat MRI. KF thickening was observed in 26% (12/46) of patients with a previously normal KF and in 25% (4/16) with isolated high-signal. The EB was positioned in close proximity (<6mm) to the centre of the KF attachment in 62% (55/89) of cases and this was associated with increased rates of KF thickening.
Conclusion
KF injury resolved radiologically in over half of the patients at 9-months following acute primary ACLR. High signal in the region of the KF on the index MRI resolved in all cases with evidence of residual KF thickening in only 25% of cases at repeat MRI, equivalent to the rate of KF-intact knees. As such, it is not advisable to use high signal on preoperative MRI as the sole criterion for the diagnosis of KF injury. The position of the EB following ACLR is intimately related to the KF attachment in the majority of patients. This can be associated with KF thickening on postoperative MRIs.