Risk factors for passive anterior tibial subluxation on MRI in complete ACL tear

Introduction: In anterior cruciate ligament (ACL) tear, passive spontaneous anterior tibial subluxation (ATS), with respect to the femur, is sometimes observed on MRI. In a case-control study, ATS >3.5 mm showed 100% specificity (= 3.6, 95% CI) for complete ACL tear. The aim of the present study was to assess the relation between ATS on MRI and associated lesions in complete ACL tear. The study hypothesis was that associated lesions are a risk factor for ATS. Material and methods: A retrospective study included patients operated on for complete ACL tear between 2010 and 2015. Exclusion criteria comprised associated posterior cruciate ligament tear, partial ACL tear, and history of knee surgery. Preoperative MRI was performed with the patient in supine position and the knee in 20 degrees flexion in neutral rotation. ATS was measured by axial superimposition of the bicondylar slice on the slice through the tibial plateau. Associated lesions were assessed: medial and lateral menisci, collateral ligaments, posteromedial and posterolateral corners, tibiofemoral compartment cartilage and cancellous bone. Factors associated with ATS > 3.5 mm were analyzed. Ninety-one patients were included: mean age, 31.1 +/- 10.1 years; 34 female, 57 male. Mean time from injury to MRI was 7.8 +/- 11.7 months (range, 0.7-60 months). Results: Mean ATS was 4.7 +/- 2.3 mm. Inter- and intra-observer reproducibility for ATS measurement were excellent. On preoperative MRI, 61.1% of patients showed bone edema, 48.4% medial meniscal tear, and 36.3% lateral meniscal tear. ATS was significantly greater in case of medial meniscal tear (5.4 +/- 2.3 mm vs. 4 = 2.1 mm; p = 0.003). No significant differences were found according to other lesions. Fifty-four patients (59.3%) showed ATS >3.5 mm; risk factors comprised medial meniscal tear (OR= 2.6, 95%CI [1.1-6.2]; p = 0.03) and injury-to-MRI time >9 months (OR = 9.8, 95% CI [1.1-85.2]; p = 0.04). Conclusion: Spontaneous anterior tibial subluxation on MRI in complete ACL tear was significantly associated with medial meniscal tear and accident-to-MRI time. (C) 2019 Elsevier Masson SAS. All rights reserved.