Abstract
Objectives:
Anterior instability (AI) of the lateral meniscus is potentially debilitating in young patients. The lack of reliable and accurate Magnetic Resonance Imaging (MRI) findings limits the ability to preoperatively recognize AI. The goal of this study is to present a novel MRI finding (phantom sign) for AI of the lateral meniscus.
Methods:
Two independent blinded reviewers performed retrospective review of preoperative MRI for all patients who underwent lateral meniscus repair between 7/1/2019 and 3/31/2022 by a single fellowship trained surgeon. Positive phantom sign was defined as attenuated or decreased signal intensity along the anterior horn of the lateral meniscus on a single coronal cut at the anterior tibial insertion of the ACL. The lateral meniscus was also evaluated on coronal MRI for lateral extrusion, posterior displacement and posterior “megahorn” on sagittal cuts, and increased fluid signal adjacent to the anterior horn or a radial tear at the anterior root on axial cuts. Intraclass Pearson correlations were calculated for inter and intra-rater reliability in assessment for presence of pathology on MRI. Predictive ability of each imaging finding with at least good (ICC 0.6 or above) reliability was also evaluated by comparing MRI and documented intraoperative findings.
Results:
55 patients with preoperative MRIs of arthroscopically repaired lateral meniscus tears were included. 21 patients (38.2%) were female with median age 15.0 years (range 10.5-16.0). 26 patients (47.3%) had a discoid lateral meniscus (DLM). Lateral meniscus AI was present on arthroscopy for 25 knees (45.5%) and among these 18 had concurrent DLM. Intraclass correlation was good for phantom sign (ICC 0.75, 95% CI 0.60-0.84), lateral extrusion (ICC 0.60 95% CI 0.41-0.75), posterior displacement (ICC 0.71, 95% CI 0.55-0.82), and posterior “megahorn” (ICC 0.76, 95% CI 0.62-0.85). On predictive analysis, phantom sign was 95.0% sensitive and 74.2% specific for lateral meniscal anterior instability. Posterior displacement and posterior megahorn were specific for anterior instability (both 93.3%) though with limited sensitivity (32.0% and 28.6%, respectively).
Conclusions:
Phantom sign is a reliable and sensitive MRI finding for AI, even in the absence of frank displacement of the meniscus, and should prompt thorough arthroscopic evaluation for this pathology. It may help guide treatment decision-making and preoperative planning, which may in turn improve patient outcomes and reduce complications of untreated anterior instability.
