A spreading roots sign: Characteristic sign of the preliminary stage of medial meniscus posterior root tear on magnetic resonance imaging

Medial meniscus posterior root tears (MMPRTs) can result in the development of osteoarthritis or osteonecrosis. Clinical experience suggests that symptoms such as dull pain or discomfort in the popliteal area or the calf area, which are sometimes misdiagnosed as sciatic nerve pain, may precede impending rupture. We found that bone marrow edema emanating from the meniscal root on magnetic resonance imaging (MRI) scans—spreading roots sign—may indicate the preliminary stage of an MMPRT. The purpose of this study was to evaluate the efficacy of the spreading roots sign as an MMPRT-predictor. In a retrospective study, we reviewed the chart data and MRI results of patients who had required surgery for an acute MMPRT. We grouped patients by whether or not they had reported the above-mentioned precursory symptoms prior to acute rupture (precursory symptom group/non-precursor group), and when possible, we examined MRI scans to identify with which events the appearance/disappearance of the spreading roots sign coincided. Sex, age, body mass index, bone mineral density, radiological parameters, and MRI parameters were compared between groups. Data from 24 patients (precursory symptom group, n = 17 [70.8 %]; non-precursor group, n = 7 [29.2 %]) were included; data from 5 patients included MRI scans prior to acute rupture. There were no significant differences between precursory symptom and non-precursor groups, except for the ratio of the presence of the spreading roots sign (p = 0.005). The appearance of the spreading roots sign on MRI scans coincided with the onset of precursory symptoms, and its disappearance coincided with acute rupture and the appearance of other MRI signs typical of MMPRT (white meniscus/truncation/meniscal extrusion/giraffe neck signs). Our findings suggest that the spreading roots sign can be used as a unique precursory sign for MMPRT.