Summary

The spreading roots sign, which indicates bone marrow edema and resembles roots spreading out from the meniscal root, may be a magnetic resonance imaging sign characteristic of the preliminary stage of a developing medial meniscus posterior root tear.

Abstract

Background

Medial meniscus posterior root tears (MMPRTs) can result in the development of osteoarthritis. Therefore, to prevent progression to osteoarthritis, early diagnosis and early intervention of MMPRTs may be required. Once an MMPRT is suspected, magnetic resonance imaging (MRI) permits accurate early diagnosis by using some typical signs (truncation, giraffe neck, white meniscus signs and meniscal extrusion). 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 MMPRT. However, there has been no report on MRI findings as precursor indicators of the development of an MMPRT.

Purpose

We found that bone marrow edema emanating from the meniscal root on MRI scans, i.e., spreading roots sign (SRS) may indicate the preliminary stage of an MMPRT. The purpose of this study was to evaluate the efficacy of the SRS as an MMPRT-predictor.

Methods

In a retrospective study, we reviewed the chart data and MRI results of patients who had required surgery for an acute-onset MMPRT between January 2018 and December 2020. Acute onsets were defined as those for which a date of onset could be specified. Surgical intervention had been indicated with osteoarthritis or progressive cartilage defect. Surgical treatments consisted of arthroscopic root repair with meniscal centralization and high tibial osteotomy (HTO) either alone or in combination and the use of HTO. 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 SRS coincided. Sex, age, body mass index, bone mineral density, radiological parameters, and MRI signs mentioned above were compared between groups. The weight-bearing line ratio and mechanical medial proximal tibial angle were calculated from full-length anteroposterior weight-bearing radiographs of the leg. The posterior tibial slope was measured on a lateral radiograph.

Results

Data from 24 patients (precursory symptom group, n=17 [70.8 %]; non-precursor group, n=7 [29.2 %]) were included; all patients had MRI scans just after acute MMPRT and 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 SRS (p=0.005). The appearance of the SRS 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 mentioned above. Conclusions: Our findings suggest that the SRS can be used as a unique precursory sign for MMPRT. The SRS may be a warning that an MMPRT is developing due to tensile stress of the meniscal hoop. The stress can be decreased by reducing the tension caused by the acute tear.