Summary

Medial meniscus extrusion is significantly greater in degenerative meniscus tears case compared to no degenerative tears case, with the anterior and posterior horns shifting posteriorly and anteriorly, respectively, highlighting the dynamic positional changes of the meniscus associated with degenerative tears.

Abstract

Introduction

Medial meniscus extrusion (MME) frequently occurs in conjunction with medial meniscus tears. Medial meniscus tears lead to dysfunction in stress distribution and progressive MME with increasing contact pressure in certain areas. Although the anterior and posterior roots of the medial meniscus are fixed, the positions of the anterior and posterior angles are expected to change with MME, however, this correlation remains unclear. In vitro studies suggest that reduced motion of the posterior horn of the medial meniscus is a potential mechanism for meniscal tears, causing the fibrocartilage to be “trapped” between the femoral condyle and tibial plateau during full flexion. Degenerative tears of the posterior segment of medial meniscus often show the posterior horn anteriorly on arthroscopy. This study aimed to determine the position of the medial meniscus in patients with medial knee pain and a Kellgren–Lawrence (KL) grade ≤1, which is not included in the general definition of osteoarthritis (OA). We hypothesized that MME would be greater in cases of degenerative tears and that the anterior and posterior horns would move posteriorly and anteriorly, respectively.

Materials And Methods

This non-randomized, prospective, multicenter clinical trial was approved by the ethics committee of our hospital. Patients with KL grade ≤1 and no history of ipsilateral lower-extremity surgery were recruited from those visiting with medial knee-joint pain. All patients underwent radiographic and magnetic resonance imaging (MRI) examinations, with 175 knees included in the study, excluding cases with posterior root tears of the medial meniscus. The KL grade and weight-bearing line ratio (WBLR) were determined using standing plain frontal radiographs and full-length radiographs, respectively. Patients with Mink grade 3 horizontal tears in the posterior segment of the medial meniscus on MRI were classified into the degenerative tear group (Group T), while the others were classified as having no degenerative tears (Group C). MME was defined as the greatest horizontal distance between the most medial aspects of the tibia and meniscus. The positions of the anterior and posterior horns were determined using specific landmarks on MRI. The ratios of the distances from the anterior edge (anterior-horn position) and posterior edge (posterior-horn position) to the tibial width were determined. Student's t-test and Pearson's χ2 test were performed to compare age, sex, KL grade, WBLR, MME, and the positions of the posterior point of the anterior horn and anterior point of the posterior horn between Groups T and C. Statistical significance was set at P< 0.05.

Results

A total of 175 patients were enrolled, with 102 in Group T and 73 in Group C. No significant differences in age, gender, and WBLR were found between the groups. In Group T, the anterior horn, medial segment, and posterior horn were shifted posteriorly (Group T: 17.1±5.0%; Group C: 14.8±4.1%; p<0.01), medially (Group T: 2.6±1.2 mm; Group C: 2.0±1.2 mm; p<0.01), and anteriorly (Group T: 36.6±6.4%; Group C: 27.8±6.1%; p<0.01), respectively.

Conclusions

MME was larger in degenerative meniscal tears than in cases without tears, with the anterior and posterior horns shifting posteriorly and anteriorly, respectively.