Summary

This study demonstrated that the KL grade might be associated with meniscus extrusion, and the degree of meniscus extrusion was similar in knees with root tears and horizontal tears.

Abstract

Introduction

It is known that the meniscus extrusion causes hoop strain failure and increasing contact pressure is related to cartilage damage and osteoarthritis. However, it remains unclear whether extrusion precedes or follows osteoarthritic changes. The purpose of this study was to compare medial meniscus extrusion in normal knees and patients using ultrasonography (US), and to evaluate medial meniscus extrusion using US and Magnetic Resonance Imaging (MRI) in patients.

Materials And Methods

Thirty two patients (the patients group: mean age 58.8 years) with medial painful knees and twenty healthy volunteers (the control group: mean age 30.5 years) were included in this study. The OA stage was determined according to the Kellgren Lawrence (KL) grading. We used ultrasonography to measure the meniscus extrusion in volunteers and in patients with KL grade 0 (16 knees) and grade 1(16 knees). A single examiner performed US, with both knees in complete extension in 2 positions (supine and standing). Meniscus extrusion was measured as the distance from the edge of the medial meniscus to the tibial cortices.
In addition, all 32 cases in the patients group underwent MRI examination. Radiologists evaluated the pathological meniscus such as root tear and horizontal tear.

Results

In the control group, the mean meniscal extrusion was 1.0 ± 0.1mm without weight bearing and 1.1 ± 0.4mm with weight bearing, there were no significant differences with or without weight bearing.
In the patients group, the mean meniscal extrusion was 1.8 ± 0.8mm without weight bearing and 2.2 ± 1.1mm with weight bearing, meniscus extrusion with weight bearing was significantly larger than without weight bearing. (P<0.05)
We compared control group with patients group (KL grade 0 and KL grade1), meniscus extrusion was significantly different between the control and KL grade 1 with or without weight bearing. (P<0.01)
The radiologists evaluated the pathological meniscus in 32 knees. MRI findings were no abnormality in 12 knees, root tear in 7 knees, horizontal tear in 13 knees. Meniscus extrusion of both root tear (2.8 ± 1.1mm) and horizontal tear (2.5 ± 1.1mm) was significantly larger than with no abnormality (1.4 ± 0.4mm).

Discussion

Some authors reported that meniscal extrusion was associated with joint effusion and primary OA. Wenger et al. reported that in OA case increasing varus malalignment caused high biomechanical stress and displacement of the medial meniscus. In normal knee joint, medial meniscus is tightly fixed to the coronary ligament in the medial tibial plateau. Hada et al. demonstrated that osteophytes might loosen the attachments to the coronary ligament and cause meniscus extrusion.
Lee reported that the degree of major extrusion was similar in knees with root tears and non-root tears. Our study also demonstrated meniscus root tear and horizontal tear influenced extrusion similarly.
In conclusion, meniscus extrusion was influenced by weight bearing in patients. The KL grade might be associated with meniscus extrusion, and the degree of meniscus extrusion was similar in knees with root tears and horizontal tears.