Description
【Objective】 Recently, there has been a growing interest in medial meniscal extrusion (MME) due to its reported association as a risk factor for the onset and progression of knee osteoarthritis (OA). MRI is the standard for the diagnosis of MME, but MRI has the disadvantage of being time consuming and expensive. Although simple X-ray is recommended as the initial examination for patients with knee pain, there are few reports evaluating medial meniscus extrusion on X-ray. In this study, we investigated the usefulness of MME detection using gradation processing of X-rays.
【Methods】
Patients aged 40 years or older who presented with knee pain between April 2020 and April 2022 and underwent simple X-ray and MRI imaging within 1 month were included. Trauma, tumor, and Kellgren-Lawrence (KL) grade IV cases were excluded. The amount of medial meniscus extrusion from the medial edze of the tibia (X-AMME) and the thickness of the meniscus (X-TMM) were investigated using gradely processed plain X-ray images. We also used the meniscal extrusion ratio (X-MMER), obtained by dividing the meniscal extrusion amount by the meniscal thickness.In addition, the amount of medial meniscal extrusion (M-AMME) was measured by MRI. Then, We evaluated the correlation between X-ray medial meniscal extrusion ratio (X-MMER) and MRI meniscal extrusion amount (M-AMME) using Pearson's correlation coefficient. We defined meniscal extrusion positivity as an extrusion of 3mm or more on MRI images and created a receiver operating characteristic (ROC) curve for the relationship between X-ray meniscal extrusion ratio (X-MMER) and meniscal extrusion positivity, determining the cutoff value of X-MMER for MRI meniscal extrusion positivity.
【Results】 A total of 57 knees were included, with 15 male and 42 female knees, an average age of 72 years, and KL grades of I: 30 knees, II: 18 knees, and III: 9 knees. A strong correlation was observed between the X-ray medial meniscal extrusion ratio (X-MMER) and the amount of MRI medial meniscal extrusion (M-AMME) (correlation coefficient 0.860, P＜0.0001). The cutoff value of X-MMER for MRI meniscal extrusion positivity was 0.50, with an AUC of 0.9825, Sensitivity: 0.9063, and Specificity: 0.8663.
【Conclusion】 From the present study, it was possible to measure the amount of meniscal extrusion and the thickness of the meniscus by gradation processing with X-rays without MRI, and to calculate the medial meniscal extrusion ratio (X-MMER), which strongly correlates with the amount of meniscal deviation on MRI (M-AMME). Setting the cutoff value for X-ray meniscal extrusion ratio at 0.50 could be useful for estimating the cause of knee pain, determining the need for additional MRI, and assessing the necessity of arthroscopic examination.
