Time-Dependent Increase in Medial Meniscus Extrusion after Medial Meniscus Posterior Root Tear Analyzed by Using Magnetic Resonance Imaging
Yoshiki Okazaki, MD, Takayuki Furumatsu, MD, PhD, Yasunori Shimamura, MD, PhD, Kenta Saiga, MD, PhD, Hideki Ohashi, MD, Takahiko Uchino, MD, Yusuke Kamatsuki, MD, Yuki Okazaki, MD, and Toshifumi Ozaki, MD, PhD
Department of Orthopaedic Surgery, Okayama University Graduate School, Okayama, Japan
Correspondence to: Takayuki Furumatsu, MD, PhD
Department of Orthopaedic Surgery, Okayama University Graduate School, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan
Tel: +81-86-235-7273, Fax: +81-86-223-9727
E-mail: matino@md.okayama-u.ac.jp
Received: September 21, 2018; Revised: January 1, 2019; Accepted: February 7, 2019; Published online: March 18, 2019.
© Korean Knee Society. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Purpose: Medial meniscus posterior root tear (MMPRT) causes progression of medial meniscus extrusion (MME). This study aims to calculate the progression rate of MME based on findings in two preoperative magnetic resonance imaging (MRI) scans and determine the associated factors.
Materials and Methods: We retrospectively reviewed 33 patients (27 females and 6 males; mean age, 60 years) who underwent MRI twice, at a mean interval of 48 days. We measured the medial meniscus body width, medial joint space width (MJSW), and MME. The MME progression rate was derived from regression analysis of the increase in MME (ΔMME) between the two MRI scans. In addition, the correlations of the MME increase rate with age, body mass index, femorotibial angle, and MJSW were evaluated.
Results: The mean MME increased from 3.4 mm to 4.5 mm (p<0.001). A good correlation was observed between ΔMME and the interval of MRI scans (R2=0.621), and the MME progression rate was 0.020 mm per day. A moderate correlation was observed between the MME increase rate and the MJSW (R2=0.432).
Conclusions: The MME progression rate was rapid in MMPRT and narrowing of the MJSW was associated with the progression of MME.
Level of Evidence: V, Cross-sectional study
Keywords: Medial meniscus, Root tear, Extrusion, Magnetic resonance imaging, Risk factors


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