Picture archiving and communication system

The patients underwent open MRI evaluations using the Oasis 1. ,2). If osteophytes were present in the medial tibial plateau, they were excluded in the determination of the tibial margin as previously described [4] (link).
After assessing all coronal slices of each knee, measurements were taken from the 'most posterior' and 'second-most posterior' slices to obtain a high positive predictive value [2, (link)21] . The signal intensity of the MM posterior segment was compared to that of the 2 middle segment slices of the intact lateral meniscus (LM) on the ipsilateral side. The IMSI of the MM posterior segment was measured using a free-line region-of-interest (ROI) tool in a picture archiving and communication system (FUJIFILM Holdings Corporation, Tokyo, Japan). The ROI was marked by drawing a freehand line along the edge of the MM posterior segment. Because the IMSI can vary between examinations due to an inconsistent degree of screen contrast, the IMSI value was expressed as a ratio of the signal intensity of the MM posterior segment to that of the intact LM middle segments, as a control to standardize the signal intensity [22] . Preoperative IMSI values in each group defined the baseline as 1.

We used a picture archiving and communication system (FUJIFILM Holdings Corporation, Tokyo, Japan) to measure the Kellgren-Lawrence grade and FTA on the preoperative anteroposterior and lateral radiographs. Magnetic resonance imaging (MRI) of the knee was performed preoperatively and at the 1-year follow-up using the Achieva 1.5 T system (Philips, Amsterdam, Netherlands) under non-weight-bearing standardized conditions, as described previously [14] . The MRI-based medial meniscus body width (MMBW) was defined as the distance from the inner boundary to the outer boundary on a line passing through the anterior and posterior midpoint of the medial meniscus on a coronal slice. The absolute medial meniscus extrusion (aMME) was measured between the most medial margin of the meniscus and the most medial aspect of the tibia. The relative MME (rMME) was calculated using the following formula: 100 × aMME / MMBW (%) [5] .
The MMBW, aMME, and rMME were calculated preoperatively and at the 1-year follow-up. Two orthopedic surgeons performed each measurement twice with a 2-week interval between measurements in a blinded manner. Intra-and interobserver reliability for MMBW and MME were 0.93/0.89 and 0.92/0.88, respectively.