High validity of measuring the width and volume of medial meniscal extrusion three‐dimensionally using an MRI‐derived tibial model

Background Medial meniscal extrusion (MME) is an important marker of knee osteoarthritis (KOA) progression. The purposes of this study were: 1) to determine whether there are morphological differences between CT‐ and MRI‐derived tibial plateau models; and 2) to determine whether measurement of MME volume and width using an MRI‐derived tibial model is as accurate as measurements on a CT‐derived tibial model. Methods This was a cross‐sectional study that enrolled ten participants with medial KOA (Kellgren‐Lawrence grade 1 to 3). Primary outcome was surface difference of the medial tibial plateau between CT‐ and MRI‐derived models. Furthermore, volume and cross‐sectional area of the medial tibial plateau were compared between CT‐ and MRI‐derived models. Measurements of MME volume and width were compared between CT‐ and MRI‐derived tibial models. Results Minimal and maximal surface differences of the medial tibial plateau between the CT‐ and MRI‐derived models were − 0.15 [− 0.44, 0.14] mm (mean [95% confidence interval]) and 0.24 [− 0.09, 0.57] mm, respectively. There were no significant differences in volume and cross‐sectional area of the medial tibial plateau between CT‐ and MRI‐derived tibial models. The MME volumes measured on CT‐ and MRI‐derived models were 942.6 [597.7, 1287.6] mm 3 and 916.2 [557.9, 1274.6] mm 3 , respectively ( p  = 0.938). The MME widths measured on CT‐ and MRI‐derived models were 4.2 [1.9, 6.5] mm and 4.5 [2.2, 6.9] mm, respectively ( p  = 0.967). Conclusions CT‐ and MRI‐derived models of the medial tibial plateau did not show significant morphological differences. Both CT‐ and MRI‐derived tibia can be used as a reference to measure MME in early‐to‐moderate medial KOA.