Feasibility of MRI for the evaluation of interosseous ligament vertical segment via subtalar arthroscopy correlation: comparison of 2D and 3D MR images.

BACKGROUND: Interosseous ligament vertical segment (IOLV) and calcaneofibular ligament (CFL) have been reported to be important in stabilizing the subtalar joint. Unlike CFL, there is not much information regarding the comparison of MRI results with surgical evaluation of IOLV and the comparison between 2D and 3D MRI on IOLV evaluation. The feasibility of MRI in IOLV evaluation has yet to be reported. The purpose of this study was to evaluate the validity and reliability of MRI in IOLV tear detection via correlation with arthroscopic results. We also compared the diagnostic performance of 2D and 3D MR images. METHODS: In this retrospective study, 52 patients who underwent subtalar arthroscopy after ankle MRI were enrolled. Arthroscopic results confirmed IOLV tear in 25 cases and intact IOLV in 27 cases. Two radiologists independently evaluated the IOLV tears using only conventional 2D images, followed by isotropic 3D images, and comparison with arthroscopic results. RESULTS: Only the 2D sequences interpreted by two readers showed a sensitivity of 64.0-96.0%, a specificity of 29.6-44.4%, a positive predictive value of 51.6-56.4%, and a negative predictive value of 57.1-88.9%. Addition of isotropic 3D sequences changed the sensitivity to 60.0-80.0%, specificity to 63.0-77.8%, positive predictive value to 64.3-76.9%, and negative predictive value to 66.7-80.8%. The overall diagnostic performance of isotropic 3D sequences (AUC values: 0.679-0.816) was higher than that of 2D sequences (AUC values: 0.568-0.647). Inter-observer and intra-observer agreement between the two readers was moderate-to-good for both 2D and 3D sequences. The diagnostic accuracy in 19 patients with tarsal sinus fat obliteration tended to increase from 26.3-42.1% to 57.9-73.7% with isotropic 3D sequences compared with 2D sequences. CONCLUSIONS: Isotropic 3D MRI was feasible for the assessment of IOLV tear prior to subtalar arthroscopy. Additional 3D sequences showed higher diagnostic accuracy compared with conventional 2D sequences in IOLV evaluation. Isotropic 3D sequences may be more valuable in detecting IOLV tear in case of tarsal sinus fat obliteration.