DETERMINATION OF CARTILAGE THICKNESS IN T HE ANKLE JOINT - MRT (1.5T)COMPARATIVE ANATOMICAL STUDY

Purpose: The aim of this study was to evaluate the accuracy of MRI in the measurement of cartilage thickness of the ankle joint in compariso n to pathologic and histologic specimens. Patients and methods: The an kle joints of four fresh cadaver feet were imaged on a 1.5 T MR-unit i n the coronal plane. Standard T-1-weighted spin echo (SE) and a T-1-we ighted 3D-GE (FLASH-3D) sequence with fat saturation were applied. Fol lowing MR imaging, the talus was explanted and cut parallel to the MR images for macroscopic evaluation and histologic specimens were prepar ed. MRI measurements of the cartilage thickness of the talus were carr ied out in two ways: without and with consideration of a transition zo ne of intermediate signal intensity between hyperintense cartilage and hypointense cortical bone. The data were compared with the anatomic s pecimens as the gold standard expressing the difference as a percentag e value. On histologic specimens thickness of deep calcified cartilage layer was measured. Results: Measurements without the transition zone showed a mean underestimation of talus cartilage thickness of 46.8% ( 41.3 - 52.1) for T-1-SE and 47.5% (43.1 - 52.1) for fat saturated FLAS H-3D images. Considering the transition zone the mean values were 25.0 % (23.1 - 26.2) and 14.1% (6.7 - 21.5). The histologic specimens showe d a three-fold increase of thickness of deep calcified cartilage layer . Conclusions: Measurements of the cartilage layer of the ankle joint on MR images are only accurate if the transition zone (calcified carti lage layer) is considered and the optimal pulse sequence (FLASH-3D-fat -sat) is applied.