Gutierrez-Nibeyro SD, Werpy NM, White Ii NA, et al.
High- and low-field magnetic resonance (MR) imaging systems are available for clinical diagnosis of collateral desmopathy of the equine distal interphalangeal joint (DIJ). Knowledge of the normal appearance, size, shape, and signal variation of these ligaments on high- and low-field MR images is essential when assessing desmopathy detected by MR imaging. However, there are no descriptions of the normal features of DIJ collateral ligaments on images obtained with a standing low-field MR system. Low-field MR imaging characteristics of normal collateral ligaments of the DIJ of cadaver feet were corroborated with high-field MR imaging and histologic examination to exclude desmopathy. The size and shape of the collateral ligaments of the DIJ was similar among limbs; however, the signal pattern of the ligaments varied depending on the segment of the ligament being assessed and the MR sequence used. In limbs positioned within the magnet as recommended for clinical MR imaging, collateral ligaments of the DIJ have heterogeneous signal pattern with a peripheral region of increased signal intensity at the level of the middle phalanx that can be confused with a desmopathy. The MR imaging characteristics of normal collateral ligaments of the DIJ are related to their anatomy and fiber configuration. The results of this study support the presence of magic angle effect within the axial margin of the CL of the DIJ at the level of fiber divergence within the proximal to mid-portion of the ligament.