HIGH FIELD MAGNETIC RESONANCE AND MULTIDETECTOR COMPUTED TOMOGRAPHY OF THE NORMAL CANINE STIFLE UNDER VARYING FLEXION ANGLES

Several new imaging modalities have been described for the evaluation of the canine stifle. However, to our knowledge, imaging of the stifle at varying degree of flexion has not been investigated. Our purpose was to compare high field magnetic resonance (MRI) and computed tomography (CT) of the normal stifle at varying flexion angles to describe and evaluate the visualization of its structures when positioned in four different flexion angles (85°-110°-135°-160°). Six canine hind limbs were imaged at four different flexion angles using a 1.5 Tesla commercial MR unit and a multi-slices CT scanner. For each CT and MRI scan two board certified veterinary radiologists independently evaluated the cranial and the caudal cruciate ligament, the medial and the lateral meniscus, the femoral and tibial cartilage, using a visual assessment score of 0-3 and subjective criteria previously described by Podadera et al. A score of 0 indicated that the structure was not visible. A score of 1 indicated that the structure was visualized partially. A score of 2 indicated that the totality of the structure was identified but poorly demarcated. A score of 3 indicated that the structure was totally visualized and well demarcated. Statistical analysis was performed to evaluate the intermodality difference and the interobserver difference, the effect of each flexion angle and the effect of the plane on the visualization score of the different structures. The visualization scores obtained for MRI were statistically significant different compared to those obtained with CT images. There was statistically significant difference between the two observers. From the pairwise comparison of the different flexion angles the 85° and 110° degree of flexion resulted to be the best angles to visualize all the structures. All of the joint structure of the canine stifle can be better identified and evaluated by MRI. Most of the soft tissue structures that were seen on MRI were also identified on CT images using a soft tissue window, but never with the definition that MRI offers. Imaging of the stifle in flexion conditions resulted in better visualization and delineation of the main stile joint structures, with particular focus on the cruciate ligaments and the menisci.