Trinity, 3-year-old Quarter Horse mare, presented to Animal Imaging for magnetic resonance imaging of the right hind limb. She had an acute onset grade 2/5 right hind limb lameness that resolves with diagnostic anesthesia of a low-4 point nerve block. Repeated treatment of the right hind fetlock joint with intraarticular therapy and shockwave did not change the lameness. The referring veterinarian collected an initial full series of radiographs of which 3 images are shown here.
As you can see on the collected radiographs, the midsagittal ridge of the distal metatarsal bone (blue arrow) has a small area of lucency. This sparked concern for the referring veterinarian when paired with the lack of response to initiated therapy. Ultimately, the owner agreed to pursue magnetic resonance imaging (MRI) to better understand the health of the bone and cartilage of this area. MRI images of the right hind fetlock were collected and are shown below.
In this first set of images, the MRI scan performed was that of a STIR (short tau inversion recovery). When STIR sequences are used for musculoskeletal imaging in horses, images are generated so that bone appears black and fluid appears white. This allows for sensitive
detection of areas of bone that may have edema, or fluid, within them. This is commonly thought of as a bone bruise. As you can see on the transverse image provided (image left). The bone has a sharp distinction between a white and a black aspect. This is indicative of bone edema. The image on the right is provided to help orient with the location of the transverse slice show as shown with the green line through the bone.
Furthermore, the additional provided dorsal image shows a mild subchondral bone defect of the midsagittal ridge as seen on initial radiographs. MRI allowed for complete evaluation of the remaining cartilage of this joint, ultimately finding minimal cartilage damage and thereby improving the overall prognosis for this horse as an athlete. Rest is the best treatment for bone injury in horses, therefore allowed the client and veterinarian to make the most informed decision on the recommended rehabilitation for this horse.
