The high degree of detail seen with MRI has made it possible for veterinarians to find equine injuries they’ve never seen before. One example of this–MRI evaluation of desmitis in the oblique and straight distal sesamoidean ligaments–was discussed at the 2007 American Association of Equine Practitioners Convention, held Dec. 1-5 in Orlando, Fla. Sarah Sampson, DVM, doctoral graduate student in equine surgery and MRI at Washington State University (WSU), discussed the anatomy of these ligaments and a study of findings and treatment success in 27 horses.

"The distal sesamoidean ligaments include four ligaments (straight, paired oblique, paired cruciate, and paired short distal sesamoidean ligaments) that comprise the distal suspensory apparatus," she explained. "That apparatus resists extension of the fetlock and holds the suspensory bones to the first and second phalanges. The distal sesamoidean ligaments are susceptible to overload injury from hyperextension.

"Initially, diagnosis of desmitis in these ligaments relied on observations of swelling over the palmaroproximal (upper rear) aspect of the digit or on ruling out other causes of lameness in the area with radiographs," she noted. Ultrasound has been helpful in some cases, but she said this area is hard to evaluate with ultrasound.

However, MRI was found to be a very good way to identify these injuries, much more so than ultrasound or swelling. After describing the anatomy and imaging of these ligaments in great detail, Sampson described a retrospective study of affected horses. Of the 27 horses, most (15, 55.6%) were jumpers or dressage horses, and the age range of the whole group was 2 to 13 years. All were lame–six for less than four months, 19 for longer, and two for an unknown length of time. Seventeen horses had hind limb lameness (left, right, or bilateral), while the rest had forelimb lameness