Equine suspensory desmitis (Proceedings)
Equine suspensory desmitis is a common cause of lameness in the athletic equine, regardless of discipline. The condition seems to be different in the forelimb and hindlimb, so these will be discussed independently.
Forelimb suspensory desmitis, including proximal, body, and branch lesions can result in a very mild or subtle lameness or performance decrease, to a more severe lameness. When a lameness is present, it is often more evident on soft ground, and often more evident when the lame leg is on the outside of the circle. The lameness is best described as an advancing leg lameness, meaning the maximal head excursion is during the swing phase of the stride. The problem can affect one or both legs. When both legs are involved, a change in gait or gait quality is seen rather than a distinct lameness.
Horses with forelimb suspensory desmitis will have a variable response to forelimb flexion tests, but most often are positive to both distal limb and carpal flexions. I have found that horses with insertional lesions (either proximal or distal insertions) usually react very strongly to both of these flexions. Digital palpation is extremely important in evaluating forelimb suspensory ligament disorders. Normal horses should not be painful to palpation of the suspensory ligament. In addition to pain on palpation, I evaluate size differences in the branches or any enlargements in the body. In some horses, particularly those with subtle problems, palpable pain and a positive response to flexion are only seen after some degree of work. Often times the reaction to flexion tests will worsen at subsequent flexions.It is important to remember that there is rarely any external abnormality (swelling) with even the most severe form of suspensory desmitis. However, most branch lesions will have some enlargement or peri-ligamentous swelling, but this may only be able to be detected by digital palpation with the limb off of the ground. It is also important to remember that forelimb suspensory desmitis, while it can be the sole cause of the lameness, often can be present in combination with other sources of lameness, so a thorough lameness examination is always necessary.
With obvious forelimb suspensory desmitis, diagnostic anesthesia may not be necessary. However, one has to be certain that it is the sole cause of the lameness. Routine diagnostic anesthesia of the distal limb is usually employed to rule out lameness arising from below the fetlock. Low volar anesthesia will alleviate pain from the suspensory branches and body. A lateral palmar nerve block will alleviate most of the pain from the entire suspensory ligament; however, pain coming from the suspensory origin will only be variably blocked. In some horses, the palpable pain in the suspensory can be alleviated with diagnostic anesthesia, but not the clinical lameness. In these cases I will infiltrate the proximal suspensory with local anesthetic. This will usually alleviate lameness arising from the origin of the suspensory.
One must be careful with interpreting perineural nerve blocks above the palmar digital nerves. I have found that marked proximal diffusion of local anesthetics can occur from abaxial and low volar blocks, leading to false conclusions. Therefore, intra-articular blocks are generally used to help rule out fetlock and pastern problems rather than perineural nerve blocks.
Routine diagnostic imaging of the suspensory ligament includes ultrasound and radiology. When evaluating the suspensory ligament with the ultrasound, the entire ligament (origin, body, and branches) should be evaluated in both a transverse and longitudinal orientations. Thickness and cross sectional area of the structures should also be ascertained. A systematic approach should be used so that one becomes accustomed to what the normal appearance should be. Ultrasonographic abnormalities include changes in echogenicity (hypoechoic to anechoic), changes in fiber length and orientation, or enlargements of the structure. If insertional disease is suspected or visualized on the ultrasound, the insertion points (proximal metacarpus and sesamoid bones) should be radiographed to evaluate any bony abnormalities. MRI analysis of the suspensory apparatus is also sometimes utilized and may further pinpoint lesions that may not be apparent by any other diagnostic means.