Proximal Suspensory Desmitis


The suspensory ligament can be divided into three separate regions, all of which can become injured: the proximal (upper) part, the body and the branches. Proximal suspensory desmitis (PSD) or high suspensory disease, is a common injury in both the forelimbs and the hindlimbs of athletic horses and may occur in one limb or in both the forelimbs or both the hindlimbs at the same time.


Proximal suspensory desmitis in the forelimb results in a sudden onset of lameness which can be remarkably temporary, resolving within 24 hours unless the horse is worked hard. Lameness varies from mild to moderate and is rarely severe unless the lesion within the ligament is extensive. PSD in both front limbsmay result in loss of action rather than observable lameness. This occurs more commonly in racehorses, probably because of the failure to recognize earlier, subtle lameness of just one limb.
Lameness is usually worse on soft ground, especially with the affected limb on the outside of the circle. When subtle, the lameness may be more easily felt by a rider than seen by an observer. Lameness may not be apparent at working trot but may be detectable at medium or extended trot. Flexing the lower limb often temporarily worsens the lameness. It may be undesirable to work the horse hard to reproduce lameness because of the risk of worsening the injury.


If PSD is suspected, local diagnostic analgesia is indicated. This should result in substantial improvement in, or complete alleviation of, lameness within about 10 minutes, assuming PSD is the only cause of lameness. However, none of the different ways of blocking the proximal suspensory ligament are necessarily specific. That is, pain in other structures such as the knee or foot may also be alleviated. On the other hand, it is possible for the blocking solution to be injected into structures next to the proximal suspensory ligament. Thus, even if the lameness was not improved or alleviated with a PSD block, the lameness may still be due to this condition.


Diagnostic ultrasonography is essential to accurately diagnose PSD. The limb should be evaluated in two different planes and careful comparisons should be made to the opposite limb. High quality images are needed since lesions can be subtle and easily missed. Measurements of the ligament may be extremely valuable since, especially in acute cases, enlargement of the ligament may be the only detectable ultrasonographic abnormality. It may be difficult to evaluate an acute case accurately if the horse has had a previous injury to the suspensory ligament because the tissue may not have healed fully. Also, local diagnostic analgesia may allow air to enter the area, making visualization difficult.

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