This study focuses on the effectiveness of various diagnosis challenges related to injury and lesions on the suspensory ligament. Proximal suspensory desmitis (PSD) makes reference to any injury of the suspensory ligament on the proximal third of the third metacarpal (cannon bone).
In the forlimbs PSD is often characterized with sudden onset lameness or is extremely subtle and the lameness is only visible at higher speeds until the injury progresses past recovery. Within the eventing community of which I was a part of the latter was often the case as riders and trainers would continue to push their horses thinking that the subtle lameness was simply stiffness or muscle soreness. This is why it is so critical to find effective ways to effectively diagnose PSD. PSD is most common in older competition horses and young “exuberant” horses and when not sudden onset lameness due to acute injury, PSD is most commonly found on both forelimbs. In more obvious cases localized heat and swelling on the limb.
In the hind limbs PSD very subtle and according to this article many riders and trainers characterize the symptoms as poor performance rather than obvious lameness. Unfortunately this often prompts harder training efforts, rather than PSD treatment. The symptoms include loss of impulsion, loss of power when jumping, out of character jump refusals, inability to perform dressage movements including pirouette. In my horse Batman, the biggest symptom was seen as inability to perform piaffe, haunches in and full pass.
PSD is not only harmful because of its impact on the suspensory ligament, but because of the secondary injury which it can cause, as the horse under or over compensates in other area of its body. It often causes sacroiliac joint and thoracolumbar region problems.
A common visual test for identifying PSD is to lunge the horse in a riding arena or area of soft footing. When visually assessing PSD in the forelimb, lameness will be more evident when the horse moves in soft footing, and if not bilateral, when the impacted leg in on the outside of the circle. The horse is often asked to work hard on the lunge line as lameness may not be seen at working trot, and will be more evident at medium or extended trot. The visual test is not always effective, as often the lameness is so subtle it is easier felt by the rider then visually seen by a skilled observer.
After a visual assessment, many veterinarians use a technique called local analgesic or nerve blocking. PSD visual symptoms will worsen after blocking, while other leg ailments such will likely improve, as the nerve block will showcase the ligaments inability to perform when the horse is no longer in pain. However, this has a high rate of false positive results.
Another common assessment is to take ultra sound images. According to this study an ultra sound image will show up as: enlargement of the cross sectional area; poor demarcation of the margins; focal hypoechogenic or anechogenic core lesions; reduced strength of fibre pattern; focal mineralization and new bone on the palmar cortex of the cannon bone. In my experience, it can be difficult to diagnose PSD in a short period of time as many vets want to perform each of these tests on different day; this study confirms this as they suggest that nerve blocking may impact the quality of images.
This study further established that radiographs should not be used in diagnosis as there is often no radiographic distinction. Nuclear scintigraphy can be effective in conjunction with the the more common visual and ultrasound assessments. Radiopharmaceutical uptake is altered in damaged tissue; however there is a 75% chance that a horse with PSD will not have altered radiopharmaceutical uptake. MRI is another possible assessment however, the interpretation of PSD in complicated due to the increased signal intensity of ligamentous tissue.
Although this study does not speculate which methods are more effective, after reading the evidence presented it is clear that visual and riding assessments coupled with ultra sound imaging, is the most direct and effective way to diagnose PSD.
Dyson, S. (2007). Diagnosis and management of common suspensory lesions in the forelimbs and hindlimbs of sport horses. Clinical Techniques in Equine Practice, 6(3), 179 – 188.