Hind limb proximal suspensory desmitis (PSD) is a common condition in sports horses and usually presents in one of three ways:

unilateral hindlimb lameness
bilateral hindlimb
no clear lameness but horse displaying rideability problems

PSD describes inflammation and / or damage to the upper region of the suspensory ligament at the top of the cannon bone where the structure mostly originates. Accurate diagnosis is challenging and requires careful interpretation of regional nerve blocking procedures, high quality ultrasound images of both the weight-bearing and non weight-bearing limb. Radiography should be carried-out to rule out co-existing bone pathology. Interestingly, low-field MRI which is the technology used in all the standing MRI units, is not very reliable for identifying suspensory pathology but is useful for picking-up more subtle bone lesions in the upper cannon bone region. Ultrasound scans can show enlargement of the proximal suspensory ligament, loss of fibre pattern and adhesions to surrounding structures.

Conservative treatment of PSD involving rest, medication and remedial shoeing is often not very effective.Unfortunately, surgery which entails removing a section of the deep branch of the plantar nerve and releasing the fascia surrounding the suspensory ligament is the only reliable treatment option giving a 70-80% chance of resolving the lameness providing any additional problems are also addressed; for instance around 40% of PSD cases are also found to have sacro-iliac pain. This essentially denerving surgery, should ideally only be performed on cases where there is minimal fibre disruption so that the structure of the ligament does not fail when it is subsequently, fully loaded post-surgery. This is particularly true for horses with a large hock angle i.e. those with a rather straight hind leg. Studies have shown that a hock angle of 165 degrees or higher is associated with an increased incidence of PSD. So next time you are contemplating a new purchase, take a protractor with you!

This large hock angle conformation predisposes to PSD