One of the more common causes of chronic lameness is hindlimb proximal suspensory desmopathy (HPSD). Chronic referring to the continuous nature of the problem, as this is seldomly a problem diagnosed, treated, and resolved within a couple of weeks. It can start as an acute (sudden) lameness, but persist as an ongoing, performance-limiting lameness that may never resolve completely. Desmopathy equates to the disease of a ligament.
The hindlimb suspensory ligament (SL) is a ligament that attaches to the back of the cannon bone, just below the hock joint, and extends down the cannon where it bifurcates into medial (inside) and lateral (outside) branches, that each insert onto their respective sesamoid bones at the back of the fetlock. It is well tucked in between the hind splint bones and is covered by the superficial and deep digital flexor tendons. The body and the branches of the hindlimb SL are easily palpated but the proximal (upper) origin of the hind SL is not. The SL is part of the suspensory apparatus that is responsible for supporting the fetlock during movement.
Hind SLs are less commonly affected with pathology compared to the SLs in the forelimbs, but once affected they are often harder to manage than forelimb SL injuries.
Whilst many horses performing different forms of athletic activities suffer HPSD, horses with straight hindlimb conformation with hyperextended fetlock joints have been found to have an increase in the incidence of HPSB and a decrease in the success rate of treatments. A hyperextended fetlock is a fetlock that looks to be dropped lower behind when standing than a fetlock in the “ideal” position, and this conformation puts added strain on the ligament.
HPSD can be challenging to deal with as clinically it can present in different ways and can cause lameness or poor performance that persists for weeks to months. Sometimes, HPSD affects both hind SLs simultaneously, so lameness is not detected, but instead the horse loses hindlimb impulsion, shows poor transitions or stiffness when ridden. Other times the horse may just show behavioural changes and be reluctant to work, or bolt when ridden. Lameness, if present, may settle with time and then resurface when the work intensifies, or in some cases persist even with box rest.