Equine Matters Spring 2019

15 Equine Matters Spring 2019 Suspensory ligament Fellowes Farm Equine Clinic Ltd V E T E R I N A R Y S U R G E O N S logoswith riderelement clipping .tif David Rutherford BVM&S Cert ES(Orth) DipECVS MRCVS European and RCVS Recognised Specialist in Equine Surgery Fellowes Farm Equine Clinic The purpose of the suspensory ligament is to support the fetlock during weight bearing. Injuries of the suspensory ligament are common in forelimbs and hindlimbs of horses. Lesions are typically classified as affecting the proximal, body, or branches of the suspensory ligament. Anatomy and Function The suspensory ligament is similar in the front and hind legs of the horse. It starts on the back of the cannon bone just below the knee or hock, and runs down to attach on to the sesamoid bones at the back of the fetlock. The top part of the ligament (the proximal region or origin) and the middle part (the body) run down as a single structure before splitting into two branches above the fetlock. One branch attaches to the inside of the fetlock and the other to the outside, at the sesamoid bone (Figure 1). When working with the distal sesamoidean ligaments, the purpose of the suspensory ligament is to support the fetlock during weight bearing. As a horse puts weight on its foot, the fetlock bends, and it is the job of the suspensory ligament to stop excessive joint flexion. Without the support of the suspensory ligament a horse’s fetlock would collapse down to the ground during weight bearing. Mechanism of Injury Suspensory ligament strains are often a type of repetitive strain injury. Repeated exercise and training cause micro-damage to occur within the ligament, so that it gradually weakens. Certain conformation abnormalities and training regimes magnify this effect so that the micro-damage worsens and horses are then at risk of developing a strain. Strain can also occur after an abnormal loading event, such as landing awkwardly after a jump or a field accident. Injuries can occur at any location within the suspensory ligament, but are most common at its upper and lower margins where it attaches to the cannon bone and sesamoid bone respectively. Signs of Injury Depending on the location and severity of injury, lameness, heat, swelling and ‘pain to pressure’ are often present. In some cases these signs are not noticeable and instead only a slight loss of performance is observed, such as disuniting in canter. This is particularly true for strains to the upper part of the ligament in the hind leg. Careful palpation, lameness evaluation and nerve blocks are often used to investigate the problem, with ultrasound examination usually giving the final diagnosis. Damage in the suspensory ligament will show as an enlarged cross sectional area (swelling), loss of regular fibre pattern and black holes if injury is more severe (Figure 2). Desmitis - Suspensory ligament strains Figure 1: Anatomy of a horse’s front leg when viewed from the side. The suspensory ligament, sesamoid bones and distal sesamoidian ligaments act as a single unit to prevent over extension of the fetlock joint during weight bearing. Knee joint Splint bones Suspensory ligament origin Cannon bone Suspensory ligament body Suspensory ligament branches Sesamoid bones Distal sesamoidian ligament Long pastern bone Short pastern bone Navicular bone Pedal bone