Suspensory ligaments: Their vital role and the prognosis when damage occurs *H&H Plus*

The suspensory ligaments play a vital supporting role in athletic movement, so what’s the prognosis when damage occurs? Dr Rachel Murray MRCVS discusses outcomes

Running down the back of each cannon bone is the suspensory ligament, the tough, fibrous structure that supports the fetlock when the limb is loaded. The ligament starts just below the hock or knee and splits into two branches closer to the fetlock.

With the advanced imaging modalities now available, such as magnetic resonance imaging, we are more aware that not all suspensory ligament injuries are the same. Pain can come from the ligament and the bone where the ligament attaches – the cannon bone at the top and the proximal sesamoid bones at the bottom.

Suspensory ligament injuries may be caused by a sudden-onset single incident or repetitive overload. Damage at the top, or “origin”, of the ligament (proximal suspensory desmitis) is a risk in the hindlimb of the dressage horse, but possible in any sport. Damage in the middle, or “body”, usually occurs as an extension of injury at the origin or branches. Branch injuries may be caused by a twisting hyperextension of the fetlock or by direct trauma.

Certain conformational features and movement patterns may be associated with suspensory injury. A horse with a tendency to repeatedly and excessively extend his fetlock joints is at increased risk, which is related to his natural conformation and movement, the sport he does or his training.

Research shows that horses with straight hock conformation are more likely to have suspensory ligament injuries, due to hyperextension of the fetlock during locomotion. This places greater strain on the suspensory ligament, increasing risk of injury or reducing chances of recovery.

A horse trained to perform and repeat movements for which he does not have adequate muscle strength, endurance, flexibility or fitness will use the “wrong” muscle patterns and overload parts of his body to compensate for weakness. This can be exacerbated by poor core stability, placing strains on the lower limbs – including the suspensory ligament. Young horses with extravagant movement are particularly vulnerable: the “bigger” (faster or more extended) the trot, the more the fetlock drops and the greater the strain.

Treatment options

Early treatment of suspensory injury can lead to good recovery. However, some long-term or severe injuries can be frustrating to treat and difficult to manage.

Treatment is determined by many factors – where the injury is located, whether it is recent or involves longer-term scarring, if it affects bone and soft tissue, and any concurrent injuries. The horse’s age, conformation and sport must also be considered.

A severe bone injury is likely to need rest and hand-walking as part of a controlled rehabilitation programme. A mild bone injury may respond well to reducing the frequency and quantity of training, giving the bone time to recover between sessions, but still stimulating it sufficiently to repair the injured area.

Rest and controlled exercise alone can be a reasonable option for active branch injuries and forelimb proximal suspensory desmitis, depending on the severity of the injury, the horse’s age and the injury location. This may be less effective in hindlimb proximal suspensory desmitis, although I have had some good results rehabilitating young horses this way and following long-term turnout, particularly on hills.

High-intensity laser therapy has recently become available for horses and can help to reduce inflammation and promote healing in injuries of the branches, body and origin. Treatment with biological agents, including PRP (platelet-rich plasma), IRAP (interleukin-1 receptor antagonist protein) or stem cells, may also promote healing.

For horses with longer-term, chronic suspensory injuries, managing pain associated with scarring and repetitive strains at the attachment of the ligament becomes important. Extracorporeal shockwave therapy can be effective in removing pain and allowing the horse to move normally, alongside a programme of muscle development and ligament protection.

Horses with proximal suspensory desmopathy (a less inflammatory condition) who do not respond to other treatment, or those with chronic hind suspensory injury, may require surgical treatment. This can include resection (removal) of the tight band of tissue around the suspensory ligament, to help the ligament repair, or resection of nerves supplying this area, or both.

If surgical cases are carefully selected, it has been reported 78% can return to full work. But recent research and clinical experience suggests horses with a dropped fetlock or straight hindlimb conformation or both may not be good candidates for surgery.

Team tactics

At our clinic, we’ve found that a team approach to management can maximise recovery.

Eliminating pain helps prevent abnormal movement patterns that could have predisposed the horse to initial ligament injury. Retraining movement requires the development of correct neuromuscular pathways and the building of muscle strength and stability, which is a critical part of rehabilitation. Since the horse’s posture and core stability are key, the involvement of an Association of Chartered Physiotherapists in Animal Therapy (ACPAT) physiotherapist, who can work alongside the vet in the rehab process, is recommended.

Shoeing to support the ligament and help movement patterns is essential, tailored to the horse’s conformation and sport, as well as the surface on which he will be moving. A stable base reduces “wobble” of the leg, hock twisting and uneven fetlock extension, protecting the suspensory ligament. Increased support on the side of a branch injury will also help.

Careful management can be used to minimise the risk of re-injury. The more uphill and extravagant the horse’s movement, the more care must be taken. Both rider and trainer should recognise the importance of cross-training, core muscle development and avoiding over-repetition of exercises when a horse is tired.

Suspensory injury is a complex condition. There is increasing evidence that the best outcome relies upon a holistic approach, managing the biomechanics of the entire horse – and not just the ligament.

Steps to soundness

Charlie, an eight-year-old, advanced medium-level dressage horse, had always been slightly uneven in the contact and less keen on bending right. Following a hard training session, he developed swelling and heat on the outside of a lower forelimb and was unlevel when trotted in hand. The leg was treated with ice, cold hosing and pressure bandaging.

An ultrasound examination found swelling and active damage to the lateral (outside) suspensory branch, with some mild, long-term abnormality at the ligament attachment onto the proximal sesamoid bone at the fetlock. A combination of high-intensity laser therapy and cold treatment was chosen, along with shoeing to support the outside of the leg. Charlie’s physiotherapist had the job of teaching him to use his body more evenly, using stable exercises and ground work with specific training aids and tailored pole exercises.

A repeat ultrasound exam after six weeks showed considerable improvement. Controlled exercise was gradually increased, with check-ups to decide the pace at which to resume training.

Charlie is now back competing – achieving 72% in his first competition and winning at prix st georges. He feels more even in the contact, with improved lateral movement and quality of work, now that he is using his body more effectively.

The vet: Dr Rachel Murray is a veterinary specialist with particular expertise in advanced diagnostic imaging, poor performance and rehabilitation of sport horses. Rachel is based at Rossdales Equine Hospital and Diagnostic Centre in Newmarket, working in a team of sport horse clinicians. This world-renowned hospital sees horses and ponies from throughout the UK for diagnostic, medical, surgical and reproductive referrals. 01638 577754/rossdales.com

Ref Horse & Hound; 17 September 2020