Is this the new 'bone spavin?'

But this has changed over the past 10-15 years with increasing recognition of suspensory ligament strains - especially to the proximal or upper part - as a common cause of lameness and poor performance, with a prevalence that now equals or exceeds that of bone spavin.

The suspensory ligament originates on the back of the cannon bone, just beneath the hock, and divides into two branches in the mid cannon region that insert onto the proximal sesamoid bones on the inside and outside of the fetlock joint. It runs down the back of the cannon bone, between the splint bones and underneath the flexor tendons and check ligament.

Function of the suspensory ligament is to hold or suspend the fetlock joint and stop the lower limb collapsing.

This is best illustrated by horses in which the suspensory ligament has completely failed: their fetlocks sink towards the ground during weight bearing. The two branches of the ligament also work to stabilise the fetlock joint and prevent twisting type strains.

Injury can occur to the proximal portion, the mid region, or one or both of the suspensory branches. The former, which is referred to as proximal suspensory desmitis - PSD for short - is the most common site of injury in the hindlimb.

Increased diagnosis of PSD in recent years has been linked to several factors. First, with advancements in nerve block techniques and diagnostic imaging, we have undoubtedly gotten better at seeing where the problem is.

Secondly, there has genuinely been an increase in frequency of occurrence of PSD. This has in turn been blamed on modern training techniques and surfaces as well as increasing athletic demands, especially in dressage horse and show jumpers, and the fact that we are breeding bigger moving horses.

The value of elite dressage and jumping horses, now running into tens of millions of pounds, is such that there is temptation to wrap them in cotton wool spending their time in a stable, on an exerciser or being ridden on an artificial surface. They are not exposed to the mixture of work and variety of surfaces that formed the core of older training methods and which traditionalists argue strengthen legs.

Clinical signs of PSD are variable ranging from sudden onset lameness that can be mild to severe in nature, to poor performance or reluctance to work without obvious lameness. One or both hindlimbs may be affected to similar or varying degrees.

Typical indicators of PSD include loss of impulsion, stiffness, resistance or reluctance to go forward, unusual refusals jumping, or difficulty performing dressage movements that once attracted good scores.

Horses with PSD may be 'short behind' with a short stride, low foot flight and dragging of the toe. This may be more obvious when lunged or ridden on a circle and is often exacerbated by flexion of the hock region. Many subtle cases of PSD, particularly when both hindlimbs are affected, can go undetected because there is not obvious lameness.

The fact that the proximal suspensory ligament is hidden between the splint bones makes it difficult to palpate manually. Nerve blocking is essential for diagnosis of PSD and this involves injecting local anaesthetic around the suspensory ligament under the hock.

This usually alleviates pain in 10-15 min, abolishing lameness or improving gait. It may be necessary to nerve block both limbs to see the full effects as I found in a recent case.

This dressage horse was becoming difficult to ride, unhappy to work and just not living up to his potential. While not obviously lame there was a shorter right hind stride when ridden but the rider said the horse felt 'more unusual' after the right proximal suspensory was nerve blocked. She was, however, delighted to have her 'old horse back' when the left was then blocked and subsequently spent 10 min enjoying the lovely moving dressage horse she realised she hadn't had for well over a year!

The structure of the proximal suspensory is easily visualised with modern digital ultrasound scanners, allowing assessment of the severity and likely timescale of injury. There is often enlargement of the ligament with loss of normal fibre pattern. Mineralisation of the ligament and roughening of the cannon bone at the site of origin are indicators of more long-standing injury and poorer outlook.

There may also be change on x-rays and bone scanning if this is also done as part of the diagnostic investigation. Care should be taken to differentiate PSD from pain originating from the lower hock joints. It is also important to realise that PSD often occurs in conjunction with sacroiliac joint pain.

Treatment largely depends upon the degree and duration of damage to the proximal suspensory ligament. Underlying factors, time constraints, athletic expectations and financial considerations can also be important factors.

Signs rarely resolve with rest, probably because the suspensory ligaments are loaded even when simply standing in the stable, and less than 20% of horses will recover with rest alone.

Horses with recent injuries (less than 4-6 weeks) often respond well to local injection of corticosteroids, which reduce inflammation and swelling.

Extracorporeal shock wave therapy improves outcome to around 40% but continued treatments may be required.

Biological products that stimulate healing are now frequently used, either alone or in combination with other treatments. Platelet-rich plasma is currently favoured as it contains a number of growth-promoting factors. Stem cell therapy is an option too.

Tildren, or Equidronate as it is now called, is also useful in cases where there is boney changes. Veterinary treatments can result in 80% of horses returning to work when used in conjunction with appropriate rehabilitation and controlled exercise to strengthen the ligament.

Surgical treatments are recommended for severely affected horses or those that do not respond to conservative and medical management.

The most popular operation involves cutting the fascia that covers the ligament - thus relieving pain associated with a swollen ligament in a confined space - along with the nerve that senses pain from the proximal suspensory region.

Long term follow up of surgical cases indicates that over 80% return to previous levels of athletic activity. But, as with other treatments, it is important to recognise and correct any predisposing factors or concurrent diseases.

So, what about the forelimbs?

Anatomy and function of suspensory ligaments in front is similar to behind but injury to the proximal portion tends to result in sudden onset lameness, which often resolves with rest.

It may grumble with low grade discomfort that may not be obvious as lameness, but rather causes a loss of action, and is often associated with foot imbalance or pain reflecting a compensatory type injury.