Gayle Capps of The George Veterinary Group Equine Clinic on worrying injuries for horse owners.

Tendon injuries are rightly a worry for all horse owners.

This month, I thought I would try to explain what happens and what you can do if your horse suffers such an injury.

Tendon repair is an enormous subject, so next month I will talk further about current research and treatment options.

The four major structures below the carpus (knee) and hock, which can be associated with lameness if damaged, are the superficial digital flexor tendon (SDFT), the deep digital flexor tendon (DDFT), accessory ligament of the deep flexor tendon, more commonly known as the check ligament (CL), and suspensory ligament (SL).

Tendons differ from ligaments in that a tendon joins a muscle to bone, whereas a ligament joins bone to bone.

Both structures are dense bands of connective tissue, made up of a parallel arrangement of (type 1) collagen fibres.

The superficial and deep flexor tendons originate from above the elbow in the forelimb, and above the stifle in the hind limb, extending behind the carpus and hock respectively, after which they can be easily seen and felt as they run behind the cannon bone.

The superficial flexor tendon inserts on to the back of the pastern, and the deep flexor tendon inserts on to the underside of the pedal bone, which is the bone encased within the hoof wall.

The suspensory ligament arises from the back of the carpus/hock, and runs down the back of the cannon bone, between the splint bones, and then divides into two branches, just above the fetlock.

The check ligament also arises from the back of the carpus/hock, and joins the deep digital flexor tendon, about mid cannon level.

All these structures help to act as a spring, storing elastic energy and helping to move the horse forward.

They are very strong structures but not very stretchy, so if they are suddenly over-stretched, they can tear, and in some cases, rupture completely.

The majority of problems arise in the forelimbs as the horse carries 60 per cent of his weight on the forehand, and those horses doing fast work or jumping are at an even greater risk of damage due to the extra forces applied to the front legs.

When a tendon is damaged, there is usually heat and swelling evident.

The horse may or may not be lame. The damaged area of tendon is normally painful if squeezed, although some uninjured horses can be quite sensitive anyway.

Treatment will initially involve box rest, cold application, use of support bandages and oral anti-inflammatories, such as bute'.

An ultrasound examination is used to visualise the structure of the tendon, and ligaments and assess them for damage.

When we scan the tendons, in cross section they normally have a clear, obvious outline, a distinct shape and are uniformly grey' in appearance.

This is due to this regular parallel arrangement of the collagen fibres.

When a tendon has a tear, on scan we will find an area which is black, indicating a loss of these parallel fibres.

The greater the extent of the black area, the greater the damage and the longer the horse is going to have off work.

In the case of tendonitis (inflammation of the tendon), we may not find an obvious black lesion, but the cross- sectional area of the tendon will be enlarged.

For this reason, we will always scan the opposite limb to pick up subtle differences and for comparison.

Horses that have a distinct core lesion in their SDFT or suspensory branch may well be candidates for stem cell treatment - something I will discuss further in next month's issue. Once the horse is comfortable, we will commence a walking exercise programme for a period of weeks, from the box.

This is crucial for strengthening and conditioning the repairing tendon, and to encourage the new fibres to form the important parallel arrangement rather than a jumbled mass or - worse still - inelastic scar tissue.

After this, the horse is turned out in a very small paddock for a period of time, then a larger paddock.

Repeat ultrasound examinations will be performed at intervals to ensure that the tendon is healing well, and to determine when the horse can recommence work.

Frustratingly for you as the owner, your horse can often be sound, a few days after the injury happened, or never actually have been lame, yet be off work for months.

The important point is not to ignore any tendon swelling as it is often a warning sign of more going on.

Always call us if you are worried about a possible tendon injury because it is always better to be safe than sorry!