The word “windgall” is used to describe either an enlargement of the fetlock joint capsule, a so-called articular windgall, or of the digital flexor tendon sheath, the more common non-articular windgall.

Many apparently normal horses in full work have slight windgalls due to digital flexor tendon sheath swelling, especially in the hindlimbs. The amount of swelling may vary according to the environmental temperature, being less obvious in cold weather and frequently far more filled in hot weather.

The degree of distension may also be influenced by exercise. Work often results in some reduction in swelling, whereas stable rest may result in accumulation of fluid and greater swelling, which is often queried if the horse is being vetted for purchase.

Usually these swellings are similar in size between pairs of limbs, and symmetrical swellings are no undue cause for concern. These swellings in clinically normal horses are usually readily compressible and the fluid can be moved between different outpouchings of the tendon sheath. For example, if the top part of the tendon sheath is compressed by finger pressure, then increased bulging will be seen on the back of the pastern.

To some extent, the size of the windgalls can be controlled by the application of snug stable bandages, but daily use of stable bandages often results in ridges in the hair coat, a tell-tale sign of regular bandaging.

Windgall worries

Inflammation of the lining membrane of the digital flexor tendon sheath will result in increased production of synovial fluid and therefore swelling, seen as a windgall. This is called tenosynovitis and is very common. This can be sudden in onset as a result of overstretch of the tendon sheath because of a mis-step, or as a result of blunt trauma, for example, the horse getting a leg trapped over a fence. It usually results in the sudden onset of lameness.

Diagnosis is usually obvious, since the onset of lameness coincides with the development of swelling. There is localised heat and the horse may resent passive manipulation of the fetlock. The tendon sheath may feel very hard because it is being stretched by the amount of fluid within it.

Confusion arises because similar signs can be seen in association with damage to the superficial or deep digital flexor tendons, which are inside this tendon sheath. It is therefore prudent for a vet to check the tendons carefully using an ultrasound scan.

If no abnormality of the flexor tendons is found, I generally recommend treatment of the tendon sheath with a combination of corticosteroids, potent anti-inflammatory drugs, and hyaluronan. Hyaluronan is a normal constituent of synovial fluid and helps with lubrication of the tendons. The quality of hyaluronan decreases with inflammation. Injection of high molecular weight hyaluronan into the tendon sheath may help to normalise its own production.

I also apply a very firm, thick pressure bandage and restrict the horse to box rest. If there is no primary tendon injury, I expect to see very considerable improvement within a week, and with a slow resumption of controlled exercise, the prognosis should be favourable.

Tendon tears

Even with high-quality ultrasound scans, it is not always possible to detect all tendon injuries. Small tears on the margin of a tendon may be invisible. Damage to the tendons on the back of the fetlock at the level of the ergot will be missed because the ergot gets in the way of an accurate scan.

The presence of a tear in the tendon is likely to result in recurrent distension of the tendon sheath, and associated lameness when work is resumed.

I believe recurrence of lameness merits surgical intervention. An arthroscope, a telescope-like instrument, can be inserted into the tendon sheath so that the external surfaces of the tendons can be inspected and probed to identify damage. Torn fibres can be surgically removed. Consideration can also be given to cutting the palmar annular ligament to relive pressure on the digital flexor tendon sheath.

If short tears are identified, the horse may have a reasonable prognosis for return to athletic function, but the presence of long or deep tears warrants a more guarded outlook.

Tendon damage

In some horses, acute tenosynovitis is associated with strain injuries to either the superficial digital flexor tendon or the deep digital flexor tendon that can be detected using an ultrasound scan.

Injuries of the superficial digital flexor tendon occur most commonly in show jumping horses where the tendon is widest and thinnest and usually involve the margin of the tendon on the outside or inside.

Such lesions are easily missed when performing an ultrasound scan unless the scanner is moved round from the back towards the side of the limb.

These injuries occur much more commonly in forelimbs and usually respond well to rest, with most horses being able to return to full athletic function.

Deep digital flexor tendon injuries occur in horses from all disciplines and affect both hindlimbs and forelimbs. Dressage horses seem particularly at risk. Central core injuries range from small focal injuries within a normally sized tendon to large injuries associated with enlargement of the tendon.

Although small core injuries may heal spontaneously, with long-term resolution of lameness, the prognosis for large lesions is much more guarded. These may be candidates for treatment with stem cell therapy.

Tendon tears are not usually suitable for treatment with stem cell therapy because there is no normal tissue around the tear to keep the stem cells within the damaged tissue. These require surgical treatment, but often respond rather poorly.

Annular ligament damage

The main annular ligament itself can be injured by overextension of the fetlock. The ligament becomes swollen and painful. This may result in the development of a convex swelling on the back of the fetlock centred over the ligament. The swelling and pressure on the tendon sheath may cause secondary inflammation of the sheath, or, alternatively, the sheath may be injured at the same time.

Treatment such as anti-inflammatories, focal ultrasound therapy and rest may resolve the problem. But if marked enlargement of the ligament persists, constricting the tendon sheath, surgical treatment may be required. With severe injury, a reaction beneath the skin can cause the development of a layer of fibrous tissue between the skin and the palmar annular ligament. Such cases also usually need surgical treatment, but often respond less well.