There are two different types of windgalls, which are a soft swelling located to the rear of and slightly above the fetlock joint on a horse’s leg. This swelling is either an enlargement of the fetlock joint capsule (an articular windgall) or more commonly a swelling of the protective digital flexor tendon sheath (a non-articular windgall).
Windgalls are often dismissed as an inevitable side effect of an active life. Many apparently normal horses in full work have slight windgalls due to digital flexor tendon sheath swelling, particularly in the hindlimbs. The amount of swelling may vary according to the environmental temperature, being less obvious in cold weather and larger in hot weather.
The swelling may also be influenced by exercise. Work often results in some reduction in size, whereas stable rest may result in accumulation of fluid and greater swelling. However, repeated work on hard ground can lead to an increase in the size of the windgall.
Usually these swellings are similar in size between pairs of limbs, and symmetrical swellings are normally no cause for concern, provided they are cool to touch and not painful, and most importantly readily compressible with the fluid being moveable 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.
It helps to understand the anatomy: The tendon sheath encloses the superficial and deep digital flexor tendons, together with their attachments to the sheath wall. The membranous synovial lining covers the internal surface of the sheath, producing synovial fluid that contributes to both the health and lubrication of the enclosed structures.
If the sheath is damaged, it becomes inflamed and, synovial fluid production increases. This accumulated fluid can protrude from the leg at points where the tendon sheath is not constrained by other structures, causing a pronounced bulge towards the back of the fetlock.
Why do horses get windgalls?
Tendinous windgalls most frequently appear in response to hard work – particularly on hard ground – or increased exercise levels. They’re termed ‘reactive’, due to their association with general wear and tear.
Horses with poor conformation may be predisposed to developing windgalls. Poor hoof balance can also be associated. Horses that are worked on hard ground or deep going can develop the swellings, particularly when they are young. Injuries to the ligaments, tendons and the fetlock joint capsule can lead to windgalls developing, as can injuries to the articular cartilage in the joint.
If heat and lameness are present, the enlarged windgall is most likely ‘inflammatory’ – a more worrying development indicating underlying injury.
An inflammatory tendinous windgall usually affects one leg more than the others and is likely to be accompanied by a degree of lameness, although this may be subtle at first. This is called tenosynovitis and is relatively common.
Signs of windgalls
With an inflammatory tendinous windgall, the swelling will feel tense or hard and sometimes warm. It may be asymmetric in shape, if the sheath wall has been torn.
In general terms, the larger, warmer and more painful these windgalls are – that is, the more marked the amount of inflammation – the greater the degree of concern. The synovial lining reacts in proportion to the severity of the damage that has occurred, and in turn this dictates the nature and amount of synovial fluid produced.
Tears of tendinous tissue cause a small amount of bleeding into the sheath. This, and the torn collagenous tissue, then further irritates the synovial cavity and causes more inflammation.
Infection is potentially catastrophic in a digital tendon sheath. The risk of this will be greatest if a foreign body such as a thorn or splinter has penetrated the sheath, which can rapidly produce an acute inflammatory response within hours. Since this tendon sheath lies just under the skin at the back of the pastern, it is easily damaged. There may an obvious, large wound, but penetration by something small and sharp may not be immediately noticed.
Once infection enters an enclosed, fluid-filled area, such as the digital flexor tendon sheath, the body’s local defence mechanisms are unable to cope. Bacteria flourish and the area becomes septic – that is, overwhelmed by infection.
Early and accurate diagnosis with any tendinous windgall is the key to a successful outcome.
With the nature of the tissues involved, an ultrasound examination is critical. In experienced hands, this can reliably determine the nature of the fluid and the state of the soft tissues enclosed by and bordering the sheath.
Fluid with high levels of inflammatory cells and protein can be distinguished, identifying possible infection. Tears of the flexor tendons and their associated attachments can be identified, directing treatment and providing some degree of certainty about the likely outcome.
Ultrasound will also identify puncture wounds that can be impossible to find on clinical examination, and will highlight the presence of foreign material within the sheath. Foreign bodies appear as bright spots which reflect ultrasound. In some cases, as the waves cannot pass through them, they can create an underlying shadow.
Mineralisation of the soft tissues, which occurs with longstanding degeneration (usually over a period of years), creates a similar effect, but this is easily distinguished.
X-ray examination can be useful if there are concerns regarding bones adjacent to the sheath, most commonly the proximal sesamoid bones. It will also identify soft tissue mineralisation, although this will almost certainly have already been seen with ultrasound.
Taking a sample of synovial fluid from the sheath can confirm whether contamination or infection is present. In these cases, there will usually be marked increases in white blood cell numbers and protein content.
The presence of blood in the fluid can indicate tissue disruption or tearing. Blood clears from the synovial fluid very quickly, however, so this cannot be relied upon unless performed within a day or two of an injury.
Selecting the most appropriate treatment for any tendon sheath injury relies upon correct diagnosis. This is not always possible upon first examination, but it should always be the goal.
If the sheath wall is stretched (sprained), treatment should be directed toward reducing inflammation. As a general rule, inflammation aids healing by removing damaged cells and tissues. In this situation, however, it can cause further damage.
Persistent swelling may lead to a permanent increase in the amount of fluid produced or the pressure within the sheath. Development of scar tissue is another problem that can be detrimental to the eventual outcome.
Reducing tissue temperature by methods such as cold hosing or using ice boots can help. Counter-pressure bandages, controlled exercise and anti-inflammatory medication can also aid recovery, so treatment usually involves a combination of these.
Penetrating wounds and punctures resulting in infection require emergency surgical treatment to remove the foreign material and damaged tissue. Medical treatment such as antimicrobials are ineffective in eliminating infection inside a tendon sheath.
Medical treatments in the form of regenerative therapies are used in an attempt to repair the damaged tendon such as stem cells or platelet rich plasma (PRP), have been used anecdotally, although there is no scientific proof as yet of their effectiveness.
More conventional medications that can be injected into the sheath include hyaluronan (lubricating agent) and corticosteroid (anti-inflammatory treatment), which are commonly used in combination for some cases of non-infective inflammatory windgalls.
While this treatment may suppress some of the inflammatory changes, using it without an accurate diagnosis may actually lead to progression of the injury. There’s the additional risk, albeit remote, of introducing bacteria with the vet’s needle and causing a serious infection.
Vets have recognised for many years now that the healing of tendons within synovial cavities is even worse than in other areas of the body. This has been attributed to the synovial fluid. The sheath environment is selective, meaning that the cells and proteins necessary for the removal of damaged tissue and subsequent repair are effectively excluded. The torn tissue remains in the tendon sheath, where it causes on-going irritation and prevents healing.
From reviewing many cases, vets now have clinical evidence that the removal of this tissue through keyhole surgery, known as tenoscopy, can be very successful. The digital flexor tendon sheath is acknowledged as the most difficult structures in which perform this delicate operation, however, so extensive surgical experience is critical.
These are a different condition, where there is an increase in fluid within one or more fetlock joints. Somewhat similar to the more common windgalls involving the digital flexor tendon sheath, these may also be associated with the wear and tear of hard work. They are typically seen in stocky animals with upright confirmation.
Provided the fetlock joint swelling is not hot, tense, painful when squeezed or most importantly, not associated with lameness, they are usually acceptable. It might make sense to review the work load, check shoeing and hoof balance and continue to monitor, especially if only one joint is affected.
If a horse has a swollen fetlock joint and lameness, then your vet should be consulted. There are many possible cases, which include:
- Acute trauma, such as a joint strain
- Osteochondrosis (OCD)
- A bone chip or some other fracture.
A detailed clinical examination from your vet would be advisable. It may be necessary to obtain X-ray images or do diagnostic ultrasound to establish the cause. Once there is a clear diagnosis, then appropriate treatment can be selected.