Tendons and Ligaments: Possible Injuries and Long Roads to Recovery

Injuries to tendons and ligaments in horses’ legs are common and are the leading cause of loss of use in horses, whether competition mounts or pleasure companions.

These injuries can be stubborn and require the owner’s patience to see treatment and rehabilitation through for an extended duration. Even then, the horse might not be able to perform at previous levels. Luckily, however, there are many treatment methods and procedures that can improve a horse’s odds of a successful – but not necessarily quicker – recovery.

What are Tendons and Ligaments?

Tendons and ligaments are similar in construction. Both are comprised of a connective tissue made up of parallel bundles of strong elastic fibres that run lengthwise down the leg. The fibres are made mainly of collagen, a protein matter that is also found in other connective tissue such as skin and ligaments.

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Tendons join muscle to bone. They can stretch to a certain degree, allowing them to cope with strain. Tendons are enclosed in a sheath containing a fluid that allows the tendon to move smoothly over joints. Ligaments join bone to bone and give a joint stability. Together tendons and ligaments are responsible for holding the leg’s bones and muscles together, allowing the limb to function properly.

The Fab Four

Two tendons and two ligaments located at the back of the canon bone and fetlock perform the majority of the work in the leg and, therefore, are more prone to strain and injury:

Superficial digital flexor tendon (SDFT) – Visible at the back of the cannon bone, the SDFT connects the short pastern and the coffin bone. It stabilizes and flexes lower leg rearward. The majority of tendon injuries are to the SDFT.

Deep digital flexor tendon (DDFT) – Located just underneath the SDFT, the DDFT stabilizes the leg under full weight-bearing load, supports the fetlock joint and acts as a spring that stores energy when the horse moves.

Suspensory ligament – Runs from the back of the knee (hock in the hind leg) to the fetlock, located between the flexor tendons and the cannon bone. It stabilizes the leg under full weight-bearing load and prevents the fetlock from falling. Suspensory injuries are common and generally serious.

Inferior check ligament – Connects the deep flexor tendon with the cannon bone below the knee (hock in the hind leg), this ligament keeps tendons in place and prevents overstretching.

Susceptible to Injury

Despite their elastic tendencies and ability to withstand exertive forces, tendon and ligament fibres do possess a breaking point. When stretched beyond their capacity, they can tear, resulting in a strain (tendonitis) or sprain. With a strain, there is no tearing of any tissue. Swelling and heat are often minimal and the horse might not be lame. Sprains are more serious, as the connective fibres are torn or broken. Marked swelling occurs quite quickly following injury. The horse will likely be lame and the area will be sensitive to the touch. Other possible damage includes a full tendon rupture, which means the tendon can’t support the leg structure, resulting in the fetlock dropping toward the ground; lacerations that slice into tendons/ligaments; and an infected tendon sheath, which is very painful.

These injuries take a long time to heal and the risk of reoccurrence is very high, in part because the tissues have a poor blood and nutrient supply, which slows healing. Also, because the newly generated tissue is not the same type as the original, it heals randomly rather than in its normal parallel structure. The new tissue is comprised of a weaker collagen material that produces scarring, which is not as elastic or as strong and, therefore, compromises the strength of the tendon or ligament. “The junction of the normal tissue with the scar is never as strong as the normal tissue normally was. So what happens is, those horses heal and then they go back to work and then they tend to re-injure themselves at that junction,” said Charles McCauley, assistant professor of surgery at the Louisiana State University (LSU) veterinary school, home to the Laboratory for Equine and Comparative Orthopedic Research.

Injury to these soft tissues can be a result of a single traumatic incident or repeated forces that break down tendon or ligament structure. Many of the causes of strains and sprains are difficult to avoid, such as falls, slips, work on hard uneven terrain, a knock or blow or poor conformation. Others are avoidable – poorly trimmed/shod/balanced feet, repetitive concussion, repetitive trauma and incorrect boot or bandaging technique. But, overwork, either due to insufficient conditioning, rigorous training or working a tired horse too hard, is the most common reason injuries occur. Tired tendons lose their inherent elasticity and become strained.

While tendons in younger horses seem to be able to adapt to stresses, those in more mature horses appear to be far less likely to do so, especially when they are continually used to their limit of resilience, causing progressive degeneration, tearing and eventual failure of the tendon.

With the forelimbs carrying 60 to 65 per cent of the horse’s weight, most tendon and ligament injuries are found in the front legs, but the hind legs can also be affected. Such was the case with Audrey O’Handley’s Thoroughbred/Warmblood Justice, who suffered a hind-leg ligament tear in the fall/winter of 2010. The suspected cause was a kick from a pasture mate. “They told me it wouldn’t repair and it did,” said the owner from Stouffville, Ontario. “We beat the odds on that one. I was really happy.”

Know Normal

Early intervention can help prevent long-term serious damage. Knowing the landscape of your horse’s leg and how he moves before an injury will allow you to identify issues if they do happen.

Damage to tendons and ligaments causes inflammation – an accumulation of fluids and blood that is the body’s first response to injury. The more inflammation that occurs, the more the surrounding healthy fibres will become damaged due to the spread of bleeding, swelling and the release of enzymes that break them down. Feeling regularly for the hallmarks of inflammation – heat, pain and swelling – is one of best ways to catch tendon and ligament problems early.

Even mild symptoms are the first indication that something is going on. Taking action at this point can prevent fibres from tearing further and limit further inflammation response. Ongoing inflammation can lead
to serious damage as scar tissue is formed when the collagen fibres begin to repair.

Immediate First Aid

In the first 24 hours, the goal is to limit internal tendon damage by reducing inflammation in the following ways:

Cold therapy is considered the first-line of action. Ice packs, boots or wraps, cold hosing or an ice slurry applied to the site restricts blood flow, thereby reducing bruising and swelling. Generally, cold therapy is prescribed for three or four times a day for no more than 20 minutes at a time for up to 72 hours.
Stable bandages applied between treatments will apply pressure to reduce swelling and provide support.
A poultice can help draw heat out of the area.
Stall rest is essential at this point.
Within this initial, acute stage of injury, a veterinarian should assess the injury.

Diagnosing a Problem

O’Handley, a life-long horsewoman, who had taken all the right steps by icing, wrapping, limiting turnout and not riding when Justice was first hurt in August of 2010, said, “I probably should have consulted with a veterinarian first.” When she began riding again in September, the gelding came up lame. She was given the diagnosis of a torn ligament.

The veterinarian will likely use ultrasound, the main tool used to diagnose tendon and ligament injuries, to recommend the best course of treatment and determine the extent of damage. Ultrasound images are created as the echoes of high-frequency sound waves bounce off the body’s soft tissues. Normal tendon and ligaments appears white, while the location of injury will be black or grey, indicating blood and fluid accumulation and fibre tearing. The static ultrasound records can also be referred to in evaluating the progress of healing. Newer ultrasounds can provide 3-D images for increased accuracy.

Although more costly than ultrasound, magnetic resonance imaging (MRI) is sometimes used for diagnosis. MRI uses a strong magnetic field and radio frequency waves to produce detailed 3D images. Newer units allow the horses to remain standing without anesthesia.

Treating Injuries

The veterinarian will likely prescribe non-steroidal anti-inflammatory drugs such as phenylbutazone (bute), flunixin meglumine (brand name Banamine®) to reduce pain and inflammation. Other topical anti-inflammatories such as dimethyl sulfoxide (DMSO) and a cream called diclofenac sodium (trade name Surpass®) might also be prescribed.

As is advised in most cases, Justice remained on stall rest until the swelling and heat subsided while O’Handley rubbed a DMSO/corticosteroid combination into Justice’s leg twice a day and kept him wrapped when he wasn’t being treated.

Depending on the extent of the injury, this period can take up to two weeks. When the leg is no longer sore to the touch, rehabilitation begins.

Even if the horse no longer appears in pain, the tendon isn’t necessarily fully healed. Continued consultations with a veterinarian are critical, as every horse, injury and situation is different, and pushing the healing process risks re-injury. Rehabilitation must be slow and steady.

A controlled exercise regime is very important and involves hand-walking to start, very gradually building-up duration and level of intensity until the horse can be ridden. Eventual under-saddle workouts must be low-impact and also build slowly in length and difficulty. Turnout should be limited to a small paddock. The entire process can last six months to a year or more.

Although it was “way more work,” than turning to higher-tech, newer (and often unproven) therapies, O’Handley feels it was the simple act of massaging the injury location twice a day for five or ten minutes that helped her horse recover relatively quickly. “It brought the blood circulation to the area,” she said.

The treatments you consider will depend on the depth of your pocketbook, availability of therapies near your horse, and even whether your horse needs to return to his former work level. It is important to stress again that time and patience during convalescence and rehabilitation are essential rushing the process will provide your horse no benefit and could even cause more harm in the end. For Justice and O’Handley, recovery took five months, but it took her “a year to feel confident about it.”

An Array Of Additional Treatments

The veterinarian might also suggest one or more of the newer treatment strategies – including regenerative medicine, which augments the body’s natural processes to enhance healing – that are believed to help these complicated injuries.

Stem cells – Stem cells are immature cells that naturally mature into various body cell types. They are unique in that they can be readily divided and manipulated into specific cells for a particular part of the body and can then be transplanted to replace damaged tissue, promoting healing while reducing the chance of re-injury. They also contain many types of growth factors (proteins that cause cells to grow and proliferate and heal) as well as cytokines (chemical secreted by the cells of the immune system to attack infections and damaged cells).

Charles McCauley, assistant professor of surgery at the Louisiana State University (LSU) veterinary school, home to the Laboratory for Equine and Comparative Orthopedic Research, said the goal for veterinary practitioners and researchers is to get the tissue to heal “as close to its original architecture as we possibly can.”

A veterinarian extracts stem cells from a horse’s fat in the tailhead or from bone marrow taken from the sternum or hip. They are then isolated and multiplied and are re-injected into the injury site.

“There are some guidelines we have to follow,” said McCauley. “For instance, if the lesion is older than roughly 88 days, then stem cell therapy isn’t appropriate because usually there’s too much fibrous connective tissue that fills the void in that time, so there’s probably no added benefit to use stem cells after that point.”

Stem cells can also be collected from blood left in the umbilical cord and placenta after a foal is born and frozen until they are required. These stem cells have more potential to differentiate into cells of any type. They also last longer, are easier to obtain in larger numbers and aren’t affected by the horse’s own age and health in their ability to repair tissue. Their use is still only at the experimental stage.

Platelet-rich Plasma – Platelets are small portions of cells in the bloodstream that contain growth factors and are an important part of the body’s early response when an injury occurs. Platelet-rich plasma is the process of processing blood to extract the elements that contain the highest number of platelets. Blood is collected from the jugular vein, processed in a portable centrifuge to separate the platelets and the platelets are then injected directly into the injury site.

Extracorporeal shock wave therapy (ESWT) – A non-invasive treatment adapted from the technology used for many years to zap human kidney stones. The shock waves are believed to increase blood flow to the area, clear out damaged tissue, stimulate tendon fibre cell growth and promote proper alignment of tendon fibres.

Interleukin-1 receptor antagonist protein (IRAP) – An antibody against Interleukin-1, a protein secreted by many types of cells to attack other damaged cells and infection, which can be detrimental because it promotes inflammation and tissue deterioration. Blood is drawn from the horse with a syringe containing glass beads that stimulate production of IRAP and other proteins. It is then incubated for 24 hours, centrifuged and a protein-rich serum then injected into the joint. Considered minimally invasive, most rounds of treatment last about four weeks.

Surgery – Tendon splitting, performed shortly after the injury for best effect, drains blood and fluid from the site, encouraging healthy blood flow to aid in the formation of new tissue. Superior check ligament desotomy is thought to reduce strain on the SDFT and allow for greater elasticity. It is sometimes used in combination with tendon splitting.

Other – Hyperbaric oxygen chambers in which horses receive high concentrations of oxygen under pressure, are believed to increase the oxygen level in the blood and tissues. Some horses appear to benefit from water therapies such as aquatic treadmills, salt-water spas or swimming.