Tendon injuries

Tendon injuries can have a sudden and obvious onset (trauma, lameness). They also can be more insidious in onset. Minor overuse can cause microtrauma in the tendon, which weakens the tendon and sets off a vicious cycle of overuse and trauma. These types of tendon injuries may cause a lameness to be more subtle and harder to appreciate. Early detection of tendon injury leads to better recovery and prognosis.

Tendons and ligaments

Tendons are fibrous structures that form a connection between muscle and bone. They are passive structures that don’t contract like muscles do, rather they can convey the muscle’s contraction to a body part. There are no muscles in the horses’ lower legs. Tendons run through the lower legs to connect distant body parts to the muscles that make them move.

Ligaments are also fibrous structures. They form a connection between bones. They are also passive structures. Collateral ligaments make sure that bones stay in place and limit movement in unwanted directions. Other ligaments (eg annular) keep tendons in place. Ligaments like the nuchal ligaments (neck) and the suspensory ligaments (lower legs) maintain body posture. Ligaments play an pivotal role in the horses’ movement.

Tendons are made up of fibres that run longitudinally. Tendons don’t receive as much blood flow as other structures, such as muscles. Blood flow through tissues is responsible for nutrient supply and removal of the tissue’s waste products. Due to low blood flow, metabolism and regeneration are slow. This one of the reasons why recovery takes a long time.

The major tendons in the horse’s lower leg

The lower leg has extension and flexor tendons.

Front legs: Below the knee (carpus), the forelimbs have two extensor tendons: the dorsal (common) digital extensor tendon and the lateral digital extensor tendon. There are also two flexor tendons: the superficial digital flexor tendon and the deep digital flexor tendon. There are also two major ligaments: the lower/inferior check ligament (a.k.a. the accessory ligament of the deep digital flexor tendon) and the suspensory ligament.

Hind legs: Below the hock (tarsus), the hind legs have several extensor tendons (long digital extensor tendon, lateral digital extensor tendon, short digital extensor muscle) that come together to form one extensor tendon in the lower part of the cannon: (common digital extensor tendon). The hindlegs have the same flexor tendons and ligaments as the front legs.

Symptoms

An acute tendon injury often presents itself with lameness, swelling and heat where the defect lies. However, the severity of the swelling and lameness depends on the size and location of the injury. Some injuries only cause minor lameness, which may be overlooked. Swelling may be difficult to appreciate when the injury is small, or when deeper structures are affected (the suspensory ligament or ligaments in the hoof for example). Early detection is important to prevent the condition deteriorating. It is therefore important to check your horses’ legs daily and be mindful of any behavioral changes or irregularities felt during exercise. If a horse becomes lame during exercise, it’s important to immediately stop, cool the legs and call your vet.

Tendon injuries that have a more insidious chronic onset can be very hard to detect. As long as they stay undetected, the horse will try to take strain away from the area by shifting its weight and using different muscles to compensate. Over time, these compensations lead to muscle strain and other structures overworking. This helps to explain why research often shows that most back problems are caused by hoof lamenesses. If your horse is unwiling to work, stiff in the back, or “just not right” under saddle, have your vet check to make sure your horse is not suffering from a low grade chronic lameness.

Lameness after tendon injury may subside relatively quickly, within two weeks. Owners may start riding again, not knowing that the tendon has been damaged and hasn’t properly healed yet. This is how a minor tendon injury can become more severe.

Lameness exam

Your vet can do a lameness exam. This consists of observing your horse standing, walking and trotting in a straight line and on a circle, preferably both on hard and soft surfaces. Your vet may do flexion tests, in which your horses’ joints are flexed for a minute before trotting your horse in a straight line. Your vet will palpate the limbs, especially the lame one, looking for any signs of injury.

A lameness exam might also involve observing the horse while ridden or during a specific exercise. Depending on what’s found, your vet may perform nerve blocks to confirm where the pain is coming from. Xrays and ultrasound help visualize structures and help diagnose the underlying cause of the lameness.

Ultrasound

Tendon injuries can be visualized by ultrasound. In acute tendon injuries, the defect usually becomes bigger in the first period due to the body’s inflammatory response. Therefore, if your vet suspects a tendon injury, he/she may start you on initial treatment and come back to ultrasound the area 10 days after injury. More chronic injuries can be scanned straight away.

Your vet may be able to see swelling of the tendon and/or disruption of the tendon fibres. Tendons normally show as white firbous structures on an ultrasound screen. The fibres should all be aligned in the same (longitudinal) direction. Injuries may show as complete disruption of the fibres, leaving a black area or “hole” in the otherwise white firbous tendon tissue. Alternatively, tendon injuries may show as a more diffuse disruption of fibre alignment, with a more subtle change of intensity on the screen, a wider diameter, or the fibres may not all be aligned. Your vet will be able to show and explain to you what the defect looks like and measure how big it is. Recording and repeating ultrasounds is important to steer the therapeutic training schedule and monitor recovery. Depending on the type of injury, ultrasound may be repeated every four to twelve weeks.

Tendon injuries in the flexor tendons, check ligament, suspensory ligament and annular ligaments are relatively easily visualized due to their location. However, some structures may be very difficult to visualize, especially when located in the hoof. MRI is the best way to scan the structures inside the hoof. However, only Matama has an MRI available for horses in New Zealand. Massey Univeristy has a CT scanner, which may also be helpful in detecting certain hoof injuries.

The healing process of tendons

The first stage of healing is inflammation. The body clears away dead tissue and sets the scene for repair. This process takes about 10 days to 3 weeks depending on the injury. During this time the injury increases in size.

In the acute phase after injury, box/stall rest and cooling the area (for at least 15 minutes at a time) a few times daily are most important. Drugs can be used to control the inflammatory response and manage pain. However, non-steroidal anti-inflammatory drugs also inhibit the tissues’ healing process. They should therefore be used judiciously.

After this first (acute) phase of healing, the body will start to make new tissue. However, this tissue is not immediately functional tendon tissue. The body first fills up the defect with granulation tissue, the fibres of which are layed down in a cris-cross random manner. This tissue is very fragile and could easily get torn again if the horse moves too much or missteps. At the start of this phase, the process of healing that can be stimulated by platelet rich plasma (PRP), stemcell-, laser- or shockwave therapy (explained further down).

During this second phase of healing the horse needs to start in-hand walking to stimulate the body to strengthen the tissue. Care should be taken to not overdo the amount of exercise during this phase which could damage the new fragile tissue. However, the horse must be walked enough to stimulate healing. Repeated ultrasounds are important to assess the amount of work the horse can do safely. This phase of healing takes about 3 months, depending on the injury.

During the final phase of healing, the body adjusts fibre alignment to improve the tissue’s tensile strength. This process is also stimulated by movement. The horse will need to follow a controlled training program to facilitate strengthening of the tissue without overusing and damaging the new tendon tissue. The duration of this phase depends on the injury. Unfortunately, even if the tendon injury heals completely, the new tissue will never be as strong as the original tendon tissue. This doesn’t have to pose a problem. If the quality is good enough, the horse will be able to return to full performance. However, a proportion of horses may get re-injured due to overuse. Care must be taken to avoid this, by sticking to the rehabilitation schedule.

Why not just leave your horse in a paddock? Unfortunately, horses don’t understand that running around, playing in a paddock is detrimental to the healing process. We strongly advise you to combine restricted movement (rest) and a controlled exercise program to facilitate healing time and quality.

Treatment

As explained, in the acute phase box rest and cooling are very important. Anti-inflammatry drugs may be used. After the acute phase, the plan will depend on the injury. A controlled in-hand exercise program will be discussed. Further options include special shoeing, PRP injections, stemcell injections, aquatraining, lasertherapy, shockwave, etc.

Special shoeing

Special shoes can be made to shift the strain on the horses’ tendons during movement. That way, the healthy tendons can take on some of the weight from the damaged tendon to aid recovery. Special shoes are most effective on soft surface. A recovery plan may therefore involve specific instructions on whether the horse should be walked or trained on a hard or soft surface.

PRP therapy

PRP is short for Platelet Rich Plasma. Platelets are a component of the blood involved in blood clotting. They contain high levels of growth factors and other proteins, that stimulate healing. PRP inhances vascular growth, nutrition and collagen production and decreases inflammation. PRP treament has shown to shorten recovery time and improve tissue quality.

PRP treatment is done with the horses’ own blood. A blood sample is taken from the horse, after which the blood is processed to separate the plasma and platelets from other blood cells. The sample now contains high platelet numbers. For the injection it is very important thet the horse stands still, so sedation is necessary. Local anaesthetic and picking up another leg may also help. The PRP is injected into the defect under ultrasound guidance. One PRP treament is often enough, however treatment may be repeated depending on the injury.

Stemcell therapy

Stemcells are similar to embryonic cells, they are capable of developing into a multitude of different cell types. The tissue that surrounds them stimulates them to become the right cells for that tissue. Stemcells injected into tendon tissue will therefore be stimulated to develop into tendon cells or fibroblasts, which is the aim of this therapy.

Stemcells are taken from the horses’ own bonemarrow. A sample is taken from the sternum in the standing sedated horse. The sample is then sent to a lab where cell expansion techniques are applied to multiply the cells into several million cells. This process takes several weeks, depending on the age of the horse. The sample is then sent back to the treating veterinary practice, where the cells can be injected into the tendon defect under ultrasound guidance in the sedated horse. The cells can also be injected in the local blood vasculature (intra-arterial regional limb perfusion) when the tendon or ligament damage is located in the foot.

Injection of a high number of stemcells and the growth factors that accompany them improves healing time and tissue quality. Stemcell therapy can be used in tendon or ligament defects that have previously been prone to healing slowly with substandard scar tissue.

Shockwave therapy

Shockwave therapy has been proven to speed recovery in certain orthopaedic problems in human medicine. In horses, shockwave therapy has resulted in improved healing in injuries of the proximal suspensory ligament and hock problems. However, other orthopaedic problems, such as stress fractures, ringbone, navicular syndrome, back pain, and tendon injuries have been treated only with variable results. In a study at Iowa State University, horses with inflammation of the suspensory ligament were treated with shockwave therapy. The treated animals had a decrease in lesion area, improved fibre alignment, and less swelling than animals in a control group. A similar study in Germany compared shockwave therapy with conventional treatment (rest, cold treatment, blistering, application of anti-inflammatory and steroidal products). Of the conventionally treated group, 50% of the horses returned to full work within six months, while 71% of the shockwave group were able to resume full work in the same time period. In a third study group, horses with bone spavin (degenerative arthritis of the hock) were treated with shockwave therapy. A decrease in lameness was seen in 80% of the treated horses.

Shockwave can be very effective in certain injuries. It can also be used in certain chronic injuries to re-activate an old injury to kick-start the healing process again. Your veterinarian will be able to discuss the best therapy course for your horse.

Laser

Various studies show that laser therapy increases the production of collagen, improves the alignment of collagen fibres and increases the strength of tendons. A study on 150 Warmblood sport horses looked at the effects of laser therapy on acute or chronic superficial digital flexor tendonitis and suspensory desmitis. The horses received high-power laser therapy daily for two weeks. Each treated limb was clipped and degreased with alcohol before treatment, and the team performed follow-up clinical and ultrasound exams four weeks later. All horses improved in lameness score, with 80% sound at four weeks post-treatment. On ultrasound, 76% showed only mild or no abnormalities after treatment. The median time to return to low-level exercise was six weeks. Of all 150 horses, 55.8% had returned to their previous level of performance within six months. Reinjury rate after one year was 21%, which was comparable to other treatments. Results depend on the laser equipment used.

Prevention

When a horse has had a previous tendon injury, it becomes very important to make sure your horse has regular controlled exercise. Riding on unpredictable surfaces may pose a risk.

Tips to help prevent tendon injuries and detect them early:

• Make sure you exercise your horse on a good surface
• Always give your horse a good warmup (at least 10 minutes) at the start of exercise, especially in cold weather
• Slowly build up your training program for young horses, as tendons need time to adjust to increased weight (rider) and exercise
• Introduce new types of exercise gradually (jumping for example)
• Have your horses’ feet attended to by a proffessional farrier who can keep your horses’ feet balanced
• Feel your horses’ legs for warmth and/or swelling every day after exercise
• Cooling your horses’ legs after exercise may aid recovery
• Have your horse checked by a proffessional for competition season
• Always check unfamiliar grounds/arena at competitions pre-performance