HomeExpert AdviceArticleThe trouble with tendons

The trouble with tendons

Posted in Health and Veterinary

Tendon injuries are a common cause of lameness. Vet Gemma Sherlock advises on spotting, treating and preventing them in your horse

When we think about body movement we tend to focus on muscles, but tendons also play a vital part in movement, especially in animals such as horses who have no muscles in their legs below the knee and the hock. While there are many tendons throughout the body, those in the lower leg are specifically designed for effective locomotion. Unfortunately, they’re also particularly vulnerable to damage.

In essence, tendons are connective tissues containing strong collagen fibres with a small amount of elasticity. They connect muscle to bone and assist in movement of the relevant area. Any tendons in the body can suffer injury but, in the horse, the most commonly injured tendons are the long tendons of the distal (lower) limb. 

These are the flexor tendons and are comprised of the superficial digital flexor tendon (SDFT) and the deep digital flexor tendon (DDFT). Both are found at the back of the leg and run from the knee on the front leg and the hock on the hindleg. The SDFT ends at the back of the pastern and the DDFT ends on the pedal bone in the foot. At the back of the knee/hock and behind the fetlock, the tendons are enclosed within a fluid-filled tendon sheath that protects the tendons from injury as the joints move.

Injury prone

Tendons are strong, but they have relatively poor elasticity compared with other soft tissues such as muscle. Furthermore, the fact that they’re also repetitively put under huge amounts of force can make them prone to injury.

Tendon injuries most commonly occur during exercise, particularly in fast work or over uneven ground, and are often due to an overstretching of the tendon fibres. This overstretching can result in minor fibre disruption, a hole caused by an area of damaged fibres, or a tendon rupture. Horses are more likely to suffer tendon injuries if they’re not fit enough to perform the work being asked of them.

Direct trauma of some kind can also result in tendon damage. Blunt trauma, for example, may cause inflammation similar to a bruise, or even more severe damage such as tendon rupture. Sharp trauma caused by an external wound can result in laceration, usually of the SDFT. When a wound involves a tendon sheath, if an infection develops then the situation can be very serious.

Top tip

Check your horse’s legs on a daily basis so you become familiar with his usual lumps and bumps and can, therefore, quickly spot any changes. Be particularly alerted if you detect any warmth, as quick action could prevent a more serious injury.

Diagnosis and prognosis

Signs of tendon injury can vary, but may include lameness, pain when the area is touched and localised heat and swelling, which sometimes forms a bow (bulge) at the back of the leg, or a windgall (excess fluid in the tendon sheath). In severe cases, the fetlock may drop towards the ground and the toe of the foot may point upwards.

Examination by a vet may lead to suspicion of a tendon injury and ultrasound scanning will usually be advised. This may be delayed for around seven days following the injury, as damage is not always visible on the scan before this point. 

If there are no other clinical signs, nerve blocking and diagnostic imaging (X-rays and ultrasound scans) of a lame horse may be required to detect a tendon injury. Your vet may scan both legs, front or hind as appropriate, for comparison and to ensure that there are no areas of mild damage to the tendons in the seemingly unaffected leg.

Prognosis at this stage is dependent on the size and severity of the injury but may change depending on how well the tendon heals following treatment.

Did you know?

Blood supply to tendons is poor compared with other soft tissues such as muscle, which means healing can take a long time (9–12 months in some cases). 

Treatment plan

Treatment options vary depending on the type of injury and severity, but, unfortunately, no treatment guarantees resolution of the injury. Prolonged box rest may be required following a tendon injury.

In most cases, treatment involves rest, cold hosing (or ice boots), supportive bandaging and anti-inflammatories. Following a period of rest, a controlled exercise programme will be initiated and this will begin with the introduction of increasing periods of walking. 

During the healing process, ongoing monitoring of the horse’s comfort and regular ultrasound scanning is required to ensure that the tendon is healing and to assess when the time is right to increase the level of exercise. 

A controlled exercise programme is very important, as it can help the fibres to realign and retain some elasticity while they’re healing.

Top tip

When your horse is recovering from a tendon injury, walking in hand will help prepare him for gentle ridden work, the key being not to rush the rehabilitation process.

Explore the options

Other treatment involves injecting products into the damaged tendon, but this is usually only possible if there is a hole. These products neither speed up healing nor replace the need for a controlled exercise programme but they can help to improve the quality of healing by improving the fibre alignment and elasticity and, therefore, may reduce the risk of reinjury. 

Products that can be injected include platelet rich plasma (PRP) and stem cells. These are usually injected into the hole in the tendon under ultrasound guidance, using sedation and a nerve block to ensure that the horse stands still for the procedure. 

PRP – platelets are present in blood and are responsible for clotting. They also contain growth factors. A blood sample taken from the horse is processed using a special kit, then a small, concentrated amount can be injected.

Stem cells – stem cells are able to diversify into many different types of cells, including tendon cells. They are found in bone marrow and may be collected from the horse’s sternum or pelvis and are sent to a specific lab for processing prior to being returned for injection. Stem cells are now also available to purchase as ready to use.

In some cases, surgery is indicated. This is usually carried out for wounds associated with tendon injuries or injuries involving the tendon sheath. Your vet will advise if surgery is indicated for your horse and the pros and cons in his particular case.

Did you know?

When tendons heal, they create irregularly arranged fibres and scar tissue. This makes the tendon less elastic than it was prior to the injury, meaning that it is then weaker and more prone to being injured again in the future. 

Protect and prevent

The way in which horses are designed will always leave them at risk of a tendon injury, whether that’s when they’re turned out in the field or being ridden. Nevertheless, there are ways to minimise this risk…

  • ensure that the feet are well maintained and have good balance
  • avoid the horse carrying excess weight – this can be assessed with body condition scoring
  • ensure the horse is fit enough to perform the required workload – as fitness increases, the tendons adjust to the level of work and strengthen
  • avoid fast work on deep, boggy or very soft ground
  • tendon boots provide an extra layer of protection from trauma but will not prevent overstretch injuries

Top tip

Always adequately warm up before working your horse and cool down afterwards. A warm up/cool down should take around 10–15 minutes.

Take action

As with any injury in your horse, tendon injuries can seem daunting. It is often assumed that a tendon injury is career ending but this is not always the case. 

With prompt attention by a vet and appropriate treatment and rehabilitation, your horse may well be able to return to his previous level of athletic function. 

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