Tendon Injuries in Horses
What is a tendon injury?
Tendons are strong, slightly elastic bands of tissue that connect muscles to bones. They transfer the force produced by the muscles so that the horse's joints and limbs can move.
In the lower limb, some tendons also act rather like springs. They stretch slightly as the limb takes weight and then release that stored energy as the horse moves forward. This is one reason horses can move so efficiently – but it also means these tendons can experience considerable forces during exercise.
A tendon injury occurs when some of the fibres within a tendon become damaged. The injury may range from relatively small areas of fibre disruption to much more extensive tearing.
Owners may hear terms such as tendon strain, tendon lesion, core lesion, bowed tendon or superficial digital flexor tendon injury. These terms can sound complicated, but they are usually describing which tendon has been affected, where it has been damaged and how much of its internal structure has been disrupted.
Tendon injuries should always be taken seriously. Appropriate veterinary assessment and a carefully managed rehabilitation programme are important because tendon tissue heals relatively slowly and the repaired tissue may not initially have the same structure or strength as the original tendon.
The tendons owners most commonly hear about
Several tendons run down the horse's limb, but two names are particularly likely to be mentioned when discussing injuries to the back of the lower leg.
Superficial Digital Flexor Tendon – SDFT
The superficial digital flexor tendon, often shortened by vets to SDFT, runs down the back of the limb.
It is particularly important in supporting the limb and storing and releasing energy during movement.
When somebody refers to a superficial flexor tendon injury, they mean that fibres within this tendon have been damaged.
This is one of the tendon injuries most commonly associated with horses undertaking faster or more strenuous exercise, although it can occur in horses performing many different activities.
Deep Digital Flexor Tendon – DDFT
The deep digital flexor tendon, usually shortened to DDFT, lies deeper within the limb and continues down into the hoof.
An injury to the DDFT can therefore occur higher in the limb or within structures enclosed by the hoof.
Owners sometimes find this confusing because a horse may have a deep digital flexor tendon injury within the foot, even though there is nothing externally visible on the leg.
Imaging such as ultrasound or, in some cases, MRI may be needed to establish exactly where the damage is located.
What does a vet mean by a "tendon lesion"?
The word lesion simply means an area of abnormal or damaged tissue.
In a healthy tendon, thousands of collagen fibres are arranged in a highly organised pattern, largely running in the same direction. This arrangement gives the tendon its considerable strength.
When a tendon is injured, some of those fibres can become overstretched, disrupted or torn.
On an ultrasound examination, the vet may be able to see the damaged area and describe it as a lesion.
So if your vet tells you that your horse has a tendon lesion, it does not mean that something separate is growing within the tendon. It generally means that an identifiable area of the tendon's normal fibre structure has been damaged.
What is a "core lesion"?
Owners may also hear the expression core lesion.
This describes an area of damage occurring within the central part, or "core", of the tendon.
Imagine a strong rope made from thousands of tightly organised fibres. If some fibres within the centre of the rope become damaged while the outside remains more intact, there can be an internally weakened area even though the structure has not completely failed.
That is broadly what the term core lesion is describing.
The size and location of the lesion help the vet assess the extent of the injury and monitor how it changes during rehabilitation.
What is a "bowed tendon"?
A bowed tendon is an older but still commonly used expression, particularly for injuries involving the superficial digital flexor tendon.
Following injury, inflammation and swelling can cause the normal straight outline at the back of the lower limb to become curved or "bowed".
The visible swelling is therefore a consequence of the underlying tendon injury, rather than a separate condition.
Not every tendon injury produces an obvious bow, and an apparently normal-looking leg does not rule out tendon damage.
What actually happens when a tendon is injured?
A tendon is designed to tolerate considerable loading, but there is a limit to how far its fibres can safely stretch.
Damage can occur when the force placed through the tendon exceeds what its fibres can tolerate. Sometimes this happens during a single event. In other cases, repeated loading may cause microscopic damage to accumulate over time.
Once fibres are damaged, the body begins an inflammatory and repair response.
Initially there may be:
- heat
- swelling
- pain
- disruption of tendon fibres
- bleeding and fluid accumulation within the damaged area.
The body then begins repairing the injury by producing new collagen.
However, repaired tendon tissue is not immediately identical to the original highly organised tendon. Early repair tissue is less organised and needs time and carefully controlled loading to remodel and strengthen.
This is why tendon rehabilitation is generally measured in months rather than weeks.
What might an owner notice?
The signs can vary considerably depending upon which tendon is affected and the severity and location of the injury.
You might notice:
- heat in part of the limb
- swelling or thickening along the tendon
- sensitivity when the area is touched
- a change in the horse's movement
- reluctance to work normally
- reduced performance
- a change in the shape or contour of the back of the leg.
With some injuries, the horse may initially show a very noticeable alteration in movement. With others, the signs may be surprisingly subtle.
A tendon injury should therefore not be judged simply by how dramatically the horse appears affected.
Why do tendon injuries happen?
There is rarely one single explanation that applies to every horse.
Factors can include:
Sudden excessive loading
A tendon may be overloaded during fast work, jumping, slipping, landing awkwardly or another sudden movement.
Repetitive loading
Small amounts of microscopic damage can accumulate when a tendon is repeatedly subjected to strenuous exercise.
Fatigue
As muscles become tired, their ability to help control and stabilise the limb may reduce, potentially changing the forces being transmitted through tendons.
Previous tendon injury
Previously injured tendon tissue may have different mechanical properties from completely healthy tendon, which is one reason carefully controlled rehabilitation is so important.
Ground and workload
Changes in surface, speed, intensity, duration and type of work can alter the forces passing through the limb.
Age and tissue condition
Tendon structure changes over time, and an older tendon may not respond to loading in exactly the same way as that of a younger horse.
Usually it is more useful to think about the combination of loading, conditioning, tissue health and circumstances than to search for one simple cause.
How are tendon injuries diagnosed?
If a tendon injury is suspected, veterinary assessment is important.
The examination may include feeling the limb for heat, swelling, pain and changes in tendon contour, together with assessment of the horse's movement.
Ultrasound
Ultrasonography, usually simply called an ultrasound scan, is commonly used to examine tendons.
It allows the vet to look at the internal fibre pattern and assess the position and approximate extent of damaged tissue.
Owners may hear their vet discussing:
- fibre pattern
- cross-sectional area
- lesion size
- echogenicity
- core lesions.
These are different ways of describing what the tendon looks like internally and how much its normal structure has changed.
Repeat ultrasound examinations may be used during rehabilitation to help assess healing.
MRI
Magnetic resonance imaging – MRI – can provide detailed images of structures that may be difficult to assess fully using ultrasound, particularly within the hoof.
This can be particularly useful when investigating some deep digital flexor tendon injuries.
Treatment and rehabilitation
Treatment depends upon the tendon involved, the extent of the injury, the horse's circumstances and its intended future workload.
The attending vet should determine the appropriate treatment and rehabilitation programme.
During the early stages, management may concentrate on controlling inflammation and preventing further damage.
The longer-term objective is then to encourage the developing tendon tissue to organise and strengthen.
Controlled exercise
Owners will frequently hear the term controlled exercise during tendon rehabilitation.
This is not simply about "keeping the horse moving".
Carefully controlled loading provides mechanical signals that help healing tendon fibres organise appropriately. Too little loading may not provide enough stimulus, while excessive loading can damage tissue that is not yet strong enough.
A programme may therefore progress gradually from periods of controlled walking through increasing amounts and types of exercise.
Progress should be determined by the horse's veterinary team rather than by a fixed timetable taken from another horse's rehabilitation programme.
Why does tendon rehabilitation take so long?
One of the most difficult aspects for owners is that the horse may appear comfortable long before the tendon has regained sufficient strength.
Visible swelling may reduce and the horse's movement may look much better, but healing is still taking place inside the tendon.
Collagen fibres need time to remodel, align and mature.
This is why returning a horse to strenuous exercise simply because the leg looks better can significantly increase the risk of reinjury.
The rehabilitation period is therefore part of the treatment – not simply a waiting period before the horse goes back to work.
Can tendon injuries happen again?
Unfortunately, reinjury is an important concern following significant tendon damage.
The aim of rehabilitation is to encourage the best possible repair and progressively prepare the tendon for the forces it will experience when the horse returns to normal activity.
Risk cannot be removed completely, but sensible management may include:
- following the veterinary rehabilitation programme
- increasing workload progressively
- avoiding sudden increases in speed or intensity
- maintaining appropriate overall fitness
- monitoring the limb for changes
- considering the surfaces on which the horse works
- responding promptly if heat, swelling or altered movement develops.
Tendons, muscles and the rest of the horse
A tendon does not work independently.
Muscles generate force, tendons transmit it, joints move and the hoof interacts with the ground. The horse's whole musculoskeletal system therefore works as an interconnected unit.
During rehabilitation, changes in exercise and movement can also affect other parts of the body.
Maintaining appropriate muscular condition and gradually restoring whole-body fitness are therefore important parts of returning the horse to work.
Supporting the horse nutritionally
Good nutrition cannot repair a torn tendon by itself and supplements should never replace veterinary treatment or controlled rehabilitation.
However, a horse recovering from injury still needs an appropriately balanced diet providing the nutrients required for normal tissue maintenance and repair.
This becomes particularly important during prolonged periods of reduced exercise or box rest, when the horse's energy requirements may fall considerably while its nutritional requirements still need to be met.
Where a FreeStep product is specifically appropriate to supporting musculoskeletal health or the nutritional requirements of a horse undergoing rehabilitation, it should be presented prominently here with a clear explanation of its intended nutritional role.
Product claims must remain within the product's authorised purpose and should never suggest that a supplement treats or heals the tendon injury itself.
When should I call the vet?
Seek veterinary advice promptly if you notice sudden heat, swelling, pain or a significant change in your horse's movement, particularly following exercise.
You should also contact your vet if a horse already undergoing tendon rehabilitation develops new heat, swelling, discomfort or a deterioration in movement.
If you are unsure whether a change is significant, it is generally better to have the horse assessed than to continue exercising a potentially injured tendon.
Suggested Graphics
Graphic 1 – HERO: "Understanding a Tendon Injury"
Purpose: Main page graphic and capable of being used independently as an educational image.
Visual: A clean anatomical illustration of the lower horse limb showing the superficial digital flexor tendon and deep digital flexor tendon. Beside it, a magnified cutaway compares organised fibres in a healthy tendon with disrupted fibres in an injured tendon.
Key labels:
- Superficial Digital Flexor Tendon – SDFT
- Deep Digital Flexor Tendon – DDFT
- Healthy organised tendon fibres
- Area of damaged/disrupted fibres – "tendon lesion"
Plain-language message on graphic:
A tendon injury means that some of the normally organised fibres within the tendon have been damaged.
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Graphic 2 – "What Does a Core Lesion Mean?"
Purpose: Explain terminology owners may hear following an ultrasound examination.
Visual: Cross-section and lengthways illustration of a tendon. The normal tendon is shown alongside one containing a clearly defined central damaged area.
Labels:
Healthy tendon
Fibres organised closely together.
Core lesion
An area of damaged fibres within the central part of the tendon.
Supporting wording:
"Lesion" simply means an area of damaged or abnormal tissue. A core lesion describes where that damage is located – it does not mean something is growing inside the tendon.
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Graphic 3 – "Tendon Healing Takes Time"
Purpose: Help owners understand why rehabilitation continues after the horse appears more comfortable.
Visual: Simple three-stage progression:
1. Injury & inflammation
Fibres disrupted – heat and swelling may be present.
2. Repair
New collagen forms, but the developing tissue is initially less organised.
3. Remodelling & strengthening
Carefully controlled loading helps fibres organise and mature.
Central message:
The horse may look better before the tendon is ready for normal work.
Bottom statement:
Controlled rehabilitation is part of tendon treatment. Follow the programme provided by your veterinary team.
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Important
This information is intended to help horse owners understand tendon injuries and terminology they may hear from their veterinary surgeon or other equine professionals. It is not intended to diagnose an individual horse or replace veterinary advice.
Tendon injuries vary considerably in location and severity. If you suspect your horse has sustained a tendon injury, seek veterinary assessment before continuing exercise.