Bit & Bridle

Equine Tendon Injuries

Other Names

  • Tendinitis
  • Tendinopathy
  • Flexor tendonitis
  • Bowed tendon
  • Soft tissue injury of the leg

What are Equine Tendon Injuries?

Equine tendon injuries are among the most common and career-limiting conditions affecting horses in work, particularly those involved in racing, eventing, showjumping, and polo. Tendons are dense, fibrous connective tissue structures that attach muscles to bones, transmitting the force generated by muscle contraction into movement. In the horse’s lower limb, they operate under enormous tensile loads and are vulnerable to both acute traumatic damage and chronic degenerative change.

The most frequently injured structures are the superficial digital flexor tendon (SDFT) and, to a lesser extent, the deep digital flexor tendon (DDFT). The SDFT runs down the back of the cannon bone and is the primary energy-storing structure at the gallop. When overstrained, the collagen fibres within the tendon tear — a process called tendinopathy — causing swelling, heat, pain, and reduced mechanical integrity.

The term “bowed tendon” describes the characteristic outward bulge visible along the back of the cannon bone when the SDFT is significantly thickened following injury. Learn more about related leg structures in our cannon bone terminology guide.

Causes

Tendon injuries arise from a combination of mechanical overload and biological vulnerability:

  • Acute overload: A single extreme event — a misstep, jump landing, or galloping on hard or deep ground — can exceed the tendon’s tensile strength and cause immediate fibre tearing.
  • Cumulative fatigue: Repeated sub-maximal loading without adequate recovery leads to microtrauma accumulation. The tendon begins to degenerate before any single catastrophic injury occurs.
  • Fatigue at end of exercise: As muscles tire, they lose their shock-absorbing capacity, placing a greater proportion of load directly onto the tendon. Many tendon injuries occur in the final stages of exercise.
  • Poor footing: Deep, boggy, or hard ground significantly increases tendon loading. Uneven surfaces can cause twisting or asymmetric loading.
  • Conformation: Horses with very upright pasterns, long toes, or low heels are at greater mechanical risk. Long cannon bones relative to forearm length also increases strain on the SDFT.
  • Shoeing issues: Imbalanced feet and delayed breakover increase the duration and magnitude of peak tendon strain.
  • Training errors: Rapid increases in workload, insufficient warm-up, or returning to full work too quickly after a lay-off all increase risk.

Symptoms and Signs

The classic signs of a tendon injury depend on its severity and whether the injury is acute or chronic:

  • Heat: Warmth along the back of the cannon bone is one of the earliest detectable signs
  • Swelling: Diffuse or focal swelling along the tendon — the hallmark “bowed” appearance in more severe cases
  • Pain on palpation: Tenderness when pressure is applied to the affected tendon
  • Lameness: Ranges from subtle at walk to severe; the horse may be reluctant to weight-bear on the affected limb
  • Fluid accumulation: Swelling of the tendon sheath (tenosynovitis) may accompany tendon injury
  • Chronic cases: A thickened, fibrotic tendon palpable as a firm, rope-like cord, often without acute heat or pain but with reduced athletic capacity

Diagnosis

A clinical examination by a veterinary surgeon is the starting point. This includes palpation of the limb, flexion tests, and observation of lameness at trot. However, definitive characterisation of a tendon injury requires imaging:

  • Ultrasonography: The gold standard for tendon diagnosis. Ultrasound allows the vet to assess the size of the tendon, the cross-sectional area, the architecture of the collagen fibres (echogenicity), and the presence of core lesions or tears. Serial scanning is used to monitor healing over time.
  • MRI: Provides superior soft tissue detail, particularly for injuries within the hoof capsule (DDFT, impar ligament, navicular bursa). Standing low-field MRI is now available at many equine referral centres.
  • Radiography: Used to rule out concurrent bony injury at tendon insertions.

Grading systems based on ultrasound findings help guide rehabilitation timelines. A lesion involving more than 25% of the cross-sectional area carries a significantly worse prognosis for return to full athletic function.

Treatment

Treatment is guided by the location, severity, and age of the injury. There is no shortcut — tendons heal slowly and inadequate rest remains the single most common cause of re-injury.

  • Immediate management: Cold therapy (cold hosing, ice boots), bandaging to limit oedema, and strict box rest. NSAIDs such as phenylbutazone reduce pain and inflammation in the acute phase.
  • Controlled exercise rehabilitation: Once the acute inflammatory phase has settled (typically 4–8 weeks), a carefully structured programme of hand walking gradually progressing to ridden work is introduced. This is guided by sequential ultrasound examinations — exercise is only progressed once adequate healing is confirmed.
  • Intralesional treatments: Platelet-rich plasma (PRP), bone marrow aspirate concentrate (BMAC), and stem cell therapies are used to try to improve the quality of tendon repair and reduce the formation of weak fibrocartilaginous scar tissue. Evidence for these treatments is growing, though large-scale controlled trials remain limited.
  • Surgical options: Tendon splitting (to encourage vascularisation of core lesions) and annular ligament release (where constriction is present) are performed in selected cases.
  • Shoeing modifications: Raised heel shoes reduce strain on the SDFT and are commonly used during rehabilitation.

Total rehabilitation from a significant SDFT tendinopathy typically takes 12–18 months before return to full work. Rushing this process dramatically increases re-injury risk.

Prevention

  • Train progressively — avoid sudden large increases in workload or distance
  • Warm up and cool down properly at every session
  • Maintain good foot balance and appropriate shoeing for the discipline
  • Avoid working on consistently poor footing
  • Use leg protection (boots and bandages) during exercise, particularly in high-impact disciplines
  • Monitor tendons regularly by palpation — early detection of heat or swelling allows prompt intervention before a minor change becomes a significant tear
  • Allow adequate recovery between hard sessions, particularly in horses competing at high intensity

Prognosis

Prognosis depends heavily on the severity of the initial injury, the horse’s age, discipline, and the quality of rehabilitation. Superficial core lesions in the mid-body of the SDFT have a reasonable prognosis for return to work with appropriate management, though re-injury rates are reported as high as 50–80% in racehorses. Horses competing at lower intensity levels (pleasure riding, light competition) generally have better outcomes. Injuries to the DDFT within the hoof capsule tend to carry a more guarded prognosis, particularly when the navicular bursa or distal sesamoid bone are involved.

When to Call the Vet

  • Any acute onset of heat, swelling, or pain in the lower limb
  • Noticeable lameness — even mild lameness in a horse with a history of tendon injury warrants prompt investigation
  • Any visible change in the profile of the back of the cannon bone
  • Before returning a horse to work after a lay-off if there is a history of tendon disease

Frequently Asked Questions

How long does a tendon injury take to heal in a horse?

Recovery times vary considerably by injury severity. Minor tendinopathy may resolve with 6 months of managed rehabilitation, while significant core lesions in the SDFT typically require 12–18 months before return to full athletic work. Cutting this timeline short is one of the leading causes of re-injury.

Can a horse with a tendon injury ever return to competition?

Many horses do return to their previous level of competition following tendon injury, though re-injury rates remain high in high-speed disciplines. The prognosis is considerably better for horses in lower-intensity work. Early diagnosis, thorough rehabilitation, and careful management on return to training all significantly improve the odds.

Is cold therapy useful for tendon injuries?

Yes. Cold therapy — whether through cold hosing, ice boots, or commercial cold-water circulating systems — reduces pain, limits swelling, and helps manage the acute inflammatory response. It should be applied for 20–30 minutes at a time in the immediate aftermath of injury and during early rehabilitation after exercise.

What is the difference between SDFT and DDFT injuries?

The superficial digital flexor tendon (SDFT) sits closest to the skin on the palmar (back) aspect of the cannon bone and is the most commonly injured tendon in sport horses. The deep digital flexor tendon (DDFT) lies deeper and continues into the hoof capsule where it attaches to the pedal bone. DDFT injuries are more common in horses with navicular syndrome and often require MRI for accurate diagnosis, as they are not fully assessable by external ultrasound.