The horse’s tendons are prone to strain injuries, especially when participating in disciplines, such as racing, jumping and eventing.

Tendons are fibrous connective tissues that attach muscle to bone and allow the limbs to move. Tendons serve as a mechanical buffer for muscles, absorbing and storing energy from concussive forces. They also act like springs, swiftly releasing stored energy to power muscles and propel the leg forward. This mechanism helps to prevent wear-and-tear on the muscles. [1]

Tendons are resistant to tearing, but they are prone to injury because they lack stretching ability. Any forceful strain or awkward movement that pushes the tendon beyond its stretching limit can result in injury. [3]

Injured tendons are slow to heal because of a lack of blood supply to the area. While the body can regenerate connective tissues, they usually do not regain their original strength after an injury.

Fortunately, several treatments are available to help horses recover from a tendon injury, including non-invasive, newly developed treatments and surgical approaches. If your horse is affected by a tendon injury, consult your veterinarian to determine an individualized treatment plan.

Tendons of the Horse’s Legs

Tendons are critical for the horse’s ability to walk, run, jump, and perform various athletic activities. They play an important role in the horse’s limbs, transmitting forces generated by muscles to produce movement and provide stability to the skeletal system.

The tendons in a horse’s leg include the superficial digital flexor tendon (SDFT), deep digital flexor tendon (DDFT), and extensor tendons.

The superficial digital flexor tendon is located below the hock, or knee, and extends down the cannon to the pastern bone. It is responsible for flexing the digit and experiences high loading stress when the horse is in movement. This makes the SDFT susceptible to overstrain injuries. [3]

The deep digital flexor tendon runs along the back of the cannon bone in the leg, connecting the short pastern to the coffin bone in the hoof. The DDFT is very strong when compared to the SDFT and has high propulsion power. [4]

The extensor tendons run down the front of the cannon and pastern bones. They allow the horse to extend the fetlock in a forward movement. The extensor is not weight-supporting and is less likely to be injured than the flexor tendons. [5]

Signs of Injury

Most tendon injuries present with similar clinical signs, range from mild to severe depending on the extent and location of the injury.

Typical signs of a tendon injury include:

  • Swelling and heat in the back of the leg
  • Lameness (mild to severe)
  • Bulging or distension in the back of the leg
  • Sinking of the fetlock

Risk Factors for Tendon Injuries

Any horse can develop a tendon injury. However, certain management and training practices can put horses at higher risk of injury.

Some factors that can increase the risk of a tendon injury include: [3]

  • Poor foot balance (low heels, long toe)
  • Exercising on hard track surfaces
  • Muscle fatigue
  • Lameness in the opposite limb
  • Introducing heavy work in unconditioned horses
  • Excess weight (obesity, carrying heavy loads, etc.)
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Types of Tendon Injuries

The tendons in a horse’s legs are susceptible to different types of injuries. One common form is overstrain injuries, which occur due to repetitive micro-damage that gradually weakens the tendon over time.

In horses undergoing consistent training, tendons can lose their elasticity, strength, and ability to withstand high stress. Repetitive stress placed on a tendon can lead to disruption of collagen fibers and injury. [3]

Tendons can also suffer from acute injuries resulting from traumatic events. A significant impact or forceful event such as a fall or collision with a jumping pole can result in bruising or tearing of a tendon. Moreover, sharp objects can cause penetrating wounds that may sever the tendon and lead to infection.

Superficial Digital Flexor Tendon Injuries

The SDFT is highly prone to injury and one of the leading causes of lameness in racehorses. The SDFT in horses is the functional equivalent of the Achilles tendon in humans, and injuries to this tendon can take a year or longer to heal.

Up to 80% of horses with an SDFT injury experience re-injury, primarily due to the weaker scar tissue that forms to replace the damaged tendon. Between 19-70% of performance horses with an injured SDFT are retired from sports due to their injury. [6][7][8]

Injuries to the SDFT are more common in high-impact sports, including racing, eventing, jumping and polo. The most common injury to this tendon is tendonitis, otherwise known as a bowed tendon.

SDFT strains may result in core lesions that can be seen via ultrasound and excessive swelling. In acute injuries, this lesion is often accompanied by edema (fluid retention). [9][10]

Deep Digital Flexor Tendon Injuries

Injuries to the DDFT commonly occur in the pastern region rather than around the cannon bone. They can be recognized by the presence of fluid distension and swelling in the pastern area.

Overstrain injuries to the DDFT can cause persistent, low-grade lameness in horses. Deep digital flexor tendon damage is commonly seen in dressage and show-jumping horses. [10]

Treatment for DDFT injuries can involve  4-12 months of stall rest for the horse, along with physical rehabilitation. [11]

Extensor Tendon Injuries

Injuries to the extensor tendon in horses are infrequent due to its location on the body. Unlike the weight-bearing flexor tendons, the extensor tendon has less of an impact on performance and typically heals well without invasive treatment. [9]

Injury to the extensor tendon rarely affects the horse’s gait, although stumbling during walking may occur until the leg is healed. This can be mitigated through corrective hoof shoeing or trimming.

If a horse falls or strikes its lower leg, the extensor tendon can suffer lacerations. This trauma can lead to infection in the tendon sheath. [5]

Tendon Sheath Injury (Tenosynovitis)

Tenosynovitis is a condition that involves inflammation of the tendon sheath, usually occurring in response to trauma. It is common in working and performance horses and can cause varying degrees of swelling, lameness and pain. [12]

Tendons are surrounded by a protective layer called the tendon sheath, consisting of connective tissues that contain lubricating synovial fluid. The sheath protects the tendon from abrasion and wear, while facilitating smooth movement without friction or resistance. [2]

Tenosynovitis is characterized by swelling and distension of the tendon sheath in the lower leg. This results from the buildup of synovial fluid in the affected area, known as synovial effusion.

Tenosynovitis in horses can be classified into three primary types: acute, chronic, and septic. Acute and chronic cases typically stem from injury or trauma, while septic tenosynovitis occurs when the tendon is penetrated, leading to infection. [13]

Typical clinical signs of advanced septic tenosynovitis in horses include the following:

  • Reluctance to bear weight on the affected limb
  • Swollen tissues around the wound
  • Elevated temperature or fever
  • Depression

Septic tenosynovitis can result in significant swelling and lameness in the lower leg, requiring immediate medical intervention to address the infection. Early identification and treatment, ideally within 24 hours of symptom onset, significantly improve the prognosis for the horse. [14]

Diagnosis

Tendon injuries caused by strain are highly prevalent in equine sports, making this a relatively straightforward condition for your veterinarian to diagnose.

Typically, diagnosis relies on the horse’s training and health records, alongside identifying inflammation in the affected area. [9]

Physical Examination

Your veterinarian will perform a physical examination to assess the damage to the horse’s tendon. Horses with tendon injuries may not be lame, because lameness is more closely related to the degree of inflammation rather than the severity of the injury. As a result, lameness exams may not provide useful diagnostic information. [9]

Before palpating the injured area, your veterinarian will look for visual signs of swelling in the affected area. Mild tendon injuries with limited swelling may only be visible when the horse is clipped.

Palpating the tendon between the thumb and forefinger allows your veterinarian to feel for any subtle thickening indicative of an overstrain injury. Your veterinarian will assess the leg for abnormalities both while it is bearing weight and when it is not, to identify any potential issues.

Diagnostic Ultrasound

A common technique for diagnosing tendon injuries is ultrasonography. This cost-effective and non-invasive imaging technique employs high-frequency soundwaves to generate images that help identify tendon tears or other types of damage. [7]

Once a tear has been detected, ultrasound can be used to monitor the rehabilitation progress during treatment. Scheduling ultrasound evaluations at least every three months during the recovery period to ensure proper healing of the tendon is important.

Treatment for Tendon Injuries

Depending on the severity of the injury, tendon injuries in horses are usually treated with some combination of stall rest, supportive care and surgical intervention. Work with your veterinarian to determine the best treatment plan for your horse.

Similar to other types of wounds, the healing process for tendons involves an initial inflammatory phase, followed by a remodelling phase. The inflammatory phase typically lasts approximately 1-2 weeks, during which lameness and pain are commonly experienced.[9][15]

Following this period, swelling may go down rapidly as the tendon begins to heal. Not all tendon injuries follow this pattern, and some injuries can result in long-term, low-grade lameness.

Stall Rest

Stall rest is recommended to support tendon repair, reduce the risk of further injury, and prevent the horse from putting excess weight on the injured tissue. The ideal duration of stall rest varies based on the severity of the injury, intended use for the horse and veterinary assessment.

Generally, a horse with a flexor tendon injury will spend anywhere between 6 to 12 months on stall rest.

After the inflammation has subsided, horses with tendon injuries may resume controlled exercise at the discretion of a veterinarian. Gentle hand-walking for short durations (5-10 minutes) can help loosen tight muscles, reduce the risk of swelling, and prevent stocking up or stagnation edema during periods of stall rest. [16]

Cold Therapy

Cold therapy (cryotherapy) is beneficial during the inflammatory phase of a tendon injury to reduce swelling. Applying cold water or ice to the affected area promotes vasoconstriction (narrowing of blood vessels), reduced inflammation and pain relief. [9]

For maximum results, cold hydrotherapy should be conducted several times per day for 25 – 30 minutes or less. Prolonged exposure to cold should be avoided as it can lead to local freezing, tissue swelling and edema. [9]

Supportive Bandaging

Pressure bandages can help stabilize and support the tendon and prevent fluid accumulation. Typically, the leg is wrapped with a bandage for 3-4 weeks after the injury. It is recommended to change the bandage at least once daily.[3]

Proper technique is crucial when bandaging the tendon to ensure it is comfortable for the horse. Incorrect application of bandages can result in discomfort, failure to support the tendon or potentially exacerbate the injury. [17]

Medication

Non-steroidal anti-inflammatory drugs (NSAIDs) and corticosteroids are commonly prescribed medications following a tendon injury. These medications help reduce inflammation at the injury site and alleviate pain.

NSAIDs can help prevent unwanted tissue adhesion within the tendon during the healing process. Typically, a 3-5 day course of NSAIDs is recommended. Phenylbutazone, commonly known as Bute, is administered after an injury to reduce excessive inflammation that could impair the healing process. [18][3]

Systemic steroids can be administered within the first 24-48 hours after an injury to effectively decrease swelling and pain. It is important to discontinue their use beyond the inflammatory phase, as prolonged steroid use can inhibit fibroplasia (fibrous tissue repair), which is essential for proper tendon repair. [9]

Polysulfated glycosaminoglycans (PSGAGs) are injectable anti-inflammatory agents used to alleviate pain and promote the repair of connective tissue. While there is limited evidence on their use for tendon injuries, PSGAGs may offer benefits during the healing process.

They are believed to inhibit macrophage activation, collagenase, and inflammatory molecules while potentially stimulating tendon cells to produce collagen – a protein that constitutes more than 80% of tendon tissue. [10][7][3]

Stem Cell Therapy

Stem cells possess the ability to transform into different cell types, allowing them to replace damaged cells and support tissue repair. This makes stem cell therapy an increasingly popular treatment option in the equine industry; however, conclusive research showing the efficacy of this approach is limited.

Among the various types of stem cells, mesenchymal stem cells (MSCs) can be obtained from the horse’s bone marrow, body fat, blood, or tendons and subsequently injected into the injured tendon. [19] MSCs have the potential to differentiate into mature tendon cells (tenocytes) at the site of injury. They can also reduce inflammation and pain, speeding up the healing process. [9]

It is important to note that stem cell therapy can be costly, and there is no guarantee that it will work for your horse. If you are considering stem cell therapy as a treatment option for your horse’s tendon injury, discuss this treatment further with your veterinarian.

Platelet-Rich Plasma

Platelet-rich plasma (PRP) is a newly developed therapy for treating tendon and ligament injuries. It involves the injection of platelet-rich blood plasma derived from the horse’s body directly into the affected tendon. This technique aims to stimulate tissue repair and facilitate the healing process. [8][9]

PRP contains four times the amount of platelets as the horse’s normal blood. PRP also contains high levels of growth factors, which promote anabolic effects that may help with tissue repair.

PRP therapy enhances blood supply to the injured tendon, promoting tissue maturation and remodelling. This method is cost-effective and minimally invasive. When used alongside other treatments, it can shorten healing time.

Scaffolds

Scaffolds are specially designed materials that are injected into an injured tendon to assist with the formation of new tissue. [9].

Scaffolds work by carrying and attracting cells to the injury site, helping to align tissue structures, and protecting cells during the early stages of implantation before new tissue formation occurs. [9].

Among the new intralesional treatments for tendons, some use components derived from the submucosa of porcine urinary bladder (pig bladder tissue).

These components are injected into the injured tendon, delivering essential growth factors and attracting mesenchymal stem cells to expedite the healing process, enhance tissue integrity, and improve strength.

However, treatment sessions are associated with inflammation. Anti-inflammatory medication and cold therapy should be combined with scaffolds to minimize pain and swelling.

Hyaluronic Acid

Sodium hyaluronate (SH), or hyaluronic acid (HA), is a structural component of joint cartilage. It can be injected into injured tendons to support healing, inhibiting the inflammatory response and reducing adhesions.

Research on the efficacy of hyaluronic acid for tendon injuries is mixed. [7][9]

Shockwave Therapy

Extracorporeal Shockwave Therapy (ESWT) is a non-invasive treatment for tendon and ligament injuries. It involves applying high-frequency pressure waves to the skin to vibrate healing tissues and increase blood flow to the area. [20]

This procedure is usually performed once a week during the rehabilitation process and is generally considered safe for the horse. It can help reduce pain, improve nutrient delivery to cells and has the potential to accelerate healing.

However, the precise therapeutic mechanisms of this treatment are not fully understood, and it is commonly used with other treatment approaches to maximize effectiveness.

Surgical Treatments

Tendon Splitting

Percutaneous tendon splitting involves making small incisions into the swollen tendon to drain fluid and speed up recovery. This procedure can be performed under general anesthesia or standing sedation. [9]

Tendon splitting is no longer recommended for chronic tendinitis. While it was once thought to improve blood flow and oxygenation to the injury site, veterinarians now know it can cause significant trauma to healthy surrounding tissues and induce or worsen lameness.

This procedure may promote the formation of fragile granulation tissue at the injury site, which can make tendons prone to re-injury. However, tendon splitting can be effective for acute tendon injuries as it helps drain fluid and resolve core lesions.

After the procedure, the leg is wrapped with a bandage, and the horse is put on stall rest for 10 – 14 days. Controlled exercise is gradually reintroduced after the initial recovery period.

Superior Check Ligament Desmotomy

Superior Check Ligament Desmotomy (SCLD) is a minimally invasive surgery that aims to reduce strain on the injured SDFT by transecting and lengthening a portion of the accessory ligament. This reduces the weight-bearing load on the injured tendon. [9]

This surgery is conducted percutaneously (through the skin) while the horse is laying down or standing under anesthesia. The recovery period for this procedure is typically brief, involving stall rest and a short course of NSAIDs to alleviate pain.

Pin Firing

Pin firing, or counter irritation, is an outdated, invasive treatment for tendon injuries that was traditionally used in racehorses with chronic tendon injuries. It can be conducted under general anesthesia or standing sedation.

This treatment involves the application of chemicals or a hot probe to cauterize tissue above the lower leg injury. The procedure was formerly thought to promote the formation of scar tissue and strengthen the healing of the tendon. [21]

However, this method is now considered inhumane and its effectiveness remains uncertain. Due to the lack of scientific evidence, it is not recommended. [21]

Treatment for Tenosynovitis

Inflammation of the synovial membrane of the tendon sheath (tenosynovitis) is usually treated with non-invasive methods. Treatments include stall rest, bandaging the affected leg, regular cold therapy and administering NSAIDs. [13]

For horses with septic tenosynovitis, the most common treatment is a combination of local and systemic antimicrobials, lavage (flushing) of the infected area and drainage.

Tenoscopy, a surgical procedure that involves making small incisions in the skin, may be conducted to visualize and clean the tendon sheath. This procedure is conducted under general anesthesia and involves flushing the structures of the tendon with sterile fluid to remove foreign materials and debris. [13]

Nutritional Support

Nutrition plays an important role in supporting horses with tendon injuries. Key nutrients, including vitamins and minerals, are required in the diet to support the healing process and maintain healthy connective tissue.

Weight management is also important for horses recovering from a tendon or ligament injury. Horses with reduced activity levels require fewer calories in their diet to prevent excessive weight gain, which can place additional stress on healing tissues.

The following nutritional supplements can also be added to the diet to support tendon health in horses:

  • Amino acids: Lysine, methionine, and threonine are limiting amino acids required for protein synthesis. Adequate protein synthesis is vital for tissue repair and collagen formation.
  • Vitamin C: This nutrient plays a crucial role in supporting healthy connective tissue and collagen synthesis. [22]
  • Methylsolfonylmethane (MSM): MSM is a bioavailable source of sulfur that helps maintain healthy connective tissue and can support horses recovering from tendon injuries. It is commonly used as a joint supplement.
  • Omega-3 Fatty Acids: Supplementing the horse’s diet with omega-3 fatty acids, such as DHA, can help regulate inflammatory processes in the body, potentially reducing inflammation during the recovery period.

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By providing a well-balanced diet, including essential nutrients, the horse’s body can better support tendon health and tissue repair processes. Submit your horse’s diet online for free evaluation by our qualified equine nutritionists.

Prognosis

The prognosis for horses with tendon injuries depends on the location and severity of the injury and the duration and quality of rehabilitation. Outcomes vary greatly between individual horses.

In horses with flexor tendon injuries, some are able to return to their previous work, but re-injury is extremely common. Horses that undergo less than 6 months of stall rest have a significantly higher risk of reinjury. [7]

Extensor tendon injuries generally have a good prognosis, with approximately 72-80% of horses successfully returning to sports following healing. When it comes to septic and chronic tenosynovitis in the extensor tendon, prompt treatment significantly improves the prognosis.

If you suspect that your horse has sustained a tendon injury, contact your veterinarian for a thorough physical evaluation. Early diagnosis and appropriate treatment are key to ensuring the best possible outcome for your horse.

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References

  1. Roberts, T. J. and Konow, N. How tendons buffer energy dissipation by muscle. Exerc Sport Sci Rev. 2014.
  2. What are tendons and tendon sheaths?. Institute for Quality and Efficiency in Health Care (IQWiG). 2018.
  3. O’Sullivan, C. B. Injuries of the Flexor Tendons: Focus on the Superficial Digital Flexor Tendon. Clin Tech Equine Pract. 2007.
  4. Luard, L. D. The Anatomy and Action of the Horse. Dover Publications, INC. 2003.
  5. Booth, T. M. et al. Resection of the common digital extensor tendon in a gelding. Vet Rec. 2000. View Summary
  6. Patterson-Kane, J. C. The Pathogensis of Tendon Microdamage in Athletes: the Horse as Natural Model for Basic Cellular Research. J Comp Pathol. 2012.
  7. Dowling, B. A. et al. Superficial digital flexor tendonitis in the horse. Equine Vet J. 2000. View Summary
  8. Fortier, L. A. & Smith, R. K. W. Regenerative medicine for tendinous and ligamentous injuries of sport horses. Vet Clin North Am Equine Pract. 2008. View Summary
  9. Smith, R. K. W. Tendon and Ligament Injury. American Association of Equine Practitioners (AAEP) . 2008.
  10. Barrett, J. & White, N. A. Introducion to Equine Tendon Injury. American Association of Equine Practitioners (AAEP). 2008.
  11. Lutter, J. D. et al. Medical treatment of horses with deep digital flexor tendon injuries diagnosed with high-field-strength magnetic resonance imaging: 118 cases (2000-2010). J Am Vet Med Assoc. 2015.
  12. Brokken, M. T. Digital Sheath Tenosynovitis in Horses. Merck Veterinary Manual. 2015.
  13. Adams, S. B. Disorders of Tendon in Animals. Merck Veterinary Manual. 2020.
  14. Ludwig, E. K. Equine Wounds over Synovial Structures. Vet Clin North Am Equine Pract. 2018. View Summary
  15. Thomopoulos, S. et al. Mechanisms of tendon injury and repair. J Orthop Res. 2015.
  16. Tips for Managing Horses on Stall Rest. Kentucky Equine Research. 2018. View Summary
  17. Denney-Jones, E. Wound Management & Bandaging. American Association of Equine Practitioners (AAEP). 2006.
  18. O’Brien, C. et al. Microdamage in the equine superficial digital flexor tendon. Equine Vet J. 2020. View Summary
  19. Schnabel, L. V. et al. Therapeutic use of stem cells in horses: Which type, how, and when?. Vet J. 2013. View Summary
  20. Shockwave Therpy for Tendon Injuries in Horses: The Good and the Bad. Kentucky Equine Research. 2013.
  21. Hayward, M. & Adams, D. The firing of horses. 2001.
  22. Tack, C. et al. The Physiological Mechanisms of Effect of Vitamins and Amino Acids on Tendon and Muscle Healing: A Systematic Review. Int J Sport Nutr Exerc Metab. 2018.