Bowed tendon in horses is defined as acute or chronic inflammation of a tendon. This condition is also known as tendinitis, tendonitis or tendinopathy.

This injury usually occurs when the tendon is strained beyond its limit, resulting in torn collagen fibers. [13] Tendinitis affects the digital flexor tendons in the lower leg of the horse and can cause severe swelling, pain and lameness.

Racehorses and performance horses are more likely to be affected due to the intensity of their sports. Between 8-43% of racing Thoroughbreds develop a bowed tendon during their racing career. However, any horse can develop tendinitis. [6]

There are several treatments available for bowed tendons, including stall rest, anti-inflammatory medication, physical therapy, holistic treatment and gradual return to exercise. Some cases may require ongoing treatment or surgical intervention.

If you think your horse could have a bowed tendon, contact your veterinarian immediately for diagnosis and to develop a treatment plan tailored to your horse.

Equine Tendon Structure & Function

Tendons are fibrous and dense connective tissues that attach the end of a muscle to a bone. They are extremely important for absorbing impact in the horse’s legs and preventing muscle injury.

When a muscle contracts, the tendon extends and transmits the force of the contraction to the bone, allowing movement in the limb.

Tendons consist predominantly of proteinaceous collagen fibres forming a cable-like structure with collagen arranged in fibril bundles. [21][6]

This structural arrangement allows for high tensile strength, which describes the tendon’s ability to withstand extreme force and pressure without snapping.

Tendons are situated within a lubricated sheath, allowing the tendon to move without resistance or friction and protecting the tendon from abrasion and damage.

Superficial Digital Flexor Tendon

The superficial digital flexor tendon (SDFT) is an energy-storing tendon found at the back of the horse’s leg, between the short pastern and coffin bone. It is responsible for stabilizing the fetlock joint and is highly susceptible to injury. [14]

Repeated loading of the tendon without adequate rest in between exercise bouts increases the likelihood of failure  Between 75-95% of tendon injuries in the horse occur in the SDFL of the forelimb.

The Deep Digital Flexor Tendon

The deep digital flexor tendon (DDFT) is the other flexor tendon, which can be found in the back of the horse’s leg. It helps stabilize the joints in the lower leg when bearing weight, as well as support flexion of the hoof.

A bowed DDFT is very uncommon compared to a bowed SDFT. The majority of injuries to this tendon occur within the horse’s hoof capsule, behind the fetlock or in the pastern region. [18]

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Clinical Signs of Bowed Tendons

Tendons are capable of only minimal elongation, and these fibers can tear under extreme, sudden or consistent stress. Tendon tears can vary in severity, with some causing significant swelling and pain in the horse’s lower leg. The majority of equine tendon injuries occur in the forelegs.

Some horses develop a bowed tendon from a sudden injury, such as tripping or stepping in a hole. Horses in heavy training or performance sports can develop a bowed tendon from everyday wear and tear.

Acute Bowed Tendon

In acute cases, a horse with a bowed tendon will have a prominent curved, bow-like swelling on the back of the leg in the cannon bone region. The affected area is usually very painful, hot to the touch and swollen following injury.

The bow commonly occurs in the center of the tendon but can also form right below the knee (a high bow), right above the fetlock (low bow). Some bows can affect all three sites. In some cases, a bow is only visible once the leg hair has been clipped. [18]

Lameness associated with an SDFT injury can be mild and resolve quickly over the week following the initial injury. The grade of lameness rarely correlates with the severity of the injury, except in severe cases.

Overstrain injuries to the DDFT can result in low-grade, persistent lameness and lesions on the suspensory ligament in the hindlimb, otherwise known as suspensory ligament (SL) desmitis. [18]

Chronic Tendinitis

In chronic cases of tendinitis, there can be thickening of the injured tissue and adhesions in the area surrounding the tendons. Affected horses may be sound at a walk and trot but lame under heavier, concussive work. [12]

Lameness can be severe after an injury but often improves within two weeks following the inflammatory phase. While the horse may seem recovered, the injury is still present and can remain long-term, so careful management throughout the entire healing period is necessary.

Risk Factors

Horses in fast, high-intensity work have an increased risk of a bowed tendon. Individual factors, such as age, sex, breed, flexibility and strength, can contribute to recovery rates and severity of the injury. [14]

Several factors may predispose a horse to a bowed tendon or chronic tendinitis, including;

  • Conformational abnormalities
  • Poor surface or track conditions
  • Fatigue
  • Direct trauma to the lower leg
  • Improper bandaging
  • Improper hoof trimming
  • Primary tendon degeneration
  • Lack of blood flow to the tendon (ischemia)

Prevention

To prevent the development of a bowed tendon or chronic tendinitis, it is important to maintain your horse’s fitness. Some tendon and ligament injuries can be avoided by improving stamina and strength.

Implementing a cross-training regime can improve your horse’s coordination and teach them to pick up their feet while in motion. Cross-training can also improve balance and prevent the wear and tear associated with a constant heavy workload.

It is essential that horses have regular farrier work and properly fitted shoes or appropriate barefoot trimming to prevent imbalances and tendon damage. [10]

Diagnosis

In order to diagnose a horse with a bowed tendon, your veterinarian will carefully palpate the affected tendon between the thumb and forefinger while it’s bearing weight and while it is slack. This method allows any thickening of tissue to be identified. [15]

Palpation can help identify some swelling and damage in the tendon, although it does not show the veterinarian the extent of the damage.

Ultrasound

A diagnostic ultrasound should be conducted to determine the integrity and alignment of the tendon fibers and collagen. Ultrasonography is helpful for diagnosing injuries that are not visible to the eye. [10]

This ultrasound is usually scheduled 5 – 10 days following the injury, as this is when tendon damage will be most apparent. A healthy tendon appears stark white on an ultrasound, whereas a damaged tendon appears gray or black.

Throughout treatment and rehabilitation, an ultrasound of the affected tendon should be conducted at least every 2-3 months. This will help the veterinarian evaluate the progress of the treatment plan and decide how much exercise the horse should be receiving. [6][18]

Treatment

Bowed tendons respond best to prompt treatment in the early, acute stage. Once a horse has been diagnosed with a tendon injury, a rehabilitation plan must be put in place to ensure a successful recovery. [13]

Many treatment methods and procedures are used in combination to reduce symptoms and facilitate recovery. Your veterinarian will individualize a treatment plan appropriate for your horse.

Physical Therapy

Horses with tendon inflammation should receive cold therapy several times a day for at least five days to reduce swelling. Immediate soaking of the leg with cold water following injury will minimize swelling. [9][15]

Regularly soaking or hosing the injured leg with cold water or applying ice for 5-10 minutes at a time can help reduce acute inflammation. Hydrotherapy with cold water is recommended as it is more efficient and safer than holding ice to the injured leg. [19]

Stall rest

Most horses with tendinitis require long-term stall rest for several months to a year, depending on the severity of the injury. [10][13]

Stall rest is usually required before the horse can demonstrate full athletic potential. This allows the horse to heal while preventing re-injury. [18]

Stall rest is inherently stressful for horses due to movement restriction and social isolation. Pay extra attention to a horse’s diet during this time to support well-being and digestive function.

Horses should have ad libitum access to forage while stalled to reduce boredom as well as decrease the risk of colic and gastric ulcers. Every horse handles stall rest differently, so it is important to work alongside your veterinarian and an equine nutritionist to ensure a healthy recovery.

Pressure bandaging

A pressure bandage can help stabilize the tendons in the leg as well as minimize swelling and bleeding prior to diagnosis and throughout treatment. Careful application is required, as improper bandaging can worsen the injury.

A bowed tendon should be iced or hosed down a few minutes before bandaging, and any open wounds should be sterilized to reduce the risk of infection.

A pressure bandage is made up of a soft layer (such as roll cotton, leg quilts, etc.) held in place by an external “pressure” layer (such as polo wraps or bandaging tape). This bandage should provide a tourniquet effect without cutting off the blood supply to the leg.

If the horse becomes more lame on that leg or swelling occurs above the bandage, it may be too tight. Note that improper bandaging can do more harm than good.

If you are unsure of how to apply a pressure bandage, ask your veterinarian to demonstrate the technique. [1]

Medication

Several analgesics (pain-relieving) and anti-inflammatory medications are available that can support horses recovering from a bowed tendon. Combining local and systemic anti-inflammatory treatment can promote healing and reduce pain.

Non-steroidal anti-inflammatory drugs (NSAIDs) can be administered immediately after injury to reduce inflammation and relieve pain. While inflammatory processes are important for healing, reducing the severity of inflammation can help protect the tissues and collagen surrounding the injury. [9]

Phenylbutazone, or Bute, is an NSAID that is commonly used to treat acute cases of tendinitis. NSAIDs should only be used short-term and at appropriate dosages, as excessive use can compromise the gastrointestinal tract and lead to ulcer formation.

Corticosteroids are powerful anti-inflammatory drugs that can be administered systemically or locally to reduce symptoms of acute tendinitis. Unfortunately, corticosteroids can inhibit important repair processes, such as the development of fibrous tissue and collagen synthesis.

Always talk to your veterinarian before administering medication for an injury and follow dosage guidelines provided based on your horse’s body weight.

Hyaluronic acid

Sodium hyaluronate, or hyaluronic acid (HA), is an important structural compound of joint cartilage and other tissues naturally found in the horse’s body.

Hyaluronic acid helps maintain joint health by inhibiting inflammatory responses. It may also support repair and prevent adhesion. [9]

HA can increase the reproduction and differentiation of cells in affected tissue as well as enhance cell migration to the injury for repair. This promotes faster healing, speeds up tissue maturation and prevents the tissue from thickening (otherwise known as fibrosis).

Injecting the tendon with hyaluronic acid (HA) can help ease pain and support repair processes following an acute bowed tendon. The treatment should be administered soon after the injury occurs for the best effect.

Exercise Rehabilitation

Once the initial inflammation subsides, it is important to safely re-introduce low-intensity exercise to the horse’s routine. If the injury is severe and the fetlock lacks support, exercise should be delayed to prevent further damage. [15]

A personalized exercise routine should be designed as part of the rehabilitation plan. The training schedule and exercises followed should be determined based on the severity of the horse’s injury, as well as the results from regular ultrasound check-ups.

In general, horses can begin hand-walking once the inflammation has subsided, anywhere between 1-3 weeks after the initial injury. Trotting can be reintroduced around three months, while cantering should be prevented until 7-8 months into rehabilitation.

Horses may be reintroduced to race training after eight months to 1 year of controlled exercise rehabilitation.

Newly Developed Treatment Methods

Various new treatments available for tendinitis have demonstrated variable efficacy in horses. These methods show some promise in the treatment of bowed tendons, but more research is needed.

Stem Cells & Platelet-rich Plasma

Stem cell therapy may be a viable option for mending an injured tendon in horses. This treatment involves injecting the tendon with mesenchymal stem cells (MSCs), which are found in bone marrow, body fat, blood or tendons. [5]

Evidence suggests these cells can promote tissue regeneration, improving the rate and quality of tendon healing, as well as may help to prevent re-injury.

Platelet-rich Plasma (PRP) involves injecting a high concentration of platelets from the horse’s blood into its own tendon. This is thought to accelerate healing. This method of treatment is minimally invasive, efficient and relatively low in cost.

Studies show that PRP improves vascularization (blood supply) and metabolic activity in the tendon, which promotes tissue maturation, collagen synthesis and tendon remodelling. This strengthens the tendon and helps prevent re-injury.

Horses treated with cell therapy demonstrate a significantly lower re-injury rate (27%) than those treated with traditional methods (56%). However, further research is needed before stem cell injection and PRP becomes standard practice for treating bowed tendons and chronic tendinitis. [5]

Shock Wave Therapy

Extracorporeal shock wave therapy (ESWT) is a potential non-invasive treatment for tendinitis, as well as other musculoskeletal injuries and disorders. It involves applying high-amplitude pressure waves on parts of the body to increase blood flow to the area. [11]

The exact therapeutic mechanisms behind ESWT are unknown. It is thought that these shockwaves stimulate tissue regeneration by causing interstitial responses and micro-tears in the area.

Likely, several different mechanisms work together during ESWT to contribute to the horse’s regenerative processes. [17]

High-Intensity Laser Therapy

Research shows that stimulating tendon injuries with a high-power infrared laser can activate processes involved in tissue healing. This type of laser therapy promotes anti-inflammatory and analgesic effects, also helping to prevent edema or swelling caused by trapped fluid. [22]

While high-intensity laser therapy (HILT) has not been studied in depth in veterinary medicine, it may be beneficial as an adjunct therapy when combined with other treatments.

A single treatment session lasts around 30 minutes and is usually conducted daily for a period of two weeks. [13]

Acupuncture

Acupuncture is a traditional medicine practice that involves strategically inserting thin needles through the skin at specific points in the body. This treatment is thought to stimulate the nervous system to achieve a pain-relieving effect and return the body to homeostasis. [8]

When conducted by a qualified practitioner, acupuncture is safe for horses and can be administered with minimal risk of adverse effects. This makes it a highly sought-after treatment for many health conditions and illnesses.

A single session takes approximately 20-60 minutes, and several sessions are usually needed to see results. Acupuncture is often used in conjunction with traditional treatments to reduce symptoms from a bowed tendon or chronic tendinitis. [16]

Therapeutic Ultrasound

Therapeutic ultrasound is a type of physical therapy for equine injuries that is non-invasive, safe and may improve animal comfort. While your veterinarian performs diagnostic ultrasounds, therapeutic ultrasound is usually conducted by a physical therapist.

This method involves applying pulses of heat and energy to the injured area. The ultrasonic waves are absorbed by collagen-rich tissues, including tendons and ligaments. This promotes tissue healing, increases blood flow and reduces inflammation in the area. [4]

Short-term use of therapeutic ultrasound is not likely to improve tendon repair. However, limited research shows that this form of ultrasound may be beneficial if used long-term during the healing process. More research is needed to evaluate the efficacy of this treatment modality. [4]

Magnetic Therapy

Magnetic therapy is thought to help the body heal by increasing blood flow and oxygen delivery to the affected area, reducing inflammation. [20]

Pulsed electromagnetic field therapy (PEMF) products, in the form of boots or blankets, are commercially available and are purported to have benefits for:

  • Soft-tissue & muscle injuries
  • Stiffness & inflammation in the body
  • Arthritis & osteoporosis
  • Hoof conditions (i.e. laminitis)

These products emit variable electric impulses directed at the body to create a magnetic field. This is thought to relieve inflammation by accelerating metabolic processes at the cellular level and increasing circulation.

Anecdotally, magnetic products can be helpful for promoting healing in some parts of the body. However, research suggests that PEMF therapy has little effect on tendon repair in horses. [20]

Magnetic therapy is usually applied in conjunction with other treatments, such as physical therapy and medication. It can also be used as a preventative measure for injuries.

Surgical Treatment Methods

Some horses with severe tendon injuries or poor prognoses require surgical intervention. Most tendon injuries eventually heal without surgery. However, re-injury is more common in these cases. [2]

Research shows that horses undergoing surgical treatment for a tendon injury are 4.7 times more likely to return to performance sports than horses with injuries that are managed by medical intervention alone.

Superior Check Ligament Desmotomy (SCLD)

A superior check ligament desmotomy (SCLD) can be conducted to reduce tension on the healing superficial digital flexor tendon (SDFT). This surgery involves transecting and lengthening the accessory ligament of the SDFT, reducing the weight load on the tendon. [2][18]

This surgery can be conducted with a percutaneous approach (through the skin) while the horse is lying down or standing under anesthesia. There is also an endoscopic SCLD method through the carpal sheath, which is the area that extends from the knee to the middle of the cannon region.

Tendon Splitting

Percutaneous tendon splitting involves making small incisions into the damaged tendon to drain fluid and speed up recovery.

Tendon splitting was thought to improve vascularization or the formation of blood vessels in the tissue. Increased vascularization improves nutrient and oxygen supply to the tendon and facilitates tissue repair. However, this theory has since been disproven. [6]

Tendon splitting should be considered early on in treatment. Splitting later in the repair process can cause excess trauma to the tendon, result in scar tissue growth and worsen lameness. This procedure has no effect on collagen production. [9]

The quality of repair and rehabilitation following tendon splitting varies between individuals. Other less-invasive methods of treatment are usually attempted before considering tendon splitting as a treatment.

Pin Firing

Pin firing, or counter irritation, is an outdated method of treating tendon and ligament injuries. It consists of using chemicals or a hot probe to cauterize tissue on the lower legs of horses with chronic injuries such as tendinitis. It is performed under general anesthesia or standing sedation. [18]

Pin firing was thought to toughen up the leg and was traditionally used on racehorses. It is now considered cruel as a form of treatment and is not recommended due to a lack of scientific evidence. [3]

Nutritional Support

You can support your horse’s recovery from a tendon injury by feeding a balanced diet, ensuring your horse is at a healthy weight and providing nutritional supplements to support connective tissues.

Weight management is particularly important for horses on stall rest coming back to work. Horses that are carrying too much body condition experience increased loads on their connective tissue, including joints, tendons and ligaments.

Work with a qualified nutritionist to design a feeding program for your horse that supports tendon repair. Your horse’s ration will need to be adjusted to reflect changes in activity as they go from stall rest to light exercise.

Macronutrients & Micronutrients

Equine diets that are deficient in vitamins, minerals and amino acids can slow down the recovery from a soft-tissue injury.

Vitamin and minerals play important roles in metabolic processes that support tissue repair for horses with bowed tendons.

Some of the key nutrients required to support healthy connective tissue include:

  • Vitamins A, C and E [23][24]
  • Macro minerals sulfur and magnesium [25][26]
  • Trace minerals zinc, copper, manganese and cobalt [27]

Amino acids are the building blocks of protein and are required in the diet to support collagen formation. While horses typically get adequate protein in their diet, not all rations provide a balanced profile of amino acids.

Lysine, methionine and threonine are the three most limiting amino acids in the equine diet. Deficiencies in these nutrients are the most likely to slow down the rate of protein synthesis in the horse’s body.

To address dietary deficiencies, feed a balanced nutritional supplement, such as Mad Barn’s Omneity. Omneity provides vitamins, minerals and amino acids required to balance the equine diet and supports healthy tendons and connective tissues.

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MSM (Methylsulfonylmethane)

MSM is a bioavailable source of the mineral sulfur, which has been shown to help maintain healthy connective tissue, cartilage and bones in horses. [7]

MSM can be given to horses as a joint supplement to support collagen and cartilage in the body. It can also benefit horses recovering from musculoskeletal injuries.

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Omega-3 Fatty Acids

DHA is an omega-3 fatty acid that helps to maintain the normal regulation of inflammatory processes in the body. Feeding DHA to a horse with a bowed tendon may help to decrease the inflammatory response following injury.

In one study, DHA was shown to reduce inflammation and improve lameness scores in horses with experimentally-induced joint inflammation. [28]

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Prognosis

The prognosis for a horse with a bowed tendon depends on the severity of the initial injury and the degree of appropriate supportive care or surgical intervention. [15]

Horses with severe tendon injuries may not be able to return to their previous level of work, as healed tendons can remain weak. It is estimated that 80% of Thoroughbred racehorses that return to racing sustain a re-injury.

Horses should be rested for a minimum of six months to prevent re-injury and a worsening outcome. Many horses that recover from a bowed tendon sustain injuries in their opposite limb.

If your horse sustains a tendon injury, put a rehabilitation plan in place immediately with the help of your veterinarian. Prompt medical intervention and regular supervision from a veterinarian will positively improve a horse’s prognosis.

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References

  1. Applying Pressure Bandages. American Association of Equine Practitioners (AAEP).
  2. Surgical Success for Horses with Tendon Injuries. Kentucky Equine Research. 2022.
  3. The Code of Practice for the Care and Handling of Equines. National Farm Animal Care Council. 2018.
  4. Brooks, J.The Use of Therapeutic Ultrasound for Equine Injuries. Animal Rehabilitation. 2011.
  5. Carvahlo, A. M. et al. Equine tendonitis therapy using mesenchymal stem cells and platelet concentrates. Stem Cell Research & Therapy. 2013. View Summary
  6. Dowling, B. A. et al. Superficial digital flexor tendonitis in the horse. Equine Vet J. 2010. View Summary
  7. Equimed Staff. Methylsulfonylmethane. Equimed. 2014.
  8. Gülanburger, E. G. et al. The Clinical Effectiveness and Application of Veterinary Acupuncture. AJTCVM. 2008.
  9. Henninger, R. Treatment of superficial digital flexor tendinitis in the horse. Equine Vet Educ. 1992.
  10. Lewis, M. L. Healing the Bowed Tendon. American Association of Equine Practitioners (AAEP). n.d.
  11. McClure, S. R. Extracorporwal Shock Wave Therapy in Horses: What we Know. American Association of Equine Practitioners (AAEP). 2016.
  12. Mcilwraith, C. W. Tendinitis in Horses. Merck Veterinary Manual. 2015.
  13. McKibbin, L. S. A Study of the Effects of Lasering on Chronic Bowed Tendons at Wheatley Hall Farm Limited, Canada, January, 1983. Lasers in Surgery and Medicine. 1983.View Summary
  14. O’Brien, C. et al. Microdamage in the equine superficial digital flexor tendon. Equine Vet J. 2020. View Summary
  15. O’Sullivan, C. B. Injuries of the Flexor Tendons: Focus on the Superficial Digital Flexor Tendon. Clin Tech Equine Pract. 2007.
  16. Schoen, A. Applying Acupuncture to Lameness in the Horse. American Association of Equine Practitioners (AAEP). 2016.
  17. Simplicio, C. L. et al. Extracorporeal shock wave therapy mechanisms in musculoskeletal regenerative medicine. J Clin Orthop Trauma. 2020.
  18. Smith, R. K. W. Tendon and Ligament Injury. American Association of Equine Practitioners (AAEP). 2008.
  19. Smith, R. & Schramme, M. Tendon injury in the horse: Current theories and therapies. In Practice. 2003.
  20. Steyn, P. F. et al. Effect of a static magnetic field on blood flow to the metacarpus in horses. J Am Vet Med Assoc. 2000. View Summary
  21. Villa-Forte, A. Tendons and Bursae. Merck Veterinary Manual. 2022.
  22. Zielińska, P. et al. Effects of High Intensity Laser Therapy in the Treatment of Tendon and Ligament Injuries in Performance Horses. Animals. 2020. View Summary
  23. Oakes, B. et al. Vitamin C in orthopedic practices: Current concepts, novel ideas, and future perspectives. J Orthop Res. 2021.
  24. Tack C, Shorthouse F, Kass L. 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.
  25. Maranon G. et al. The effect of methyl sulphonyl methane supplementation on biomarkers of oxidative stress in sport horses following jumping exercise. Acta Vet Scand. 2008. View Summary
  26. Wang, J. et al. Biodegradable Magnesium Screws Accelerate Fibrous Tissue Mineralization at the Tendon-Bone Insertion in Anterior Cruciate Ligament Reconstruction Model of Rabbit. Sci Rep. 2017.
  27. Dickson, Emily C. Effect of Complexed Trace Mineral Supplementation on Joint Health in Young, Exercising Horses. Texas A&M Univ Lib. 2018.
  28. Brennan, KM. et al. The effect of dietary microalgae on American Association of Equine Practitioners lameness scores and whole blood cytokine gene expression following a lipopolysaccharide challenge in mature horses. J Anim Sci. 2017.