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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]
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.
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