Tendon injuries, as one of the most common orthopedic disorders, are a major cause of early retirement or wastage among sport horses.
The question: “Can a horse recover from a tendon injury?” is not easily answered since each injury is exacerbated by other factors, such as damage to surrounding structures, the age of the horse, and the current health of the horse.
In humans, tendon repair takes a long time and is often a painful process because it requires multiple healing modalities and a sustained resting period. Although frustrating, humans can take time off from exercise to stay off their feet and let nature and medicine take their course. Not so easy with horses.
Horses stand as a matter of survival and their need to keep moving around is fundamental to their functioning. This makes it very difficult (but not impossible) for a horse to recover from something like a total tendon rupture.
In this article, we examine why recovery from a tendon injury is difficult by looking at key structures in the leg and how injury to these areas can impair healing. Next, we will examine common tendon injuries and answer the question: How long does it take for a horse to recover from a tendon injury?
By the end of the article, you will understand the dynamics involved in tendon injury, which will help you make a well-informed decision about your horse’s health.
Let’s begin with the key structures affected by a tendon injury.
Key structures involved in horse tendon injuries
Source: Horseandhound.co.uk
Extensor and flexor tendons
Tendons are bands of fibrous connective tissues that connect muscles to bones, enabling movement. Tendons have remarkably high tensile strength for soft tissue. Their great strength is due to the impressive anatomical structure and tissue composition of the tendon fibers that contain many collagen fibers running in parallel orientations. In horses, the tendons in the lower leg are:
- Front of the leg: Extensor tendon
- Back of the leg: Superficial digital flexor tendon
- Back of the leg between the canon, suspensory ligament and the SDFT: Deep digital flexor tendon
In horses, the most common tendon injuries are the superficial digital flexor tendon (SDFT) and deep digital flexor tendon (DDFT), which we will discuss later.
Tendon Sheath
The tendon sheath is a fluid-filled protective covering that surrounds certain tendons, particularly those that run through areas where there’s a lot of movement or friction, like the joints in a horse’s legs. It’s lined with a synovial membrane that produces synovial fluid, which lubricates the tendon, reducing friction during movement.
Healing affected by an inflammatory response
When the tendon sheath is injured, it often leads to inflammation, hindering the healing process. This inflammation can increase the production of synovial fluid, leading to swelling and further complicating the injury.
Healing affected by adhesions
Adhesions are bands of scar tissue that can form between the tendon and its sheath. During the healing process, the body lays down collagen fibers to repair the damage. However, these fibers can sometimes adhere to the tendon and its sheath, essentially sticking them together.
These adhesions can restrict the smooth gliding motion of the tendon within the sheath, leading to stiffness, pain, and limited mobility. This can severely impact a horse’s performance and comfort. Injuries involving tendon sheaths are very serious, as infection in these structures is potentially life-threatening.
Collagen Fibers
Tendons are primarily composed of collagen fibers, which provide strength and flexibility to the tendon. Injuries involve the tearing and disruption of these fibers.
Healing affected by scar tissue
A damaged tendon heals through the production of scar tissue, which is very different from healthy collagen fibers. Scar tissue is less elastic than a healthy tendon because it forms in an unorganized manner and, therefore, is weaker, making re-injury more common. Re-injury occurs because the biomechanics of the tendon is affected.
To understand this, imagine a raw piece of steak that is soft and easily gives way under pressure when you press it. Now imagine a well-cooked piece of steak. It is harder and more fibrous, and even if you press into it, it does not bounce back easily. This is what an injured tendon with muscle involvement looks like.
Blood supply
One component that makes healing slow and difficult is that tendons have little blood supply. This means a lack of nutrients and oxygen needed for the repair of the injury site.
Surrounding muscle and bones
A significant tendon injury will involve the muscles and bones connected to it. If there is muscle atrophy due to lack of proper exercise, this can cause or exacerbate a tendon injury. Bones can be splintered or cracked depending on how the tendon snaps or breaks free from the bone.
Healing affected by damage to muscles
With a tendon injury, the muscle is used less due to pain and swelling, which can cause muscle atrophy, causing a vicious cycle to occur. Muscle atrophy doesn’t support the injured tendon as well as it should and further damage to the tendon results. Furthermore, the horse may compensate for the pain by overusing other muscles and causing a secondary injury in these areas.
Chemipower, in conjunction with Tartu University scientists, has undertaken extensive research into the natural compound carnosine for its effect on muscle recovery and decreased downtime due to its anti-inflammatory effects. As a supportive therapy, Carnogel works on muscles, tendons, and ligaments by providing the natural building blocks needed to maintain healthy, functioning limbs.
Healing affected by damage to bones
As injuries to tendons often cause secondary problems with the surrounding muscles and bones, your horse can experience increased pain and inflammation from stress fractures and cracks as a result of a weakened tendon.
Complex injuries involving several limb structures, such as an injured tendon, splintered bone, and suspensory ligament injury, are difficult to heal, and even if the horse owner is committed to recovery, the vet may recommend putting the horse to sleep.
Synovial membrane
Lines the tendon sheath and provides lubrication. Damage to the tendon can disrupt this membrane and thus affect the lubrication of the tendons and joints, making movement painful.
Healing affected by damage to the synovial membrane
Damage to the synovial membrane often triggers inflammation, leading to synovitis (inflammation of the synovial membrane) or tenosynovitis (inflammation of the tendon sheath). Since the synovial membrane provides the lubricating fluid for tendon health, any damage will cause difficulty in movement, making the horse uncomfortable and unable to resume normal activities.
Having examined the structures of the leg affected by a tendon injury and the different ways that healing is affected by these structures, let us now move on to two of the most common tendon injuries, namely, superficial digital flexor tendon injury (SDFT) and digital flexor tendon injury (DFT).
The Anatomy of Tendon Injuries in Horses
Superficial Digital Flexor Tendon Injury
The SDFT in the forelimb stores energy and is particularly prone to injury during high-impact activities like galloping and jumping, making it one of the most frequently cited reasons for lameness in performance horses.
These tendons are firm, owing to the impressive tissue composition and anatomical structure of the equine tendon fibers. There are also many collagen fibers present in the area in parallel orientations. These tendons also enable movements by passing on the force of muscle contraction to the bones.
Why is the SDFT most at risk?
The superficial digital flexor tendon is responsible for the stabilization and support of the fetlock joint. A 600kg racehorse impacts the ground with tremendous force during a gallop where one leg hits the ground at a time. A great deal of weight is supported by this very small cross-sectional area of flexor tendons, which is vulnerable to injuries.
Variations in training frequency, training intensity, training effects, surfaces, and equipment have also been identified as potential risk factors for SDFT injury. [1] This injury can happen suddenly resulting from a fall or a strike from another limb or gradually from being overworked, which can progressively weaken the tendon.
Signs of tendon injury include:
- Heat
- Pain upon touch
- Lameness within two to three days following the injury
- Swelling behind the cannon bone, and
- Refusal to switch leads
Deep Digital Flexor Tendon Injury
The deep digital flexor tendon (DDFT) arises from three locations in the upper forelimb: the humerus, radius, and ulna. It then courses down the carpal canal (the depression running down the back of the knee) and crosses over the navicular bone before inserting at the back of the coffin bone, lying deep beneath the SDFT and just over the suspensory ligament.
Horse tendon injury occurs most frequently within the hoof capsule and the sheath around the tendon, likely from repetitive, excessive loading. Usually, lesions appear in the body or borders of the tendon at the fetlock joint level and are more common in the hind than forelimbs.
The four most common DDFT lesions are:
- Tendon enlargements or changes in shape
- Focal core lesions
- Mineralizations
- Marginal tears
The prognosis for recovery from a tendon injury
Unfortunately, complete repair does not occur [2] because scar tissue that forms during the healing phase results in material properties inferior to the normal tendon tissue. This inadequate tissue healing causes a high risk of re-injury [3].
Up to 67% of horses experience relapse within 2 years of the original injury. However, after rehabilitation, horses can return to running activities even if they can no longer compete in professional racing sports. Numerous owners and trainers of performance horses regard tendon injuries as potentially more threatening to an equine athlete’s future career than fractures [4].
Conclusion
In conclusion, tendon injuries in horses present a significant challenge, not only due to the complex structure of the tendons themselves but also because of the interconnected nature of the musculoskeletal system. The recovery journey is multifaceted, involving careful management of the injury, supportive therapies, and a well-planned rehabilitation program.
In managing tendon injuries, incorporating supportive therapies can be beneficial. One such therapy is the use of Carnogel, a carnosine-based gel developed by Chemipower. Carnogel is designed to support muscle, tendon, and ligament health, providing the natural building blocks needed for maintaining healthy, functioning limbs.
Carnosine, known for its anti-inflammatory effects, can aid in muscle recovery and decrease downtime. Its application in Carnogel offers a supportive treatment option that complements traditional veterinary care.
If you are navigating the complexities of tendon injury in your horse, consider incorporating Carnogel into your care strategy.
References:
2. Dyson S. J.2004. Medical management of superficial digital flexor tendonitis
3. Marr C. M., Love S., Boyd J. S., McKellar Q.1993. Factors affecting the clinical outcome of injuries to the superficial digital flexor tendon
4. Lam K. H., Parkin T. D., Riggs C. M., Morgan K. L.2007. Descriptive analysis of retirement of Thoroughbred racehorses due to tendon injuries at the Hong Kong Jockey Club
