The Tendons of the Horse: Healthy Tendons, Tendon Injuries and the Preservation of Tendons
The tendons of the horse are an essential part of its locomotor system. Unfortunately, tendon injuries are common in (sport) horses and rank among the most frequent injuries. A tendon injury is something every horse owner hopes to avoid. Therefore, in this blog, we discuss: the healthy tendons of the horse, tendon injuries and treatments, management and preservation of healthy tendons, and the use of supplements.
The Tendons of the Horse
Tendons are made of fibrous connective tissue and form a connection between muscle and bone. The tendon is composed of longitudinal fibre bundles that are primarily made up of collagen 1. In addition, the tendon also consists largely of water (approximately 55% of the tendon's total weight), which helps reduce friction so that the fibres in the tendon can move easily under pressure during exertion 2. Water is therefore important for the suppleness of the tendon. There are two types of tendons: flexor tendons and extensor tendons.
When muscles contract, the tension on the tendon, which is connected to the muscle, increases, resulting in movement. Due to the force exerted on the tendons, they stretch and then return to their original position. When tendons are overloaded, their structure may change due to the amount of force being applied 3. These changes are irreversible, causing permanent damage to the tendon and ultimately resulting in a tendon injury 3.
Common Tendon Injuries
Tendon injuries most frequently occur in the legs of the horse. Tendons that are regularly injured include the suspensory ligament, the superficial digital flexor, the deep digital flexor, and the check ligament. The suspensory ligament is located against the back of the cannon bone and splits into two branches, which ultimately attach to the sesamoid bones. The superficial digital flexor lies just under the skin and runs, on the back of the leg, from the hock joint along the cannon bone to the pastern. The deep digital flexor also runs along the back of the cannon bone. It lies in front of the superficial flexor, eventually crossing it and attaching to the underside of the coffin bone. The check ligament is located behind the front knee and merges with the deep flexor halfway down the cannon bone.
The Tendons of the Horse
Tendons are made of fibrous connective tissue and form a connection between muscle and bone. The tendon is composed of longitudinal fibre bundles that are primarily made up of collagen 1. In addition, the tendon also consists largely of water (approximately 55% of the tendon's total weight), which helps reduce friction so that the fibres in the tendon can move easily under pressure during exertion 2. Water is therefore important for the suppleness of the tendon. There are two types of tendons: flexor tendons and extensor tendons.
When muscles contract, the tension on the tendon, which is connected to the muscle, increases, resulting in movement. Due to the force exerted on the tendons, they stretch and then return to their original position. When tendons are overloaded, their structure may change due to the amount of force being applied 3. These changes are irreversible, causing permanent damage to the tendon and ultimately resulting in a tendon injury 3.
Common Tendon Injuries
Tendon injuries most frequently occur in the legs of the horse. Tendons that are regularly injured include the suspensory ligament, the superficial digital flexor, the deep digital flexor, and the check ligament. The suspensory ligament is located against the back of the cannon bone and splits into two branches, which ultimately attach to the sesamoid bones. The superficial digital flexor lies just under the skin and runs, on the back of the leg, from the hock joint along the cannon bone to the pastern. The deep digital flexor also runs along the back of the cannon bone. It lies in front of the superficial flexor, eventually crossing it and attaching to the underside of the coffin bone. The check ligament is located behind the front knee and merges with the deep flexor halfway down the cannon bone.
Figuuri 1: Kaavio jänteiden sijainnin havainnollistamiseksi.
A tendon injury can occur in any of the tendons mentioned above. However, injuries to the superficial digital flexor are the most common in the horse 4. Additionally, studies show that in horses with a tendon injury, the injury most frequently occurs in the front legs 5. Certain disciplines within equestrian sports also show a higher incidence of specific injuries. A tendon injury may arise due to acute overload, for example, during training or when the horse injures itself in the pasture. In such cases, the fibre bundles of the tendon are stretched beyond their elastic limit 3. But most often, a tendon injury is caused by chronic overload. Chronic overload involves repeated stress on the tendon, leading to micro-damage that eventually results in a tendon injury 2. This may occur, for instance, when the training intensity exceeds what the horse’s body can currently handle.
How to Recognise a Tendon Injury
To maximise the chance of healing a tendon injury, timely recognition and veterinary involvement are crucial. Symptoms vary depending on the injury and its severity, but a common indication is the appearance of swelling on the leg that feels warm. The warm swelling is the result of the inflammatory response that occurs due to the injury 6. Sometimes horses with a tendon injury are lame. Therefore, pay attention to changes in the horse’s gait, for example, during riding or lunging. However, depending on the injury, lameness may dissipate quickly, leading to underestimation of the injury’s severity and the horse being worked again too soon. It is important to regularly check the tendons for changes such as swelling, so that prompt action can be taken following the onset of a tendon injury.
Treatment of a Tendon Injury
If a tendon injury is suspected, the diagnosis is made via ultrasound performed by a veterinarian. The ultrasound can determine the severity and location of the injury, and shows which phase the injury is in. The acute phase is the first stage of a tendon injury. This is when inflammation occurs, resulting in swelling on the leg that feels warm 7. During the acute phase of the tendon injury, anti-inflammatory medications may be used, and it is especially recommended to cool the leg with cold water for 20 minutes at a time to reduce inflammation 8. Box rest is also sometimes recommended in this phase.
After the acute phase comes the stage where the body forms fibres to heal the injury. However, the tendon fibres that form are made of a different sort of tissue, reducing the elasticity of the tendon, making it different from “normal” tendon fibres 6. To guide the recovery process properly, treatments such as shockwave therapy, stem cell therapy, and platelet-rich plasma (PRP) can be used 8. PRP is a relatively new treatment method in which the horse’s own blood plasma is used for treating and healing tendon injuries. With stem cell therapy, stem cells from the horse’s bone marrow are used for recovery. Shockwave therapy is applied by delivering pressure waves to the tendon. In addition, laser therapy is regularly used in tendon injury treatment.
Based on the severity of the injury, its location, and its phase, a treatment plan will be made. A rehabilitation schedule is also created, including controlled movement and exercise. Movement stimulates blood flow and circulation in the tendon, which has a positive effect on tendon healing. This schedule differs depending on the injury and its severity. Rehabilitation can last from 3 months up to more than a year 8. However, the tendon is a body part with poor blood supply. This limits the removal of waste products and delivery of nutrients, making tendon healing slow. Proper rehabilitation is important both for healing and for preventing repeat injury. The goal of rehabilitation is to bring the quality of the tendon tissue as close as possible to its original state, although full restoration to the original quality is unfortunately not achievable.
Management Tips for Preventing Tendon Injuries
Tendon injuries are better prevented than cured. Therefore, a few things should be taken into consideration to maintain healthy tendons.
Gradually build up your horse’s training and ensure that the body can properly recover from training changes 6. This allows the body, especially the tendons, time to adjust to changing physical demands. Moreover, good overall fitness and the development of strong muscle mass are important for preventing tendon injuries. Proper nutrition and daily free movement are essential for optimal physical condition.
While it is sometimes discouraged to ride on different surfaces, it can be beneficial to occasionally train your horse on different types of surfaces. It is important, however, that the surface is not too slippery or has many holes where the horse can misstep and fall 6.
Ensure that your horse is shod and/or trimmed correctly and on time. If this is not done, the position of the hooves changes, which can affect the load on the tendons of the horse 6.
Cool the tendons after intense exertion by hosing them with cold water or using cooling products such as clay, a cooling gel, or specialised cooling bandages.
Also, check your horse’s tendons regularly for changes to detect issues as early as possible.
Supplements for the Tendons of the Horse
Supplements can be used to support tendons and joints. Widely used ingredients include collagen and MSM.
Collagen is a naturally occurring protein found in the horse’s tendons. Studies show that collagen is an important component of the tendon and plays a role in tendon healing after injury 9. Synovium Agility contains bioactive collagen peptides for supporting tendons and joints.
Methylsulfonylmethane (MSM) is an organically bound sulfur compound that is essential for amino acid and protein synthesis and tissue production. Moreover, MSM functions as an antioxidant and neutralises free radicals released during heavy exertion 10. Synovium MSM Pure, Synovium MSM Optimal-C and Synovium Motion JMT all contain MSM to support the tendons of the horse.
Omega-3 fatty acids are also often used because of their anti-inflammatory properties. Research shows that these fatty acids have a positive effect on inflammation markers in the body 11. Linseed oil and algae oil are examples of oils with a favourable omega-3 ratio.
In short, it is of great importance to prevent tendon injuries through proper management, training, and nutrition. Regularly check the tendons for changes and always consult a veterinarian in case of doubt so that a suitable treatment and rehabilitation plan can be established if a tendon injury occurs.
References
1. O’Brien, C., Marr, N., Thorpe, C. (2021) Microdamage in the equine superficial digital flexor tendon. Equine Veterinary Journal, 53(3):417-430.
2. Shojaee, A. (2023) Equine tendon mechanical behaviour: Prospects for repair and regeneration applications. Veterinary Medicine and Science, 9(5):2053-2069.
3. Dahlgren, L.A. (2007) Pathobiology of Tendon and Ligament Injuries. Clinical Techniques in Equine Practice, 6:168-173.
4. Thorpe, C.T., Clegg, P.D., Birch, H.L. (2010) A review of tendon injury: Why is the equine superficial digital flexor tendon most at risk? Equine Veterinary Journal, 42(2):174-180.
5. Lam, K.H., Parkin, T.D.H., Riggs, C.M., Morgan, K.L. (2007) Descriptive analysis of retirement of Thoroughbred racehorses due to tendon injuries at the Hong Kong Jockey Club (1992–2004). Equine Veterinary Journal, 39(2):143-148.
6. Williams, J., Chatham, A. (2012) Equine tendons: reducing the risk of injury. The Veterinary Nurse, 3(1):20-28.
7. Barrett, J., White, N.A. (2008) Introduction to Equine Tendon Injury. AAEP Proceedings, 54:464-469.
8. Smith, R.K.W. (2024) Treatment of tendinopathies. Equine Veterinary Education, 36:659-627.
9. Dahlgren, L.A., Brower-Toland, B.D., Nixon, A.J. (2005) Cloning and expression of type III collagen in normal and injured tendons of horses. American Journal of Veterinary Research, 66(2):266-270.
10. Marãn, G., Mũoz-Escassi, B., Manley, W., García, C., Cayado, P., de la Muela, M.S., Olábarri, B., León, R., Vara, E. (2008) The effect of methyl sulphonyl methane supplementation on biomarkers of oxidative stress in sport horses following jumping exercise. Acta Veterinaria Scandinavica, 50(1): 1-9.
11. Manhart, D.R., Scott, B.D., Gibbs, P.G., Coverdale, J.A., Eller, E.M., Honnas, C.M., Hood, D.M. (2009) Markers of Inflammation in Arthritic Horses Fed Omega-3 Fatty Acids. The Proffesional Animal Scientists, 25(2):155-160.