Leg thick, horse lame, is it the tendon?

The tendons are part of the musculoskeletal system and act as the connecting links between the muscles and the skeleton. They consist of strong, flexible tissue, transfer energy from the muscles to the bones, and thus enable targeted movement. Their special structure, consisting of parallel connective tissue fibers grouped together in bundles, gives them enormous tensile strength and elasticity. The flexor tendons of the front legs are particularly exposed to extreme stress in horses, as more than half of the body weight has to be carried by the forehand. Tendon damage is one of the most common causes of lameness, especially in sport horses. In most cases, the structures affected on the front leg are the superficial flexor tendon, the deep flexor tendon, the suspensory ligament, and the fetlock joint (see diagram). As there are very few nerves and blood vessels in the tendon tissue, healing is very slow.

INHALT
Structure Causes Origin and classification Symptoms Diagnosis Therapy Forecast
Structure

Below the tarsometatarsal joint, the suspensory ligament, the superficial and deep flexor tendons run along the back of the cannon bone. When the leg is raised, the three structures can be felt as soft, movable strands under the skin.

The suspensory ligament is a tendon-like strand with a certain proportion of muscle fibers, which originates at the back of the tarsal joint and the upper end of the cannon bone and then runs down between the pastern bones at the rear. Above the two suspensory ligaments, it divides into two parts, each of which runs across the suspensory ligaments to connect to the extensor tendon at the front. The fetlock joint serves to stabilize the fetlock joint when the horse is standing and, together with the suspensory ligaments and suspensory ligament ligaments, forms the fetlock joint apparatus.

The deep flexor tendon with its supporting ligament lies between the fetlock joint and the superficial flexor tendon and runs from the back of the tarsometatarsal joint over the back of the cannon bone to the coffin bone. The superficial flexor tendon envelops the deep flexor tendon and runs over the pastern bones to attach to the coronet bone.

Diagram of the distal tendons of the horse
1 Tendon sheath | 2 Tendon sheath support ligament | 3 Superficial flexor tendon | 4 Deep flexor tendon | 5 Deep flexor tendon support ligament | 6 Suspensory ligament | 7 Lower common ligament
Causes

The development of tendon damage is always determined by various factors. The strain placed on the tendons through the use of the horse in different equestrian disciplines plays a major role. Wear and tear and excessive strain can lead to damage to the tendon tissue, especially if work is started too quickly and too intensively and warm-up phases are neglected. Deep, uneven ground and muscle fatigue can also lead to tendon damage due to the resulting lack of coordination. Other contributing factors include limb malalignment, unfavorable hoof shapes, obesity, and errors in feeding or rearing. With the petsXL health passport, you can clearly store and monitor your horse's weight data.

Origin and classification

It is believed that the actual tendon inflammation is preceded by pre-existing damage to the tendon in the form of reduced blood flow, which is caused by the blood vessels also being stretched significantly during exercise. Tendon inflammation, also known as tendinitis, is caused by the tearing of small or large fibers or entire fiber bundles of the tendon. As this also causes blood and lymph vessels to tear, bleeding occurs in the healthy areas, damaging further tendon fibers. As the condition progresses, fluid accumulates and the affected area thickens, which is also visible externally. The interrupted blood supply and the release of enzymes can cause further damage to the tissue. An inelastic replacement tissue forms in the area of the lesion, which has far worse properties than the actual tendon tissue.

A distinction is made between aseptic (non-infected), acute, and chronic inflammation. Furthermore, defects of individual fibers, fiber bundles, and partial and total defects are distinguished.

Symptoms

In cases of acute tendon inflammation, moderate to severe lameness occurs depending on the severity of the damage. The affected area is warm to the touch, clearly painful, and initially swollen in a diffuse manner. Increased pulsation of the metatarsal artery can be felt at the fetlock joint. In cases of extensive or total tears, there is severe lameness in the fetlock joint and the affected limb is often relieved of weight.

Chronic inflammation of the superficial flexor tendon is usually accompanied by only slight or no lameness. Pain and warmth are usually no longer detectable. The formation of replacement tissue leads to a change in the shape of the tendon. In profile, it no longer appears straight, but curved. This phenomenon is therefore also referred to as a bow, calf, or banana. Due to the limited elasticity of the scar tissue, fiber tears can occur again, which can turn chronic inflammation into acute inflammation.

Defects in the deep flexor tendon show similar symptoms, but due to their deeper location, swelling is usually not visible from the outside. Chronic inflammation of the deep flexor tendon can lead to deformation of the hoof. The scar tissue that forms in the defect leads to reduced elasticity of the deep flexor tendon, which causes increased tension on the tendon attachment to the hoof bone. The hoof becomes blunter and a so-called club hoof develops.

Diseases of the suspensory ligament can cause a wide variety of symptoms. Some horses show lameness with classic signs of inflammation such as swelling, warmth, and pain, while others show only slight lameness without any swelling of the affected leg. Accurate diagnosis is therefore particularly important in this area.

Diagnosis

If the above symptoms are present, a veterinary examination must always be carried out immediately to prevent further damage to the tissue through additional strain. However, the veterinarian cannot make a definitive diagnosis based on the lameness examination and the symptoms alone. Only with the help of an ultrasound examination can a tendon defect be diagnosed and precisely localized.

If no swelling is visible despite lameness, the veterinarian can better pinpoint the location of the damage with the help of conduction anesthesia (local injection around the nerves). In cases of suspensory ligament damage, X-rays should always be taken, as suspensory ligament inflammation can also be caused by phalangeal fractures, among other things, and changes at the origin of the suspensory ligament can often be seen on an X-ray.

Ultrasound tendon horse
Tendon damage, such as here in the superficial flexor tendon, can be visualized using ultrasound
Therapy

The most important measure in the treatment of tendon disorders is immobilization. Due to the slow healing process, the length of the rest period varies depending on the size of the defect.

Anti-inflammatory medication and cooling bandages are used in the acute inflammatory phase. Once this phase is over, warming bandages are applied to improve blood circulation and resorption. Another promising treatment method involves the local injection of certain medications directly into the damaged tendon.

Regular ultrasound examinations can be used to monitor the healing process and, depending on the ultrasound findings, the veterinarian will decide when controlled movement can be resumed. Adherence to an exercise plan tailored precisely to the horse in question and the extent of the damage is at least as important as the actual therapy, as this is the only way to ensure that the regenerated tendon regains maximum resilience.

Forecast

Due to the scar tissue that forms, which cannot be compared to the actual tendon tissue in terms of quality, the original load-bearing capacity cannot always be fully restored. Many affected horses can be returned to sport with the help of a carefully tailored therapy and appropriate exercise program, provided that all accompanying factors, such as deep ground, hoof shape, or misalignments, are identified and addressed. The prognosis varies depending on the extent and severity of the damage, the age of the horse, and its intended use.

In general, tendon injuries have a long healing process of approximately 4 to 12 months.