A conformation or plumbness defect can trigger certain lameness or be the cause of chronic problems such as osteoarthritis. A minimum of knowledge of the horse’s general conformation and plumbness is therefore required. A rule of thumb is to recognize the differences in conformation from one breed to another. Here we will only discuss a few points that concern defects in conformation and plumbness of the limbs. Generally, to evaluate a horse it is necessary to observe it from a distance as well as up close, at rest and at the trot. The owner or the veterinarian who must assess the conformation of a limb must also consider the age, to know if he is in presence or not of a defect related to a disease of the locomotor development of the foal.
Defects of plumbness in the horse
When a horse is too tight or too open in the front, we are looking at an example of a conformation defect in the forelegs. When looking at the horse from the front, one can see that the distance between the points of the shoulders is respectively greater or less than the distance between the vertical axes of the feet. These anomalies are often combined with a splayfooted (the claws of the hooves are turned outwards) or a pigeon-toed conformation (the claws of the hooves are turned inwards). Still observing the horse from the front, one can observe that the carpals are turned inwards and too close to each other; this is known as ox-knees and predisposes to carpal tunnel syndrome and carpal joint injuries. If the deviation of this joint is towards the outside, increasing the distance between the two carps, we speak of cambered knees, which can also lead to degenerative lesions and joint problems in the long term.
When observing the forelegs in profile, one can find a deviation of the carpal joint towards the back or towards the front; these two types of conformation are referred to as hollow knees and crooked knees. In the former case, the horse is prone to carpal tunnel desmitis due to excessive tension and to chip fractures of the dorsal surface of the carpal bones, while the latter may result in abnormal pressure on the sesamoids or a predisposition to deep flexor tendonitis.
The conformational defects of the hind limbs can be seen from behind and in profile. As with the forelegs, the horse may be too tight or too open from behind. In the former case, and if the animal has normal conformation in the forelegs, interference may occur between the forelegs and hindlegs. Horses with hocks turned inwards (ox hock) or outwards may be observed. This conformation is very bad because it imposes an excessive load on the internal part of the small tarsal joints, which predisposes to degenerative phenomena of these joints (spavin). Seen from the side, the horse may be under it from the rear from the root of the limb or present an exaggerated angle at the hock joint. In the latter case, the horse becomes hind quartered from the hocks, often resulting in inflammation of the ligaments in the plantar region of the hock. A horse is said to be hind quartered when the whole of its hind leg is shifted backwards, this conformation will often go hand in hand with a too vertical orientation of the pasterns.
Finally, it is not possible to ignore the conformation of the foot when talking about a horse. Indeed, the saying goes: “no foot, no horse”, and a good conformation of the foot is essential to prevent many of the conditions that result in lameness and disability of the animal. A balanced and symmetrical foot means that each time the foot touches the ground, it distributes forces evenly and reflects them to the center of the bony column of the limb above.
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Orthopedic developmental diseases in the horse
Angular deviations such as contracture or flaccidity of the limbs are grouped under the same term: developmental orthopedic diseases or diseases of locomotor development.
Angular deviations
Angular deviations of the horse’s limbs include valgus (if the angle is open to the outside), varus (if the angle is open to the inside), rotation or a combination of deviations. Some factors that contribute to an angular deviation are immaturity of the periarticular tissue that causes joint instability, uneven growth of the distal growth plate of the radius, tibia or main metacarpal/metatarsus, ossification defect or necrosis of the cuboid carpus or tarsus bones.
For each case, the veterinarian decides whether to apply conservative treatment (limited exercise, diet correction), orthopedic treatment (external prosthesis, foot trimming, corrective shoeing) or surgical treatment. Surgical treatment is performed under general anesthesia. It consists of two techniques: either stimulation of bone growth (on the side where it is less) or the use of screws and cerclage to delay it – on the side where growth is greater. But all these techniques are effective only if the owner recognizes the problem in his breeding, so that he can consult his veterinarian as soon as possible. For a deviation of the distal part of the main metacarpus/metatarsus, action should be taken before eight weeks of age, and for a deviation involving the distal part of the tibia or radius, action should be taken before twelve weeks.
Rotations are deviations in the horizontal plane of the limbs that can be observed when standing in the axis of the horse. In adults, many primary rotations are encountered. The toe of the foot is either directed outwards (splayfooted) or inwards (pigeon-toed). In foals, this rotation is often secondary to an angular deviation, and, in many cases, a spontaneous correction occurs with growth or after correction of the deviations.
Contracture
There are congenital or acquired flexor contractures. They concern the carpal joints, the metacarpophalangeal joints (fetlock) and the proximal (pastern) or distal (foot) interphalangeal joints. In congenital contractures in newborn foals, there is often spontaneous resolution within hours of birth, but if the contracture is moderate, medication and bandaging, including prosthesis, may be used. In severe cases, surgery should be considered.
Acquired contractures, also called growth contractures, involve either the superficial or the deep flexor tendon. In the first case, foals between eight and eighteen months of age are mostly affected. They show an image of a fetlock deviated forward. Treatment varies according to the extent of the problem and consists of reducing energy intake, bandaging, corrective trimming, orthopedic shoeing and sectioning the radial flange. If the deep flexor tendon is affected, the foal, usually three months to one year old, will develop a clubfoot or creep, i.e., distal interphalangeal flexion with increased heel size. The basic principle of treatment will be the same as for the superficial tendon except that a section of the carpal tunnel may be used.
Flaccidity of the flexors or “digital hyperextension
The hind limbs are more often affected than the front ones. There is a congenital form in premature foals or foals with systemic diseases and an acquired form such as when they are immobilized for a long time in a cast. Typical signs in affected animals are digital hyperextension and fetlock descent. In many cases, the problem will resolve spontaneously within two to three days. However, to help the foal, it should be placed on a shallow, firm bedding and given limited exercise. The goal is to promote muscle development. Bandages or prostheses should never be used and if the problem persists, the foal should be helped with corrective trimming and an orthopedic shoe.
For more information: the horse’s legs
