When examined from behind the normal conformation of the hindlimb should show the pin bone, hock and centre of the foot to be in a perpendicular line. When viewed from the side, a perpendicular line from the pin bone should touch the point of the hock at the back and be parallel to the hind cannon to the ground.
These legs are responsible for the major propulsion of the horse and any changes to a less than good conformation can lead to lameness problems, especially in immature horses.
The horse should be viewed from behind to assess the same perpendicular straightness as seen in the front leg from the front of the horse. Failure to meet this simple test may indicate future problems of weight bearing in the stifle, hock and lower joints.
When viewed from behind the hocks are closer together than normal and usually the lower leg is also displaced laterally (outwards). Many horses show this condition to a slight extent but when the hocks actually touch behind it is considered very undesirable, as this leads to brushing of the hocks and excessive strains on the tendons and ligaments around the joint.
In adult horses, this condition may predispose to articular problems and lead to ‘bone spavin’. The condition occurs because of continuous strain and irritation on the medial side (inside) of the hock joint and gradually leads to the deposit of extra new bone. This encroaches into the joint capsule and joint, causing pain and lameness. In some cases, after a very long protracted course of lameness, ankylosis of the joint involved may occur with diminution of lameness.
Once ankylosis has occurred, the lameness usually becomes markedly reduced, even to the point of the horse becoming useful again. Surgical procedures can be used to accelerate this healing and are mainly successful for low bony spavin; recovery time may be 6 - 12 months.
Excessive angulation of the hock (Sickle Hocks)
Where there is excessive angulation of the cannon and hock when viewed from the side, the horse appears to be standing with the cannon angled forwards under it’s body. This predisposes foals and yearlings to ‘curb’, which is a sprain of the plantar ligament (which holds the hock and hind cannon together at the back of the leg).
These horses are also predisposed to the development of bony spavin in the same manner as cow-hocked horses.
Sprains are painful and result in lameness. Reduced exercise helps but severe cases often remain lame for long periods, frequently going lame when exercised. Old horses occasionally form fibrous tissue in the area, which may strengthen the leg for walking but often show lameness if the horse is worked.
This is a serious defect and as there is some evidence it is heritable, efforts should be made to cull bad cases from breeding stock
The most serious defect is the combination of sickle and cow hocks. This results in excess strain on the whole hock and will eventually cause permanent lameness, most commonly related to bony spavin. Remedial shoeing in cutting horses may be attempted by using small heel cogs on the inside of the hind shoes. Where the horses are used for other purposes, a small trailer on the inside heel, again with a short cog, may help correct this condition. This cannot be used successfully if the horse brushes the hind legs during work.
The hindleg can be too straight, to such an extent that the femur and tibia appear to have very little angulation. The area over the stifle joint appears dimpled and the patella is easily rocked in and out of position. This condition predisposes to locking patellas, which can result in low-grade arthritis of both stifle and hock joints, leading to chronic low-grade lameness.
The hock is correspondingly straight. In excessive over-straightness a wrinkled appearance due to insufficient tension in the flexor tendons may be seen at the back of the hock. This type of conformation in the hock predisposes to sprain of the hock ligaments and joint capsule, and can lead to bog spavin. Bog spavin shows as a soft swelling of the joint capsule on the inside, outside and occasionally, the back of the hock joint.
The enlargement of the tendon sheath of the tendons passing through the hock area is called thoroughpin. While it is usually related to the flexor tendons at the back of the hock, the term is occasionally used to describe the same enlargements if they occur in the extensor tendons down the front and outside of the hock.
This distension of the tendon sheath often appears without warning and may even be present in foals at birth. If lameness is not present, it remains as a blemish; if however it is caused by injury to the tendon or the tendon sheath, it may cause lameness. In this case it must be regarded as unsoundness. The cause in newborn foals is unknown.
The course of the enlargement in older horses is usually slow and is assumed to be related to continuous low-grade injury to the tendon and tendon sheath. Where no pain is evidenced and no lameness produced, then it remains as an unfortunate blemish, as it usually has a poor response to any treatments.
Any performance horse that has poor conformation of the foot can never be free of problems. A well-proportioned foot with a large frog, deep soles and thick walls is ideal, and should be sought for if trouble-free riding is desired.
There is a tendency in some family lines of horses to have small feet. This often leads to feet troubles, such as pedal osteitis (solar laminitis) and concussive problems in the fetlock joint. Overly small feet are usually inherited and it is in the best interest of any breed to endeavour to reduce the incidence of such problems.
Other serious defects in the foot are related to foot deviations, such as pigeon toes. If this occurs in with smaller than normal feet, it often leads to ligament and joint sprains, causing lameness and loss of performance.
Care in the selection of horses to minimize the effects of the above conditions increases the chances of obtaining a horse for many years of useful performance.