Common Leg Faults of Horses II: Forelimb

Normal horses bear between 60% and 65% of their weight on the forelegs. This may vary due to conformation, e.g. heavy-headed, long-necked horses will put more weight on their front legs than small-headed, short-necked horses. Proper angulation of the limbs as well as proper length of long bones are necessary to stop future problems arising. The horse may have good conformation from the front view, but be badly conformed when viewed from the side.

Anterior deviation of the carpal joint (Bucked Knees)

These horses are presented with forward displacement of the knee when viewed from the side. It may be related to contraction of the flexor muscles of the forearms attached to the knee and/or the flexor tendons. The former is a simple deficit and rarely worries the foal or adult horse. However where both knee (deviated forwards) and the fetlock (deviated down and backwards) deviates occur together, the horse is generally unsound and cannot usually stand up to hard usage.

Posterior deviation of the carpal joint (Calf Knees)

When viewed from the side, with the horse standing straight, this is seen as a backward displacement of the knee. This is a particularly bad fault because it predisposes to lameness both from injuries to the carpal bones (knee bones – often leading to knee chips) and from the great strain which is placed on all ligaments and tendons down the back of the leg.

Where displacement is severe, sprain of the flexor tendons also becomes a limiting factor. While corrective shoeing with raised heels can be helpful, care must be taken not to over flex the pastern joint which can destabilize the leg further, leading to joint as well as tendon problems.

Sideways displacement of the cannon bone (Bench Knees)

When viewing the horse from the front, the cannon bone is not centered squarely under the knee. Displacement is lateral, that is, towards the outside. Lateral displacement causes excessive stress on the medial (inside) portion of the cannon bone and this usually results in the formation of splints. This is a bad defect, which appears to be heritable.

Open Knees

This is best viewed from the side of the horse. The knee looks corrugated instead of smooth, and mostly this is an age factor with the gaps in the knee closing with maturity over 3 years. However, some horses may never lose this appearance and, in these cases, this weakness leads to injury of the carpal bones.

Lateral radiographs taken of these knees usually show actual deformities of the lower (distal) end of the radius with the actual joint-bearing surface being slightly deviated backward, thus giving a backwards placement of the actual knee (carpal) bones themselves. These are permanent defects.

Splints

A splint is usually associated with injury to the ligament between the second and third, or third and fourth, metacarpal or metatarsal bones, that is, between the cannon bone and either the inside or outside splint bones respectively. When tearing of this ligament occurs due to injury, faulty conformation or faulty nutrition, an inflammation of the outside lining of the splint bone and/or cannon bone occurs. Growth of the splint depends on the amount of original damage and whether the cause has been removed or is continuing to irritate the affected area.

Splints are more commonly found on the inside of the front and the outside of the hind cannons because of the anatomical make-up of the knee and hock respectively. Consequently, any change in conformation that places more weight on the medial aspect (inside) of the knee joint or the lateral aspect (outside) of the hock joint will have a tendency to produce splints.

Other factors influencing the occurrence of splints include inherited smallness of the cannon bone, lateral displacement of the cannon bone (bench knees) and occasionally it is seen in bow-legged horses with closer than normal feet. Splints also occur by injury through carrying too much weight at too young an age, and by any other cause of excessive strain on the splint ligaments. The one coming most readily to mind being excessive body weight due to overfeeding and mineral imbalances in show hacks.

Splints may appear when calcium: phosphorus ratios in the feed are not correctly balanced. Treatment relies on removal of the cause followed by surgical shoeing and/or a long rest period. Occasionally, surgery on the splint itself may be necessary. Obviously, where the condition is due to faulty conformation such as bench knees, there is a much slighter possibility that either rest or surgery will effect a permanent cure. All horses treated surgically should be given complete rest for 6 months following surgery and, if applicable, should have their body weight reduced.

Pastern problems

Horses that have pasterns deviating from normal conformation usually have difficulties if asked to perform heavily either as endurance, racing, jumping or eventing horses.

The pastern may be short and upright, even to the point of being almost perpendicular. This leads to severe concussion of the joint surfaces of the fetlock, pastern and pedal joints and often leads to increased joint fluid effusion which shows as distension of the joint capsules and also lameness. This is not an uncommon lameness in heavy young horses given too much exercise when immature.

Early lameness may not give any evidence on radiographs and is more a clinical disease needing selective nerve blocks to diagnose.

Where the pastern is long and sloping the joint surface can again be damaged, particularly the front of the fetlock joint and the front of the lower end of the cannon bone. Also, there is usually damage to the flexor tendons and sesamoidean ligaments, often with lameness causing increased tendon sheath enlargement. Use of ultrasound may be more diagnostic than radiographs. Both forms can lead to increased incidence of Wind Galls.

Wind Galls

These are found as soft swellings slightly above and behind the fetlock joint. They commonly occur in the front legs, but may occur on the hind legs, especially in jumping horses. Such swellings are directly due to an over-secretion of joint fluid caused by some ‘irritation’ to the joint surfaces or joint capsule of the fetlock joint. Occasionally, they are also due to excess tendon fluid in the tendon sheaths behind the fetlock joint. This ‘irritation’ can be due to one or several causes – overwork in young heavy horses, poor conformation, development of OCD (Osteochondrosis dissecans), tearing of ligaments, tendons and joint capsules, and injuries to articular cartilage in the joint.

The result in both cases is inflammation with excess production of joint fluid. This may occur without lameness but usually the swelling tends to increase in size with work. Reduction in the amount of work or spelling gives a reduction in size, even to the point of a complete recovery, until the horse is worked again.

It should be realised that wind galls themselves are not a disease, but are only a symptom of trouble occurring within the joint or tendon sheath. Consequently treatment must be directed at the cause of the problem, not just at treatment of the accumulation of fluid within the joint capsule.

By Dr Reginald R. R. Pascoe AM - Last updated 16 November 2012