Fetlock is a term used for the joint where the cannon bone, the proximal sesamoid bones, and the distal phalanx (pedal bone) meet. In some ways it is comparable to the ankle joint in humans. The pastern is the area between the hoof and the fetlock joint. Disorders of the fetlock and pastern include conditions such as fractures, osselets, ringbone, sesamoiditis, synovitis, and windgalls.

Fractures of Phalanges and Proximal Sesamoids

Fractures of the long pastern bone (first phalanx) are not uncommon in racehorses. They may be small “chip” fractures, fractures along the length of the bone (split pastern), or fractures in which the bone is broken into fragments. Another category, seen only in Standardbreds, involves chips or loose fragments on the back of the long pastern bone called Birkeland fractures.

Signs of longitudinal fractures involve sudden, severe weightbearing lameness after work or a race. There may be little or no swelling initially, but there is intense pain on feeling or bending the fetlock joint. Lameness may be less obvious with chip or fragmented fractures, but bending the joint worsens the problem. X-rays confirm the diagnosis, although it can be difficult to see the fine line of the fracture.

Chip and fragmented fractures can be surgically removed using an endoscope. Long, split fractures can be repaired using 2 or more bone screws. Conservative treatment of severely fragmented fractures involves using a plaster or fiberglass cast for up to 12 weeks. However, complications include poor alignment at the fracture site and secondary arthritis.

Fractures of the short pastern bone (second phalanx) are similar to those of the long pastern bone, but they are less common. The treatment and outlook for recovery are similar.

Fractures of the fetlock (proximal sesamoid) bones are relatively common. They are caused by overextension and often are associated with damage to the ligament, as in the forelimb of Thorough-breds. Shoeing with a trailer-type shoe may cause fractures of the fetlock in the hindlimb of Standardbreds. Signs of fracture include heat, pain, and sudden onset of lameness; these tend to worsen when the fetlock joint is bent. There is bleeding and fluid buildup in the fetlock joint. X‑rays confirm the diagnosis.

The outlook for recovery is fairly good if small fragments are surgically removed as soon as possible. Standardbreds respond more favorably than Thoroughbreds. The outlook for recovery in large fractures at the base of the fetlock bone is poor, regardless of the treatment. Very severe damage to the suspensory ligaments, including fracture of both sesamoid bones, is a catastrophic injury and can cause a compromise of blood flow to the foot. Some horses can still be used for breeding by surgical immobilization of the fetlock joint so that the bones grow solidly together.

Osselets

Osselets refers to inflammation of the connective tissue that surrounds the cannon bone (between the fetlock joint and the carpus) and the fetlock joint. The inflammation may involve arthritis and can progress to degenerative joint disease. The condition is an occupational hazard for young Thoroughbreds and is caused by the strain and repeated trauma of hard training in young horses.

The gait of a horse with osselets becomes short and choppy. Applying firm pressure and bending the fetlock joint will cause pain. Swelling, which may be warm and sensitive, is seen over the front and sometimes the side of the joint. In the initial stages, x-rays may show no evidence of new bone formation, in which case the condition is called “green osselets.” Later, a disorder may be seen in the attachments of bones to the fetlock joint. Bone spurs or newly formed bone in the affected area may break off and float loosely in the joint. Such loose fragments are called joint mice.

Early cases may be cured by rest, which is very important to treatment. The application of cold packs over several days may relieve inflammation. Anti-inflammatory drugs given by mouth or injection may also be used. Corticosteroids may be injected into the joint as well. However, this and other forms of anti-inflammatory medication, if used along with continued training or racing, will inevitably lead to the destruction of the joint surfaces.

Ringbone

Ringbone is inflammation of the connective tissue surrounding the pastern bone or osteoarthritis in the digits. It leads to the development of spurs or outgrowths of bone. Causes include poor conformation, improper shoeing, or repeated jarring injury from working on hard ground. Trauma and infection, especially wire-cut wounds, are other causes. In light horses, the condition may result from strains on ligaments and tendons in the pastern region.

The pastern may become bell-shaped when affected by ringbone. Inflammation of the connective tissue will initially cause lameness. The lameness may subside once the bony outgrowths appear, particularly if the surfaces of the joint are unaffected. If joint surfaces are involved, lameness tends to persist, sometimes leading to the fusion of the bones to the joint. Your veterinarian will diagnose the condition by physical examination of your horse, use of regional analgesia to identify the location of pain, and x-rays to confirm the findings.

Complete rest is the most important requirement for treatment. Cold and astringent applications as well as radiation therapy in the early stages may be beneficial. Anti-inflammatory medication may relieve the signs of lameness. Surgically immobilizing the pastern joint so that the bones grow solidly together will cure the condition.

Sesamoiditis

The sesamoid bones in the fetlock are kept in position by ligaments. Due to the great stress placed on the fetlock during racing, the attachment of some of these ligaments can tear, resulting in sesamoiditis.

The signs of sesamoiditis are similar to—but less severe than—those resulting from sesamoid fracture (see Bone, Joint, and Muscle Disorders in Horses: Fractures of Phalanges and Proximal Sesamoids). The amount of lameness or swelling will depend on the extent of the damage. Reduced speed may be the only sign of lameness. A veterinarian will look for pain and heat while bending the fetlock joint, but x-rays are necessary for accurate diagnosis and evaluation.

The recommended treatment is a 2- to 3-week course of an anti-inflammatory drug. Mild cases of sesamoiditis require 6 or more months of rest; severe cases require 9 to 12 months. Despite various treatments, the outlook for recovery is guarded or poor. Even after 9 to 12 months of rest, many horses become lame within weeks after resuming training.

Villonodular Synovitis

The cause of this inflammation of the membrane surrounding the forelimb fetlock joints is unknown. Affected horses may be 2 to 18 years old, with a slightly higher incidence in males. Signs include nodules that form around the fetlock joint. Swelling and lameness may or may not be present. Changes to the surrounding bone and cartilage may occur.

To diagnose villonodular synovitis, your veterinarian will examine your horse for the presence of nodules or small lumps around the joint. X-rays confirm the diagnosis. The nodules are surgically removed; smaller masses can be surgically removed by using an endoscope. Radiation therapy appears to help prevent recurrence after surgery.

Windgalls (Windpuffs)

These puffy, fluid-filled swellings around the fetlock joints may affect the forelimbs, hindlimbs, or both. They generally are not accompanied by heat, pain, or lameness. Trauma and hard exercise are believed to contribute to the condition, but the exact cause is uncertain. Some horses, particularly heavy ones, seem to be more susceptible than others. In the absence of lameness, treatment is not warranted. Windgalls may disappear spontaneously or respond to periods of rest, bandaging, and exercise. Recurrence is common, however.

Last full review/revision July 2011 by Russel R. Hanson, DVM, DACVS, DACVECC; Joerg A. Auer, DrMedVet, Dr h c, MS, DACVS, DECVS; Andrew P. Bathe, MA, VetMB, DACVS, DEO, MRCVS; Leo B. Jeffcott, MA, BVM, PhD, FRCVS, DVSc, VD; Svend E. Kold, DMV, MRCVS, RCVS Specialist in Equine Surgery (Orthopedics); C. Wayne McIlwraith, BVSc, PhD, DSc, FRCVS, DACVS; Dale A. Moore, MS, DVM, MPVM, PhD; Sheldon Padgett, DVM, MS, DACVS; Tracy A. Turner, DVM, MS, DACVS, DABT; Stephanie J. Valberg, DVM, PhD, DACVIM; John F. Van Vleet, DVM, PhD