Ringbone is an unfortunate affliction that affects some horses as they age. The term ringbone is used to describe osteoarthritis in either the pastern joint (high ringbone) or the coffin joint (low ringbone). When horses are diagnosed with ringbone, it is important to make a distinction between high and low ringbone, as the specific type may affect treatment and the horse’s prognosis.
Two more important terms to understand when discussing ringbone are articular ringbone and periarticular (also call non-articular) ringbone. Articular ringbone often affects the entire joint—causing problems with the cartilage and the joint lining (synovium) that make the joint enlarged, painful and stiff. When a horse has articular ringbone, x-rays show partial or complete narrowing of the joint space, new bone growing into the joint (called osteophytes), increased density of the bone directly beneath cartilage (called sclerosis), or erosion of the bone beneath cartilage (called lysis).
Periarticular ringbone affects the soft tissues, including the ligaments and tendons, around the joint. Radiographs of horses with periarticular ringbone show bone growth away from the joint. It may occur where the ligaments attach to the bone or joint capsule (called enthesophytes) or anywhere that the connective tissue that covers the bone has been damaged.
What Are the Causes?
Not all older horses get ringbone—and, while not common, ringbone can affect a younger horse. While there is no sure way to determine which horses will develop ringbone, there are several factors that contribute:
• Poor conformation. Overly upright pasterns, angular limb deformities, toeing in, and toeing out all lead to increased concussion put on the joints, which can cause ringbone.
• Trauma. Strains and sprains to the soft tissues surrounding the joint also lead to ringbone. This type of trauma is most common with performance horses who routinely make sudden stops and sharp turns, such as polo ponies and reining and cutting horses. Joint infections may also result in ringbone.
• Developmental factors. Osteochondrosis dessicans (OCD) and subchondral cyst-like lesions (bone cysts) also predispose a horse to develop ringbone later in life.
• Long-term concussion and hard work. Performance horses who endure concussion and hard work have a greater tendency to develop ringbone. This includes western performance horses, barrel racers, eventers, race horses and jumpers. cont.
• Nutritional imbalances. Horses who suffer poor nutrition, especially early in life, may be more likely to develop ringbone as they age.
• Poor hoof care. A lifetime of improper trimming and shoeing can put unusual pressure on the joints of the horse’s leg, which can lead to ringbone.
Ringbone may initially go undiagnosed. The first sign a horse shows is lameness, and many equine professionals will first lay the horse up to see if it goes away. In the case of ringbone, the rest will make the horse appear sound, but he usually becomes lame again after he goes back to work. So how can you differentiate general lameness and ringbone? Initially, lameness may be accompanied by two signs that the horse is suffering from ringbone: a warm swelling around the pastern area that goes away with rest, and sensitivity to any pressure put over the pastern joint. As the disease progresses, the warm swelling turns to a firm, cool enlargement of the pastern area, and the horse often becomes progressively more lame.