Ringbone is one of the most common forms of arthritis diagnosed in the horse and is a “catch-all” term used to describe an osteoarthritis that afflicts the coffin joint (low ringbone) or the pastern joint (high ringbone).
Degeneration of the joint interferes with function, mobility and flexibility of the lower limb and ultimately leads to varying degrees of pain and non-weight-bearing lameness.
The first joint from the ground up in a horse’s limb is the coffin joint. It is located within the hoof capsule and lies between the coffin bone (P3) and the short pastern bone (P2). It is a large high-motion joint. The next joint up is the pastern joint. The pastern joint exists between the long pastern bone (P1) and the short pastern bone (P2) and is located between the top of the hoof and the fetlock. Although it is a low-motion joint, the minor degree of motion is very important as it softens weight bearing upon loading of the limb. Ringbone can arise from damage within the joint itself (articular) or from damage to structures such as the joint capsule or ligaments which surround and support the joint (periarticular). Non-articulating ringbone is typically less painful and so considered less serious. Ringbone can begin as non-articulating and advance into articulating and vice versa.
Ringbone generally arises from abnormal and stressful forces placed upon the working joints of the lower limb. Optimal function and movement of the joints necessitates proper alignment and even loading of their working surfaces. Therefore alignment flaws such as toed in or toed out or unnatural hoof angles such as those associated with upright pasterns or long toe-low heels place undue stress on the joints through improper movement dynamics.
It is also equally important to recognize that certain sporting activities predispose a horse to ongoing injury through repetitive strain forces to the lower joints. Such examples include the torque placed upon the limbs of a barrel horse during sharp turns, the sudden hard stops with twisting when a rope horse is dallied up, the landing of a hunter/jumper horse upon unforgiving surfaces, or the concussive forces incurred during the work on pavement of a carriage horse or police mount. Whenever the lower limb is subjected to repetitive or ongoing stress and strain, rotational forces or torque, or concussive forces, the tissues are prone to varying degrees of damage.
If the damage exceeds the body’s abilities to repair itself then disease is a likely result. The rate of damage is compounded when the horse’s body weight exceeds its ideal or when horses travel in poor posture. Work on unforgiving surfaces which are hard, uneven, or overly deep further amplify stress to the joints. Horses under five years of age are particularly vulnerable to excessive stressors and concussive forces. Oftentimes ringbone that seemingly appears later in the horse’s life can be attributed to activities during the early years of a horse’s development when the joints are overtaxed before the horse reaches physically maturity.
The symptoms of ringbone are often insidious and easy to miss in the beginning. The horse may seem reluctant to go forward, refuse certain work, and/or his gait may become short, choppy or shuffling. As with most arthritic conditions the degree of pain can vary from day to day. Symptoms are further confusing as often both legs are affected to varying degrees so the lameness can appear to shift between legs. Commonly heat and swelling can be detected on the pastern and bony ridges may begin to form on the pastern where before it was smooth and sleek. Rest may temporarily resolve the lameness only to return when the horse goes back to work.
A thorough lameness examination by a veterinarian generally involves a historical accounting of the lameness, a clinical evaluation of gait on both hard and soft ground and in straight lines and in circles. Flexion tests, diagnostic nerve blocks, radiographs and more advanced imaging may be undertaken to further define the nature of the ringbone. Ringbone in the coffin joint is much more significant since this is the higher-motion joint.
Once a diagnosis of ringbone is made efforts to manage and preserve the horse’s soundness are multimodal. Maintaining a healthy weight and giving a horse proper rest when needed is important to the healing process. Horses will do best with the consistent low-impact movement such as while on pasture. The moderate movement stimulates circulation and decreases inflammation of the joint and so pain. The amount of activity asked of the horse varies on the degree of ringbone and the tolerance of the individual horse. Oftentimes the job of the horse will need to be reassessed and reassigned in order to reduce wear and tear on the joint. Successful management of ringbone will address the specifics of hoof balance. Although corrective shoeing may be suggested to ease break-over of the lower limb, it is equally important to recognize that improper shoeing practices can be a contributing factor to the development of ringbone since iron shoes strongly influence the movement dynamics of the lower limb.
Medical management is aimed at reducing the pain and inflammation associated with the condition. Anti-inflammatories like phenylbutazone (“bute”) or the new generation of non-steroidal anti-inflammatories firocoxib (Previcox or Equioxx) are used to decrease inflammation associated with acute flare-ups of the condition and to manage horses on a long-term basis. Oral joint supplements that contain glucosamine, chondroitin sulfate, hyaluronic acid, MSM, and other herbal ingredients may benefit some animals. Legend I.V. (intravenous hyaluronic acid) and Adequan I.M. (polysulfated glycosaminoglycan) can also be used to support the joint. Legend addresses the quality of the joint fluid and acts as an anti-inflammatory. Adequan works at the joint surface to heal the cartilage. Alternative therapies such as acupuncture and chiropractic work have varying degrees of efficacy often addressing the compensation patterns in the body caused by the ringbone. Due to the nature of the disease there is tremendous variability with regards to how an individual horse will respond to medications, supplements, injections, regenerative, and complementary therapies.
In some cases of high ringbone the deteriorating joint undergoes a natural progression to the end point whereby the joint collapses and fuses. During the process, the horse is often severely lame. However, once the joint fuses, motion is no longer present and the lameness may resolve to some extent.
Surgical treatment of high ringbone may be an option in certain horses. Essentially the goal of surgery is to complete the body’s attempt of bridging the joint and stop the joint from moving. By preventing motion, joint fusion reduces the pain of ringbone and may allow some horses to return to use. While this procedure involves a major surgery, it offers the possibility of complete return to work and relief from pain. The surgery tends to be more successful on affected hindlimbs than forelimbs. Recently a newer procedure using alcohol to fuse the pastern joint is showing promise and advantage over the surgical technique. Unfortunately, low ringbone remains very difficult to treat and carries a poor prognosis for soundness.