"High ringbone" refers to the development of chronic pastern joint arthritis, with bony deposits around the pastern (proximal interphalangeal) joint. The pastern joint is the joint between P1 (the long pastern bone) and P2 (the short pastern bone). "Low Ringbone", on the other hand, is addressed as a separate diagnosis and refers to arthritis of the coffin (distal interphalangeal) joint.

The pastern joint is not very tolerant of trauma. A sprain of the pastern joint might occur and involve tear of joint capsule and/or supporting ligaments of the joint. Joint inflammation (arthritis) starts, and a cycle of damage of the joint begins. The pastern joint is unique in how it reacts by laying down large quantities of bone in an "attempt to stabilize" itself. This results in a large collar of bone and ongoing pain, inflammation and increased cartilage destruction within the joint, and increased bone production around it.

Chronic pastern arthritis is a common cause of debilitating lameness in horses of every type and discipline. It is seen more commonly in horses predisposed to injury because of poor lower limb conformation and thus uneven forces on the joint causing uneven cartilage wear. The process can begin as a single traumatic injury to the supporting ligaments and/or the joint itself. An accident like this can happen to any horse, regardless of conformation.

In advanced cases, high ringbone is easy to diagnose on visual analysis. The pastern is enlarged, with an obvious donut of bone surrounding the joint. Early pastern injury, prior to this obvious deposit of bone, may require vet diagnostics like diagnostic anesthesia, radiography and ultrasound. Radiography is very commonly used to determine the severity of chronic pastern arthritis.

Treatment of this painful condition often involves procedures that result in fusion (in most cases, fusion of the low motion pastern joint does not take place on its own). Complete fusion of P1 and P2 - resulting in loss of the joint - alleviates the pain but results in slightly less range of motion in the lower limb. Since the pastern joint only contributes a small amount to range of motion and horses can still usually function, and even perform athletically. Thus, fusion may be recommended as the only course of treatment. Otherwise, there is no "cure' for pastern arthritis once it starts, only management.

Horses with high ringbone can also develop low ringbone (in the coffin joint), which is a comparatively more serious disease process with a worse prognosis.