Quittor is a chronic, septic condition of one of the collateral cartilages of the distal phalanx characterized by necrosis of the cartilage and one or more sinus tracts extending from the diseased cartilage through the skin in the coronary band region. It is seldom encountered today but was common in working draft horses in the past. Quittor usually follows injury to the limb on the medial or lateral aspect of the lower pastern (immediately proximal to the coronary band, over the proximal extent of the cartilage), by means of which infection is introduced into the traumatized collateral cartilage. This leads to localized sepsis or abscessation of the cartilage. The cartilage may also become infected through a quarter crack (see below). The first sign is an inflammatory swelling over the region of the collateral cartilage, which is followed by sinus formation and intermittent drainage. During the acute stage, lameness occurs.
Surgery to remove the diseased tissue is required, but care must be taken not to enter the distal interphalangeal joint. Local or parenteral antibiotic therapy (or both) without surgery is likely to fail. In the absence of any therapy, poor drainage, cartilage necrosis, and recurrent abscessation lead to chronic lameness and extension to deep structures. The prognosis is unfavorable if the disease progresses to involve the distal interphalangeal joint.