Short, upright, pasterns receive greater concussion during fast travel on hard roads than do the longer more sloping and well formed extremities. Those who are advocates of the theory that this type of osteitis with its complications has its origin in the articular portion of the joint, claim that the upright pastern constitutes an important tendency toward ringbone. Howbeit, ringbone is an active, serious and frequent cause of lameness and it affects animals of all ages and occurs under various conditions. Horses having good conformation and kept at work wherein no great amount of strain is put upon these parts, are occasionally victims of this affection.
Classification.—The arrangement employed by Moller is intensely practical and logical. He considers ringbone as articular, periarticular, rachitic and traumatic. A mode of classification that is common and in a practical way, good, is, high and low ringbone. When prognosis is considered, for instance, it is very convenient to state that the chances for recovery are much better in high ringbone than in low ringbone. The classification of Moeller will be followed here.
[Illustration: Fig. 17—Phalangeal exostoses.]
Symptomatology.—In all forms of incipient ringbone except rachitic, the first manifestation of its existence, or of injury to the ligaments in the region of the pastern joint which causes periostitis, or affections of the articular portions of the proximal inter-phalangeal joint, is lameness. Lameness which typifies ringbone is of the supporting-leg variety and by compelling the subject to step from side to side, marked flinching is observed, especially in periarticular ringbone; causing the affected animal to turn abruptly on the diseased member, using it as a pivot, likewise accentuates the manifestation. In fact, many subjects that exhibit no evidence of locomotory impediment while walking or trotting in a straight line on a smooth road surface, will manifest the characteristic form of lameness from ringbone when the aforementioned side to side movement is performed.
When the manner in which pain is occasioned is considered, it will be understood why lameness is intermittent in the early stages of this affection and may even be unnoticed by the driver. An animal may travel on a smooth road without giving evidence of any inconvenience, but as soon as a rough and irregular pavement or road surface is reached, will limp. As the subject is driven farther on level streets the lameness may disappear. This intermittent type of lameness may continue until there is developed a large exostosis, or until articular involvement causes so much distress during locomotion that lameness is constant. On the other hand, resolution may occur during the stage of periosteal inflammation, or, an exostosis forms which causes no interference with function.
[Illustration: Fig. 18—Rarefying osteitis in chronic ringbone and ossification of lateral cartilages.]