#Old-standing Dislocations.#--When, from want of recognition--and, curiously enough, a dislocation is much more liable to be overlooked than would have been thought possible--or from unsuccessful treatment, a dislocation is left unreduced, changes take place in and around the joint which render reduction increasingly difficult or impossible. The rent in the capsule closes upon the neck of the bone, and fibrous adhesions form between muscles, tendons, and other structures that have been torn. The articular cartilage of the head, being no longer in contact with an opposing cartilage, tends in time to be converted into fibrous tissue, and may become adherent to other fibrous structures in its vicinity. By pressing on adjacent structures it may form for itself a new socket of dense fibrous tissue which in time becomes lined with a secreting membrane. When the displaced head lies against a bone, the continuous pressure produces a new osseous socket, from the margins of which osteophytic outgrowths may spring, and as the surrounding fibrous tissue becomes condensed and forms a strong capsule, a new joint results. The occurrence of these changes in the direction of a new ball-and-socket joint is largely dependent on the behaviour of the patient: a vigorous man, anxious to recover the use of the limb, will employ it with a degree of determination and indifference to pain that could not be expected in a sensitive elderly female. The most perfect example of a new ball-and-socket joint, following upon an unreduced dislocation at the hip, that has come under our observation, was in a hunting dog, given one of us by an Australian pupil, who testified that the animal was as fleet with the new joint as it had been with the original one. Meanwhile the cartilage of the original socket is converted into fibrous tissue, which may come to fill up the cavity. Changes resembling those of arthritis deformans may occur. The large blood vessels and nerves in the vicinity may be pressed upon or stretched by the displaced bone, or may be implicated in fibrous adhesions. In course of time they become lengthened or shortened in accordance with the altered attitude of the limb. [Illustration: FIG. 12.--Os Innominatum showing new socket formed after old-standing dislocation. The acetabulum is almost obliterated.] In many cases the new joint is remarkably mobile and useful; but in others, pain, limited movement, and atrophy of muscles render it comparatively useless, and surgical intervention is called for.