[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.
_Treatment._--It is always a difficult problem to determine the date after which it is inadvisable to attempt reduction by manipulation in an old dislocation and no rules can be laid down which will cover all cases. Rather must each case be decided on its own merits, due consideration being had to the risks that attend this line of treatment. The chief of these are: rupture of a large blood vessel or nerve that has formed adhesions with the displaced bone, or has become shortened in adaptation to the altered shape or length of the limb; tearing of muscles or tendons, or even of skin; fracture of the bone, especially in old people; and separation of epiphyses in the young.
Before carrying out the manipulations appropriate to the particular dislocation, all adhesions must first be broken down; and during the proceedings no undue force is to be employed. The first attempt at reduction may fail, and yet subsequent efforts, at intervals of a few days, may ultimately prove successful; the vigorous traction and twisting of the soft parts, matted together as they are by scar-tissue, causes reactive changes in the vessels and tissues which render them more liable to yield on subsequent attempts at reduction. In old people, and where there is an absence of suffering from pressure on nerves or vessels, it may be wiser to leave the dislocation unreduced, and strive rather by massage and movement to obtain a useful variety of false joint. If the conditions are otherwise, it may be better to improve the function of the limb by an _open operation_. Tight ligaments and other structures are divided, and the socket is cleared out. If reduction is still impossible, a partial excision may be performed and a flap of fascia lata introduced to prevent ankylosis (arthroplasty). In the case of the hip, the dislocation may be left alone and the femur divided below the trochanter, especially if there is pronounced flexion.