This luxation is also found as a purely accidental occurrence in animals which have suffered from falls and from slipping of the hind limbs backwards or sidewards, as occasionally follows awkward leaping movements. The slipping outwards of the limbs, which causes this form of luxation, is comparatively easy, because of the absence of the pubio-femoral ligament. The accident may also be followed merely by subluxation, that is to say, tearing of the inner portion of the capsular ligament and rupture of some portion of the adductor muscles of the thigh without rupture of the interosseous fibres, the head of the femur not quitting the cotyloid cavity. This accident occurs in stables with smooth, slippery floors, and in railway trucks. It may affect one side or both. The latter condition is exceptional.
Finally, luxation may be either complete (in which case the capsular and interosseous ligaments are both ruptured) or incomplete. In the former case, the head of the femur becomes displaced upwards and forwards towards the great sciatic notch, more rarely backwards in the direction of the ischium, and in exceptional cases downwards and inwards below the pubis into the foramen ovale.
Symptoms. The symptoms vary, depending on whether the luxation is of the spontaneous, progressive order or, on the contrary, is accidental. In progressive luxation, the animals are able to rise and walk with difficulty. The affected limb swings when the animal is advancing, not as though it were paralysed, but simply as though displaced at its upper part. Pain is exhibited when weight is placed on the limb, and there is difficulty in movement. The limb appears shorter than its neighbour when the animal stands on it, and the prominence representing the trochanter is more marked. When a false joint has formed, the limb is rigid, is moved stiffly and abducted, and the stride is shortened.
Fig. 21.—Accidental luxation of the hip joint.
In accidental luxations, either of one or both limbs, the attitude assumed by the animal is often characteristic. One of the limbs is extended at right angles to the longitudinal axis of the body, and sometimes both limbs assume this position, an attitude which would be absolutely impossible under normal conditions. The animal cannot rise. It lifts the front part of the body by rising on its knees, but the hind quarters do not follow. The ruptured adductor muscles are unable to bring and hold the limb parallel to the longitudinal axis of the body; the abductors act unopposed, and at the moment when the animal makes its greatest effort to rise the limb (or limbs) is carried outwards and the body comes to the ground on the udder or groin.
Inspection discovers a depression where the great trochanter should be. On applying the open hand over the hip joint, whilst an assistant who grasps the pastern moves the limb in different directions, one can feel and hear, in spite of the mass of muscle covering the part, a modified crepitation due to sero-sanguinolent effusion in and around the joint. This crepitation can also be detected by pushing the hand as high up as possible on the internal surface of the thigh, and thus exploring the neighbourhood of the luxation.
Diagnosis. The position which the animal assumes when one endeavours to make it rise is characteristic. Diagnosis of progressive luxation, however, is more difficult.
Prognosis. The prognosis is extremely grave; for, even though reduction can be effected, one is practically unable to ensure that the parts shall remain in position.
Treatment. Treatment comprises reduction of the luxation and fixation of the parts. Reduction can be effected without very much difficulty by casting the animal on the affected side, placing a block of wood, or a pail, between the thighs, and manœuvring the limb in the desired direction. As, however, subluxation is the condition most commonly seen, there is frequently no reduction to effect. Moreover, fixation of the joint after reduction is almost impossible in such heavy subjects, and luxation is very liable to recur. From an economic standpoint, slaughter is advisable or imperative.