Fig. 24.—Luxation backwards and inwards of the femoro-tibial joint. (From a photograph by Professor Besnoit.)
Symptoms. The most frequent condition is backward luxation of the upper extremity of the tibia. Movement becomes difficult, the limb is held rigidly, and all the lower part of the leg is extended. None of the joints can be flexed. The leg is dragged forward, without the animal being able to place the foot flat on the ground, and the claws are trailed over the litter or the toe grazes the soil.
On local examination the stifle is seen to be deformed. The lower extremity of the femur and the patella appear prominent. The upper part of the tibia is thrust backwards, and seems to have disappeared, leaving a depression below the femoro-patellar region. The muscles forming the back of the thigh at this level are thrust out of position, and appear to project abnormally.
Viewed from behind, the inner line of the thigh appears more or less convex when the upper extremity of the tibia is luxated inwardly. On local examination the displacement of the bones can be readily detected. In luxation forwards the prominence of the stifle is caused by the summit of the tibial crest and by the patella, whilst the lower extremity of the femur cannot be felt. In outward luxation the upper extremity of the tibia forms an abnormal prominence, above which a horizontal digital depression appears.
Diagnosis. Provided that the examination is made soon after the occurrence of the accident, little difficulty will be found in coming to a conclusion, but the diagnosis necessitates more care when examination is deferred for two or three days, because extensive effusion then exists. Luxations or subluxations of tuberculous origin are generally consecutive to old-standing destructive tuberculous arthritis.
The prognosis is grave—firstly, because reduction is difficult; and, secondly, because it is often impossible to maintain the reduction and to preserve complete immobilisation of the injured joint.
Treatment should not be undertaken except in young animals which have not yet attained full development.
In attempting to reduce outward or inward luxation of the tibia the animal should be cast on the side opposite to the lesion. Counterextension is practised by passing a length of webbing around the limb in the region of the groin; extension in the direction of the length of the femur by means of a loop of webbing fixed to the cannon bone: the operator uses both hands in endeavouring to replace the head of the tibia.
In forward luxation of the tibia counter-extension is effected by means of a loop of webbing passed above the hock and drawn forward. Extension is made backwards in an oblique direction, the operator again being left free to effect reduction with both hands.
Reduction of backward luxation of the tibia is still more difficult, in consequence of the contraction of the mass of muscle at the back of the thigh.