HYGROMA OF THE KNEE.
This condition is very common in bovines, a fact explained by the manner in which these animals rise. Whilst the hind limbs are being lifted, the entire burden of the body weight is transmitted to the knees and the tissues covering them; so that, if the ground is rough, the skin may be sufficiently displaced to produce laceration of the subcutaneous connective tissue, serous effusion in the layers of connective tissue, and the immediate production of an hygroma beneath the skin and in front of the synovial sheaths of the extensor tendons.
Hygroma is principally caused by falls on the knees, roughness of the stable floor, prolonged decubitus during the course of a serious disease, or after an attack of foot-and-mouth disease.
Hygromas may be no larger than a turkey’s egg or a man’s clenched fist, but sometimes assume the dimensions of a child’s head. Calcification and ossification of the walls and cornification of the skin are commonest in old hygromas of the knee.
The sensibility and uniform fluctuation make mistakes in diagnosis difficult. The condition can only be confused with distension of the synovial sheath of the extensor metacarpi magnus; but this (synovial) swelling extends in the same direction as the tendon, i.e., vertically, attains the lower third of the radius, and is broadest above. Hygromas must also be distinguished from tumours. Moussu only mentions a single case of this kind, the tumour being very slightly bosselated and, naturally, revealing no fluctuation.
The prognosis is not grave, though the condition may prove troublesome, because the original injuries may be continued even during treatment and prevent recovery.
Fig. 26.—Hygroma of the knee. The skin has undergone conversion into a substance resembling horn.
Treatment. Success rarely follows cold applications or blistering, which are only of value at the commencement. It is better to puncture the cavity aseptically, remove the fluid contents, and fire the growth in points. Free opening of the lowest portion of the swelling is followed by discharge of liquid, but almost inevitably by infection at a later stage, and by suppuration. Recovery certainly may occur, a slight thickening of the anterior surface of the knee remaining; but the process is often very prolonged. Some authors prefer to pass a seton or drain vertically through the swelling. The results are identical with those following free opening and drainage, suppuration being unavoidable.
If the animal be sufficiently valuable to warrant surgical intervention, the entire hygroma, together with its indurated wall, may be excised. An elliptical fragment of skin is removed from the front of the swelling, and the whole mass separated by dissecting away or tearing through the connective tissue. Considerable care is necessary to avoid injuring the synovial sheaths of the extensor tendons. This treatment, which is only applicable in valuable animals, is completed by firmly suturing the lips of the wound, and applying an antiseptic surgical dressing or a plaster bandage similar to that used in operating on broken knees in horses.[[1]] The animal must be prevented from lying down until the wound has firmly united.