This condition is analogous to that already described as capped elbow. It consists of a prominent - sometimes pendulous - enlargement, the result of an inflamed and swollen state of the skin and subcutaneous connective tissue. It differs, however, from the last-named affection in the less frequent formation of matter within it and a greater disposition to become hard and callous. It is more commonly seen in cart-horses than in the lighter breeds, and in cattle the growth often attains to an immense size.
Capped knee is invariably the result of violence applied to the part, mostly following upon a fall or repetition of falls, when the skin and parts beneath become contused and swollen. In some horses it results from a habit of falling on the knee in the act of lying down, while others contract it by striking the manger or the log at the end of the halter in the act of pawing. Kicks and blows may also induce it.
In some cases capped knee is of slow growth, especially where the part continues to receive a succession of slight contusions, as in some of the causes referred to above. When this is so, the enlargement usually presents the appearance and character of a solid organized tumour, resulting from the repeated irritation to which it has been exposed. When it originates suddenly from a severe blow, it may assume the form of a cyst and contain a quantity of yellow or blood-stained fluid, or should the injury be sufficiently severe to excite acute inflammation in the skin and underlying tissue an abscess may result.
Fig. 385. - Pad to prevent Capped Elbow.
From what has been said, it will be understood that the swelling constituting "capped knee" is a disease of the skin and subcutaneous tissue, and has no reference whatever to another form of enlargement in front of the joint resulting from a distension of the sheath of the extensor tendon of the metacarpus. In the disease in question the swelling when of slow growth is hard and callous; when of more rapid formation it assumes the form of a fluctuating swelling which may or may not be attended with pain. In all cases where an abscess develops, the part is hot and painful, and in a less degree pain is manifested for a while where the tissues become infiltrated with blood-stained fluid only. The latter condition may assume a chronic form and continue long after all soreness has subsided.
Where indications of chronic enlargement of the knee appear as a result of bruising in the act of lying down, the horse should be placed in a loose-box and be provided with a thick bed of peat-moss. This alone in such cases is sufficient to put an end to the trouble. Where, however, the growth has become considerable and undergone organization, its complete removal is impossible save by a surgical operation. Some reduction, however, may be effected in it by a course of blistering, and its further development will be prevented by protecting the animal from a repetition of the injury that brought it on.
If the enlargement is found to contain a watery fluid, the contents must be drawn off by the aspirator and a little tincture of iodine injected into the sac. This having been done, a bandage should be tightly bound round the knee in order to prevent its refilling, and at the same time to induce the disconnected skin to unite again to the parts beneath. For this purpose the horse should be kept tied to the rack or placed in slings and prevented from lying down.
Where the swelling is hot and painful, and there is reason to suspect the existence of an abscess, hot fomentations should be applied to the part, and so soon as any indications of "pointing" appear it should be freely opened with the knife and free vent given to the contained "matter". The sac should then be well syringed out with carbolic solution or some equally efficient disinfectant, and the wound treated on the antiseptic system. At the same time it is to be observed that the displaced skin of the knee forming the wall of the abscess must be bound down by means of a bandage, as previously suggested, and the horse kept in the standing posture.