(a) Simple Or Serous Arthritis.
With an attack of simple synovitis it may be always assumed that the changes commenced in the synovial membrane, communicate themselves more or less readily to the surrounding tissues, and are not confined to the synovial membrane alone. We may thus have the inflammatory phenomena asserting themselves in the surrounding ligaments, in the periosteum, in the bone, and in the articular cartilages. It depends, in fact, upon the severity of our case whether we call it synovitis or arthritis. The two conditions merge so the one into the other that no hard-and-fast rule may be laid down whereby they may with certainty be differentiated. Such symptoms, therefore, as we have given for synovitis may be also read as indicating a condition of simple arthritis. The course of the case will be very similar, and the treatment to be followed identical with that just given.
(b) Acute Arthritis.
Causes. - An attack of acute arthritis may commence with the affection of the synovial membrane, and spread from that to the other structures. In other cases the disease of the synovial membrane, and after it the disease of the joint, may be secondary to diseases commencing in the structures around the joint. This affection may therefore follow on a case of acute coronitis, a case of suppurating corn, a case of quittor, a severe case of tread, or may attend a case of laminitis.
Symptoms. - In our cases we get very little beyond a magnification of such symptoms as we have described under acute synovitis. The heat and the pain is perhaps greater, and the lameness more marked. It is rather to the constitutional disturbance we must look, however, for a confirmation of our opinion that arthritis is in existence. This is always severe, and of an acute febrile nature. The pulse is fast, thin, and thready, the respirations enormously increased, and the temperature high. The appetite is in abeyance, the animal quickly becomes what is termed 'tucked-up,' or greyhound-like, in the body, and patchy perspirations break out about him. The limb is held with the joints all semiflexed, and severe and intense throbbing pains are indicated by the frequent pawing movements the animal makes in the air. Manipulation of the foot is resented, and the agonizing intensity of the pain so caused is shown by the drawn and haggard appearance of the eyes.
In a favourable case the symptoms from now onwards may gradually subside. The appetite returns, the breathing and other signs of disturbance show a return to the normal, weight is placed on the limb, and resolution slowly but surely takes place. In many of these, our favourable cases, however, resolution is incomplete, and recovery only takes place at the expense of anchylosis of the joint, a condition we shall refer to later.
In unfavourable cases, and these unfortunately are only too common, the condition terminates in suppuration.
(c) Purulent Or Suppurative Arthritis.
Definition. - By this term we indicate an arthritis complicated by the formation of pus within the joint.
Causes. - The organisms of pus may infect the joint by extension of a suppurating process from without. For example, in the case of a suppurating corn, in quittor, in tread, or in the case of a suppurating wound caused by a prick, the pus formed may in many instances be very near the capsular ligament of the articulation. Under such circumstances, unless there is a free and unhindered flow of the pus from an outside opening, inroads will be made by it upon the thin capsule. The latter is quickly penetrated, and pus is admitted to the interior of the joint.
In other cases infection of the joint may proceed from within, from a poisoned state of the blood-stream. The condition occurs, for instance, in bad attacks of laminitis. We ourselves, too, have seen two cases where suppuration of the pedal articulation occurred in the septic pyaemia of foals, a disease known commonly as 'joint-ill,' and characterized by an infected state of the circulation. Cases have also come under our notice where this condition has resulted from slight injuries in the region of the insertion of the extensor pedis inflicted by the animal himself when galloping away.
Perhaps, however, the most common cause of suppurative arthritis in the foot is direct penetration of the articulation in the case of pricks. The penetrating object is nearly always dirty - bacterially dirty, at any rate - and suppuration only too readily commences. Even should such a wound be inflicted by an aseptic body, infection would quickly ensue as a result of the wound gathering dirt from the ground, or even from admission to the joint of impure and bacilli-laden air.