Startings at night are to be regarded as an indication that there is progressive disease involving the articular surfaces.

The formation of extra-articular abscess may take place early, or it may not occur till long after the disease has subsided. The abscess may develop so insidiously that it does not attract attention until it has attained considerable size, especially when associated with disease of the spine, pelvis, or hip. The position of the abscess in relation to different joints is fairly constant and is determined by the anatomical relationships of the capsule and synovial membrane to the surrounding tissues. The bursæ and tendon sheaths in the vicinity may influence the direction of spread of the abscess and the situation of resulting sinuses. When the abscess is allowed to burst, or is opened and becomes infected with pyogenic bacteria, there is not only the risk of aggravation of the disease and persistent suppuration, but there is a greater liability to general tuberculosis.

The sinuses may be so tortuous that a probe cannot be passed to the primary focus of disease, and their course and disposition can only be demonstrated by injecting the sinuses with an emulsion of bismuth and taking X-ray photographs.

Tuberculous infection of the lymph glands of the limb is exceptional, but may follow upon infection of the skin around the orifice of a sinus.

A slight rise of temperature in the evening may be induced in quiescent joint lesions by injury or by movement of the joint under anæsthesia, or by the fatigue of a railway journey. When sinuses have formed and become infected with pyogenic bacteria, there may be a diurnal variation in the temperature of the type known as hectic fever ([Fig. 11]).

Relative Frequency of Tuberculous Disease in Different Joints.—Hospital statistics show that joints are affected in the following order of frequency: Spine, knee, hip, ankle and tarsus, elbow, wrist, shoulder. The hip and spine are most often affected in childhood and youth, the shoulder and wrist in adults; the knee, ankle, and elbow show little age preference.

Clinical Variations of Tuberculous Joint Disease.—The above description applies to tuberculous joint disease in general; it must be modified to include special manifestations or varieties.

When the main incidence of the infection affects the synovial membrane, the clinical picture may assume the form of a hydrops, or of an empyema in which the joint is filled with pus. More common than either of these is the well-known white swelling or tumor albus (Wiseman, 1676) which is the clinical manifestation of diffuse thickening of the synovial membrane along with mucoid degeneration of the peri-synovial cellular tissue. It is well seen in joints which are superficial—such as the knee, ankle, elbow, and wrist. The swelling, which is the first and most prominent clinical feature, develops gradually and painlessly, obliterating the bony prominences by filling up the natural hollows. It appears greater to the eye than is borne out by measurement, being thrown into relief by the wasting of the muscles above and below the joint. In the early stage the swelling is elastic, doughy, and non-sensitive, and corresponds to the superficial area of the synovial membrane involved, and there is comparatively little complaint on the part of the patient, because the articular surfaces and ligaments are still intact. There may be a feeling of weight in the limb, and in the case of the knee and ankle the patient tires on walking and drags the leg with more or less of a limp. Movements of the joint are permitted, but are limited in range. The disability is increased by use and exertion, but, for a time at least, it improves under rest.

If the disease is not arrested, there follow the symptoms and signs of involvement of the articular surfaces.

Influence of Tuberculous Joint Disease on the General Health.—Experience shows that the early stages of tuberculous joint disease are compatible with the appearance of good health. As a rule, however, and especially if there is mixed infection, the health suffers, the appetite is impaired, the patient is easily tired, and there may be some loss of weight.