Syphilitic affections of joints are comparatively rare. As in tuberculosis, the disease may be first located in the synovial membrane, or it may spread to the joint from one of the bones.
In acquired syphilis, at an early stage and before the skin eruptions appear, one of the large joints, such as the shoulder or knee, may be the seat of pain—arthralgia—which is worse at night. In the secondary stage, a synovitis with serous effusion is not uncommon, and may affect several joints. Syphilitic hydrops is met with almost exclusively in the knee; it is frequently bilateral, and is insidious in its onset and progress, the patient usually being able to go about.
In the tertiary stage the joint lesions are persistent and destructive, and result from the formation of gummata, either in the deeper layers of the synovial membrane or in the adjacent bone or periosteum.
Peri-synovial and peri-bursal gummata are met with in relation to the knee-joint of middle-aged adults, especially women. They are usually multiple, develop slowly, and are rarely sensitive or painful. One or more of the gummata may break down and give rise to tertiary ulcers. The co-existence of indolent swellings, ulcers, and depressed scars in the vicinity of the knee is characteristic of tertiary syphilis.
The disease spreads throughout the capsule and synovial membrane, which becomes diffusely thickened and infiltrated with granulation tissue which eats into and replaces the articular cartilage. Clinically, the condition resembles tuberculous disease of the synovial membrane, for which it is probably frequently mistaken, but in the syphilitic affection the swelling is nodular and uneven, and the subjective symptoms are slight, mobility is little impaired, and yet the deformity is considerable.
Syphilitic osteo-arthritis results from a gumma in the periosteum or marrow of one of the adjacent bones. There is gradual enlargement of one of the bones, the patient complains of pains, which are worst at night. The disease may extend to the synovial membrane and be attended with effusion into the joint, or it may erupt on the periosteal surface and invade the skin, forming one or more sinuses. The further progress is complicated by the occurrence of pyogenic infection leading to necrosis of bone, in the knee-joint, for example, the patella or one of the condyles of the femur or tibia, may furnish a sequestrum. In such cases, anti-syphilitic treatment must be supplemented by operation for the removal of the diseased tissues. In the knee, excision is rarely necessary; but in the elbow it may be called for to obtain a movable joint.
In inherited syphilis the earliest joint affections are those in which there is an effusion into the joint, especially the knee or elbow; and in exceptional cases pyogenic infection may be superadded, and pus form in the joint.
In older children, a gummatous synovitis is met with of which the most striking features are: its insidious development, its chronic course, symmetrical distribution, freedom from pain, the free mobility of the joint, its tendency to relapse, and its association with other syphilitic stigmata, especially in the eyes. The knees are the joints most frequently affected, and the condition usually yields readily to anti-syphilitic treatment without impairment of function.