Tuberculous Disease
Tuberculous disease of joints results from bacillary infection through the arteries. The disease may commence in the synovial membrane or in the marrow of one of the adjacent bones, and the relative frequency of these two seats of infection has been the subject of considerable difference of opinion. The traditional view of König is that in the knee and most of the larger joints the disease arises in the bone and in the synovial membrane in about equal proportion, and that in the hip the number of cases beginning in the bones is about five times greater than that originating in the membrane. This estimate, so far as the actual frequency of bone lesions is concerned, has been generally accepted, but recent observers, notably John Fraser, do not accept the presence of bone lesions as necessarily proving that the disease commenced in the bones; he maintains, and we think with good grounds, that in many cases the disease having commenced in the synovial membrane, slowly spreads to the bone by way of the blood vessels and lymphatics, and gives rise to lesions in the marrow.
Morbid Anatomy.—Tuberculous disease in the articular end of a long bone may give rise to reactive changes in the adjacent joint, characterised by effusion and by the extension of the synovial membrane over the articular surfaces. This may result in the formation of adhesions which obliterate the cavity of the joint or divide it into compartments. These lesions are comparatively common, and are not necessarily due to actual tuberculous infection of the joint.
The infection of the joint by tubercle originating in the adjacent bone may take place at the periphery, the osseous focus reaching the surface of the bone at the site of reflection of the synovial membrane, and the infection which begins at this point then spreads to the rest of the membrane. Or it may take place in the central area, by the projection of tuberculous granulation tissue into the joint following upon erosion of the cartilage ([Fig. 156]).
Fig. 156.—Section of Upper End of Fibula, showing caseating focus in marrow, erupting on articular surface and infecting joint.
Changes in the Synovial Membrane.—In the majority of cases there is a diffuse thickening of the synovial membrane, due to the formation of granulation tissue, or of young connective tissue, in its substance. This new tissue is arranged in two layers—the outer composed of fully formed connective or fibrous tissue, the inner of embryonic tissue, usually permeated with miliary tubercles. On opening the joint, these tubercles may be seen on the surface of the membrane, or the surface may be covered with a layer of fibrinous or caseating tissue. Where there is greater resistance on the part of the tissues, there is active formation of young connective tissue which circumscribes or encapsulates the tubercles, so that they remain embedded in the substance of the membrane, and are only seen on cutting into it.
The thickened synovial membrane is projected into the cavity of the joint, filling up its pouches and recesses, and spreading over the surface of the articular cartilage “like ivy growing on a wall.” Wherever the synovial tissue covers the cartilage it becomes adherent to and fused with it. The morbid process may be arrested at this stage, and fibrous adhesions form between the opposing articular surfaces, or it may progress, in which case further changes occur, resulting in destruction of the articular cartilage and exposure of the subjacent bone.
In rare instances the synovial membrane presents nodular masses or lumps, resembling the tuberculous tumours met with in the brain; they project into the cavity of the joint, are often pedunculated, and may give rise to the symptoms of loose body. The fringes of synovial membrane may also undergo a remarkable development, like that observed in arthritis deformans, and described as arborescent lipoma. Both these types are almost exclusively met with in the knee.