The exanthemata are frequently fol lowed by joint-tuberculosis—apparently on account of the lowering of the general vitality below the point where the tis sues are capable of resisting the growth of the tubercle bacilli.
Pathology.—In the early stages of hip joint disease there is an hyperemia in the cancellous tissue about the epiphyses where the disease usually begins, in the centre of which a small gray tubercle appears.
The capillaries in the Haversian canals become blocked up with bacilli. An hyperemia is kept up, the trabeculm in the hyperemic area are absorbed, en larged bone-spaces are formed, and fatty degeneration of the bone-cells occurs.
The gray spot in the centre of the hyperemic area increases in size, its centre begins to grow yellow; other sim ilar spots occur and merge into each other; the centre breaks down and be comes a semisolid cheesy mass and may turn into pus.
The blood-vessels in the periphery of the inflamed area often become so blocked that the blood-supply is cut off, and necrosis of a larger or smaller part of the apophysis of the femur results. If all conditions are favorable, the focus may become absorbed or may become cal cified, or else as the focus of disease increases in size it may grow toward the surface of the femur, open outside the joint-cavity, and the case may run a com paratively short course with little or no destruction of the joint, or, as is more usual, it may break into the joint itself, setting up a purulent synovitis.
The synovial membrane becomes in flamed and thickened, the blood-vessels are engorged, an increased serous or sero purulent effusion takes place, and the joint becomes filled with a gelatinous mass, the cartilage becomes eroded, and the bare ends of the bone come in con tact.
If the process becomes less violent, on the contrary, the granulations become firmer and not so pale and gradually give place to fibrous tissue, adhesions forming between the joint-surfaces, scar-tissue taking the place of the granulations, and contraction of the capsule limiting mo tion on the joint.
When the focus of disease is in the ilium, the area of inflammation may ad vance toward the pelvis as well as toward the acetabulum, and in these cases the periosteum lining of the ilium on its inner side becomes much thickened. At
times the entire bottom of the acetab ulum may be absorbed and the head of the femur pass into the pelvis; at other times there is only a small hole through which pus passes to form an abscess which may burst into the bladder or rectum or burrow under the adductor tendons or out on the buttock. Even in this condition recovery is not impossible.
The size of the acetabulum is often increased by the progress of erosion and also by the action of reflex muscular spasm in crowding the head of the femur against the upper rim of the acetabulum. Cases having been reported in which the head of the bone lay inside the pelvis in spite of the limbs' having been kept par allel by plaster of Paris, which had pre vented the occurrence of deformity.
The importance of this fact as bearing on the necessity of traction as well as fixation in the treatment of the disease should not be overlooked.
The erosion of the upper part of the acetabulum accounts for part of the shortening in some cases of hip disease. Retardation of growth may give actual shortening of the femur, and it is not unusual to find that the leg and foot of the affected side are also smaller than their fellows.
If the disease progresses sinuses may burrow from the joint in all directions both inside and outside the pelvis, and later on amyloid changes in the liver and kidneys will be set up or a tubercular meningitis or a general tuberculosis may set in.
Prognosis.—Prognosis in disease of the hip-joint varies very much, being largely determined by the amount of de struction which has taken place before the case conies under observation, the amount of recuperative force possessed by the patient, and the intelligence of home co-operation--the last, perhaps, being the most essential element.
Cases of syphilitic disease ought to give excellent results. if to local protec tion of the joint be added thorough, per sistent antisyphilitic treatment.