Osteochondritis appears to consist in a suppurative ostitis affecting the epiphyseal end of the bone. The layer of cartilage preparing for ossifica tion becomes thickened to three or four times its natural width, and gets soft. This increase in width is due to excessive prolifera tion Of the cartilage cells, which assume much the shape and size of the round granulation cells of syphilitic gummata. At the same time the intercellular substance is diminished. The cartilage which is actually undergoing ossification is thickened, and shows on section a broad wavy line. By the microscope the osteoblasts are found to be replaced more or less completely by small granulation cells or spindle-shaped elements. After a time destructive changes set in in the bony tissue. Dr. Parrot de scribes a " gelatiniform softening," in which the bone is replaced by a soft, rather transparent material of a yellowish or brownish colour. After death, when the bone is dry, a cavity is left. The cancellous structure is also infiltrated with purulent watery fluid, so that the lamella disappear and leave a fibro:vascular network filled with the same fluid. According to Wegner, a characteristic feature of this osseous disease is the protru sion of bundles of fibrous tissue along the course of the blood-vessels. These bundles pass through the cartilage, the calcifying layer, and the processes of spongy bone, and penetrate deeply into the cancellous tissue of the shaft.
As a consequence of this lesion the epiphyses with the ossifying layer may separate from the shaft of the bone. Suppuration is then set up, an abscess forms, and the pus escapes into the surrounding tissue by penetrat ing the periosteum. The joint itself is not involved as a rule ; but Dr. Lees has reported a case in which the left elbow-joint and both knee-joints became filled with pus.
Periosteogenesis is more common than osteochondritis. It attacks par ticularly the humerus and the tibia ; and gives rise to symptoms, recog nised during life, which will be afterwards described.
An osseous lesion, due probably to changes similar in character to those described above, and called dactylitis, may attack the bones of the hands and feet. Dr. Taylor, of New York, has contributed much to our knowledge of this affectioli. According to this author, the disease begins either in the fibrous tissue surrounding a joint or in the periostetun. In the first form slight enlargement is seen of one or more toes or fingers— either of the whole length, as occurs in the toes, or of one or more pha langes, as is seen in the case of the fingers. The process is slow and is accompanied by little or no pain, although the swelling interferes with the play of the joint. The second form is most frequently seen in the fingers.
One or more of the phalanges becomes evenly rounded or fusiform. When the first phalanx is attacked, it usually assumes the shape of an acorn. The metacarpal and metatarsal bones may be also affected in the same way. In all cases, as a rule, the tendency is to resolution. Still, sometimes, if the enlargement is great, the part is exposed to accidental injury. The skin then becomes swollen, red, and tense ; ulcerates or is incised, and discharges a soft, cheesy detritus mixed with pus. Limited necrosis may follow and lead to shortening of the finger. Dactylitis is usually seen in very young children, but it may be a later symptom. The number of fingers affected varies. Dr. Taylor mentions a case in which all the phalanges of both hands were involved.
The bones of the skull may be affected by the two forms of disease which attack the bones. Gelatiniform softening is comparatively rare, but is sometimes found in very young infants. IC'begins beneath the pericranium but does not penetrate deeply into the bone, so that it rarely reaches the Jura matey. After death the bone has a worm-eaten appear ance. This form cannot be diagnosed during life. The osteoid growths are only found in older children. At first they always occupy the same situation, viz., the frontal and parietal bones surrounding the anterior fon tanelle. Sometimes they are also seen in the temporal bones, but are never found, unless the disease be exceptionally severe, in the orbital plates or the occipital bone. As they grow they produce a very character istic deformity of the skull. The fontanelle comes to be surrounded by four elevations, which are separated by two furrows intersecting one another in the form of a cross—the one transverse, the other antero-posterior. These osteophytes are usually spongy and porous, but they may become hard and smooth like normal bone tissue. They sometimes reach an inch and a quarter in thickness.
In addition to the above purely syphilitic changes, local thinning of the bone, called cranio-tabes, is often found. This condition, which is a thin ning or even perforation in certain spots of the cranial bones, was until lately considered to be exclusively a symptom of rickets. It is due to di rect pressure upon the bones of the skull by the brain within and the pillow without, and is found especially in the occipital bone. It may be present in rickets where no trace of syphilis can be discovered, but is most common in cases where there is a distinct syphilitic taint.' It is difficult to say with certainty at what age a child becomes liable to syphilitic disease of bone. Gelatiniform softening and osteochondritis generally occur early, beginning before the sixth month, and it is probable .