Abscess may, however, form in the interior of the heads of the tibia or lower extremity of the femur without being preceded by the death of any portion of the bone, as is proved by a specimen in the museum of the Richmond Hospital. A child, aged about twelve, had long suffered from chronic disease of the upper portion of the tibia. A chronic symptomatic abscess pointed and opened spontaneously in the popliteal space, and here a fistulous open ing remained discharging a quantity of thin sanious pus. While under treatment for this chronic disease, a sudden attack of acute ar thritis set in, which threatened the patient's life, and amputation was immediately per formed. Upon examination of the knee-joint and of the interior of the bones, which were exposed by a vertical section made from before backwards, an abscess was discovered in the centre of the head of the tibia, capable of con taining a walnut. This communicated with the popliteal abscess, which had long had a fistulous opening in the ham ; but the abscess in the interior of the tibia was now found to have another opening into the cavity of the knee-joint, which had all the appearance of having been quite recent. The matter of the abscess of the tibia having suddenly made its way into the cavity of the knee-joint was the immediate exciting cause of the acute arthritis genu, evidences of which were seen in a layer of lymph which invested the synovial mem brane and the cartilages. The patient ulti mately recovered.
When the chronic form of necrosis affects the tibia and the epiphysis is included in the disease, the knee-joint sometimes remains but little altered, but in other cases remarkable changes in its form take place. The leg is sometimes fully extended, and is even in ad vance of the natural line, but it is more gene rally flexed on the femur, and the tibia is at the same time somewhat curved into the form of an arch, the concavity looking forwards. We have frequently known displacement of the su perior head of the tibia, where it enters into the formation of the knee-joint, to take place back wards towards the popliteal space. This dis placement is usually incomplete. We have examined many living examples of this defor mity, and have had a few opportunities of inves tigating the anatomical changes the joint has been subjected to.
Many circumstances tend to influence the direction in which the luxation may take place. The position in which the limb is preserved during the attack of inflammation of the tibia is one of the most influential. As the limb is generally flexed during the first stage of the disease, the partial luxation backwards will be the one most likely to occur. In these cases, whether the femur or tibia close to the knee be the seat of the necrosis, more or less of effusion takes place into the synovial sac of the knee joint; all the ligaments, of the joint become softened and relaxed ; and the action of the hamstring muscles overcomes the resistance of any remaining structures, and the tibia is dis located partially backwards.
Mr. West, surgeon to the Longford Infir mary, sent to the writer of this article the leg and knee-joint of a man who had long con tended against the consequences of a chronic necrosis of the tibia. There were from time to
time exfoliations of bone, and a continual dis charge of a thin sanious matter which so re duced the strength of. the patient as to render amputation necessary. A cast of the limb, taken by Mr. Smith, and the bone are preserved in the museum of the Richmond Hospital, (figs. 4 and 5,) from which it will be observed that the displacement of the head of the tibia was par tially backwards. This bone was drawn also somewhat upwards, passing inferiorly so far round the condyles of the femur that the arti cular surfaces were almost abandoned. This is the simplest form of displacement of the tibia at the knee-joint from disease which we have noticed as the result of a chronic process of necrosis. We have seen some instances of necrosis in which the whole leg and foot were greatly rotated outwards on the femur, so that the inner ankle was placed directly forwards, and the outer malleolus directly backwards. In these cases the patella is completely dislocated on the outer condyle of the femur (fig. 6), be cause the tubercle of the tibia, in its movement of rotation outwards, carries with it the ligamenium patella, and consequently gradually draws this bone outwards completely over the outer edge of the trochlea of the femur. We have seer at the Richmond Ilospital two similar cases oi this very curious result of necrosis of the tibia In these examples the knee-joint bad partici pated in the inflammation of the contiguous structure, and great deformity of the whole lira was the consequence (fig. 7). The subject o one of these cases (Christopher Tarrer, mt. 30 died of erysipelas, which was idiopathic, ant had no connexion with the deformity. The kne joint was examined, and the patella was fou dislocated outwards, and anchylosed to the o surface of the external condyle of the fe (fig. 6.) The superior extremity of the tibia partially displaced backwards, and was gre deformed and enlarged, particularly the o condyle of this bone, the anterior half of wit' was deeply excavated to receive the condyl the femur; the posterior half of this cond was free and had no bone in contact with but this portion of the tibia and the head of fibula were so much rotated or twisted ott• wards and backwards as to form a very consp • cuous elevation in the lower part of the pop! teal space. The fibula was placed direct behind the tibia. The lateral ligament did iN t exist. The ligameatum patella was great elongated and was directed backwards. The crucial ligaments were also elongated, and instead of crossing each other were untwisted as it were and lay side by side. The carti lages were altogether removed, and when the femur was forcibly separated from the tibia, there were corresponding elevations and de pressions which marked the several points of contact between the bones, in which a species of anchylosis had occurred. The body of the tibia was greatly enlarged and hypertrophied, and round perforations existed in its head, from which sequestra had been discharged.