_Bleeder's knee_, _Charcot's disease_, _hysterical knee_, and _loose bodies_ in the joint have already been described.
There is a common synovial cavity for the ankle and the inferior tibio-fibular joints. The epiphysial cartilage of the tibia lies above the level of this synovial cavity, but that of the fibula is included within its limits (Fig. 93). The talus is related to three articulations--the ankle above, the talo-navicular joint in front, and the calcaneo-taloid joint below. The tendon sheaths, especially those of the peronei and of the tibialis posterior, are liable to be infected by the spread of infective disease from the joint.
#Tuberculous Disease.#--Tuberculous disease at the ankle is met with at all ages. In the majority of cases the disease affects both bone and synovial membrane. Gross lesions in the bones are comparatively rare, and are chiefly met with in the head or neck of the talus.
_Primary synovial disease_ usually exhibits the features of white swelling, projecting beneath the extensor tendons on the dorsum, and, posteriorly, filling up the hollows on either side of the tendo Achillis and below the malleoli (Fig. 126). The foot may retain its normal attitude, or the toes may be pointed and adducted. The calf muscles are wasted, there is little complaint of pain, and the movements of the joint may be so little interfered with that the patient can walk without a limp. When the disease involves the articular surfaces, there is pain and sensitiveness, the movements are restricted or abolished, and the patient is unable to put the foot on the ground.
[Illustration: FIG. 126.--Tuberculous Disease in a man æt. 35, of six weeks' duration.]
_A primary focus in the bone_ causes localised pain and tenderness, and a limp in walking, but the first sign may be the formation of abscess or the rapid development of articular symptoms. In such cases skiagrams afford valuable information.
Abscess formation is an early and prominent feature, whether the disease is of osseous or synovial origin, and sinuses are liable to form around the joint. Outlying abscesses and sinuses are usually the result of infection of the tendon sheaths in the neighbourhood.
_Diagnosis._--When teno-synovitis occurs independently of disease of the ankle, the swelling is confined to one aspect of the joint. In sarcoma of the lower end of the tibia, the swelling lacks the uniform distribution of that met with in joint disease. In Brodie's abscess of the lower end of the tibia there may be swelling of the ankle, but there is an area of special tenderness on percussion over the bone.