Occasionally a bit of cartilage gets broken off in the knee-joint and wedged between the bones, so that the joint cannot be straightened. This is [dislocation of the semilunar cartilage] and necessitates an operation for removal of the piece. The cartilage will eventually be replaced by fibrous tissue and in a few months the leg will be all right. Dislocation of the knee is rare, though it may occur in any direction. Often the bursæ of the joint are irritated, as by kneeling to scrub floors, and bursitis or housemaid’s knee results. Fracture of the patella may be caused by muscular traction or by direct violence, and is generally repaired by making an incision and sewing the parts of the bone together. Tumor albus or white swelling is tuberculosis of the knee and is fairly common in children. Specific knee means syphilis of the knee and generally occurs in both knees.
The Tibia.—[The tibia or shin bone] is next longest to the femur and is on the inner side of the leg, corresponding to the ulna in the arm. The shaft is prismoid and is more slender for the lower quarter, where fracture is consequently most frequent. The anterior border forms the crest or shin and can be felt for its upper two-thirds. The lower extremity, which is smaller than the upper, articulates with the astragalus bone of the ankle and with the fibula. Its head or upper extremity is expanded into two lateral tuberositis for articulation with the femur and for muscular attachment, both of which can easily be felt just below the bend of the knee. Their upper surfaces are smooth and concave, with a vertical bifid spine in the middle and a prominent tubercle for the attachment of the semilunar cartilages on either side. On the anterior surface of the head, below, is a rough eminence or tubercle, which also can be felt. The lower part of this is for the attachment of the ligamentum patellæ, while the upper part, which is smoother, is for the bursa that is placed under the tendon to prevent friction. On the back of the outer tuberosity is a facet for the head of the fibula. At the lower end there projects downward on the inner side, overhanging the arch of the foot, the internal malleolus, the prominent part of the ankle. It is on a higher level and somewhat farther forward than the external malleolus.
The Fibula.—[The fibula] is the most slender of all the bones in proportion to its length and is on the outer side of the leg. Its head is small and placed toward the back of the tibia below the knee-joint, from which it is excluded. The head articulates with the external tuberosity and has extending upward from it the styloid process. To it is attached the biceps tendon or outer hamstring. At the lower extremity of the shaft is the external malleolus, which articulates with the astragalus and forms the outer ankle. The only parts of the fibula that can be felt, besides the malleolus, which is very prominent, are the head and the lower external surface of the shaft.
In fracture of the leg both bones are usually broken, though either may be broken separately. Pott’s fracture is fracture of the lower fibula, and may be caused by stamping hard when stepping on to the sidewalk. In rickets the tibia becomes bowed outward and forward, causing bow leg, a condition which in very young children may be rectified by manipulation. Later on braces are needed and after five years the bones have to be broken and set straight.
The Ankle.—The ankle or [tarsus] has but seven bones where the wrist has eight. They are the os calcis or heel bone, which is the largest and strongest and forms the tuberosity of the heel; the astragalus, which is next largest and helps to form the ankle-joint; the [cuboid]; the [navicular] (boat-like) or scaphoid; and the internal, middle, and external [cuneiform bones]. The astragalus is above and partially in front of the os calcis, to which is attached the tendo Achillis. The [cuboid] is on the outer side of the foot, in front of the os calcis and behind the metatarsals. It is noticeable in congenital club-foot, in which condition the tarsal bones may be distorted in shape and misplaced. The navicular or scaphoid is on the inner side of the foot, between the astragalus and the three cuneiform bones.
The Foot.—There are five [metatarsal bones] in the foot, corresponding to the five metacarpals in the hand, and the toes have the same number of [phalanges] as the fingers, though they are shorter and stronger. The big toe corresponds to the thumb.
Fig. 80.—Bones of the right foot, dorsal surface: 1, Astragalus; 2, talus; 3, os calcis, 4, navicular; 5, internal cuneiform; 6, middle cuneiform; 7, external cuneiform; 8, cuboid; 9, metatarsus; 10-14, phalanges. (Leidy.)
Fracture of the os calcis and the astragalus are most commonly caused by a fall from a height, while the metatarsals and phalanges are generally broken by something heavy falling upon them. Because of their delicate structure, their distance from the heart, and the differences of temperature to which they are subjected, the tarsal bones are especially liable to become tubercular, amputation of the feet even becoming necessary at times. In diabetes there may be a perforating ulcer on the sole of the foot and the bone may become diseased.
