4 The cartilaginous characteristics allow for sonographic evaluation of the hip in infants. The femoral head begins to ossify from the center outward at 2 to 8 months of age ( Fig. The femoral head is cartilaginous at birth and the acetabulum is composed of cartilage and bone. The femoral head is contiguous with the neck, which is contiguous with the diaphysis or shaft of the femur. At the rim of the acetabulum sits a lip of cartilage called the acetabular labrum ( Fig. The proximal aspect of the femur, the femoral head, is rounded and sits in the acetabulum.
This creates an articulation point for the femur. The acetabulum is located at the lateral aspect of these bones and is joined by a growth plate, the triradiate cartilage. The hip bone or coxal bone is composed of the ilium, ischium, and pubis ( Fig. The bones of the hip joint are composed of the pelvic girdle and the femur. The joints of the body begin to develop during the sixth week, and during the seventh week of development, the upper and lower limbs will rotate on their longitudinal axes. Myoblasts differentiate to develop into the muscles of the long bones. Initially, the limbs arise as buds with the distal ends developing into paddle-like structures from which the bones continue to develop and fingers and toes arise. The ossification of the bones of the arms and legs begins at the end of the third week, which marks the end of the embryonic period, although the development of bones continues into adult life. The cephalic end of the body and, along with cells derived from the neural crest, contribute to the development of the face and head. From the mesoderm, mesenchymal cells arise that are concentrated in The initial development of the mesoderm occurs in the latter part of the third week postconception, which marks the beginning of bone formation. The bones, connective tissues, and muscles are derived from the mesoderm. There are three germ layers from which all body systems form: the ectoderm, the mesoderm, and the endoderm.