Changes in the Appendicular Skeleton with Age

The appendicular skeleton develops as limb buds during embryogenesis and consists of hyaline cartilage and fibrous membranes.

As the embryo grows, most of the appendicular skeleton develops by endochondral ossification, in which bones form by replacing cartilage.

Only the clavicles develop by intramembranous ossification, in which the bone forms directly from the embryonic connective tissue or mesenchyme.

After birth, the lower limbs grow rapidly, becoming proportionate to the trunk's size by age ten, and continue to grow to reach the adult length.

Other parts, such as the female pelvis, broaden during puberty in preparation for childbearing and continue to enlarge until age twenty-five.

After twenty-five, equal rates of bone resorption and deposition result in very few changes in a healthy skeleton until middle age.

With advancing age, the bone resorption rate exceeds the bone deposition rate. Thus, bones become more porous, which increases the risk of fracture, especially in the neck of the femur.