[Morphological transformation of limb bones with growth].

The development of the long limb bones consists of two developmental types, one for the length and the other for the thickness. Although the development of the length is due to the growth of the epiphyseal cartilage, the development of width is due to the addition of bone to the periosteal membranes. Growth of bones is influenced not only by chemical factor, such as hormone or vitamin, but also by physical factor such as electrical or mechanical stresses. Changes in the development of the limb bones caused by mechanical stress were studied. The limb bones, which belonged to a hydrocephalic patient who had been bedridden for 16 years, were measured. The lower limb bones had almost no mechanical stress such as weight or walking, due to his being bedridden for many years. He also could not exercise his upper extremity, hence mechanical stress to the upper limb bones was minimal. The circumference at the mid-shaft of each long bone was shorter than the average circumference of the same age. The thickness was also narrower, suggesting Wolff's law. However, no difference was found in length between the subject and the average. While mechanical stress was a factor that accelerated the thickness of the limb bones, stress did not have much influences on the length of the long limb bones. The length of the right clavicle was longer than that of the left due to the pressure of maintaining the same posture. In an experimental study of tail suspended rats showed that there was no significant difference in the length of hindlimb between the experimental group and control group, though a difference was found in the length of forelimb. The length of forelimb in the experimental group was significantly shorter than the control group due to weight pressure. This result suggests that physical pressure in the longitudinal direction is one of the factors that inhibits the growth of the length of bones and that mechanical stress is important for the morphology and the function of bones. Stress exerts different influence to accelerate or inhibit bones according to the direction.