Diaphysis
Also known as: shaft of long bone
The tubular shaft of a long bone: a thick wall of compact bone surrounding the medullary cavity. It forms from the primary ossification centre.
Overview
The diaphysis is a hollow cylinder — a shape that gives maximal resistance to bending and torsion for a given mass. Its wall is thick compact bone, thickest at mid-shaft, covered by periosteum and lined by endosteum; its interior is the medullary cavity, filled in adults with yellow (fatty) marrow. One or two nutrient foramina transmit the nutrient artery obliquely through the cortex, directed away from the more actively growing end ("to the elbow I go, from the knee I flee").
The diaphysis is the first part of a long bone to ossify: a periosteal bone collar forms around the mid-shaft of the cartilage model and the primary ossification centre develops inside it during weeks 7–12 of fetal life.
- Location
Middle portion of a long bone, between the two metaphyses.
Parts & subdivisions
- Thick compact bone built of osteons.
- Central cavity containing yellow marrow in adults.
- Nutrient foramen and canalOblique channel for the nutrient artery and vein, directed away from the growing end.
Anatomy
- Arterial supply
Nutrient artery (inner two-thirds of cortex and marrow) and periosteal arteries (outer third).
- Ossification
Primary ossification centre, fetal weeks 7–12 in most long bones (clavicle earlier, week 5–6).
Function
- Transmits load between the ends of the bone
- Acts as a lever for muscles attached along its length
- Houses yellow marrow (fat storage)
Clinical significance
Shaft fractures
Diaphyseal fractures of the femur may lose 1–1.5 L of blood into the thigh; tibial shaft fractures are often open because the anteromedial surface is subcutaneous, and are a classic cause of compartment syndrome.
Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.