What does diaphysis mean?
The diaphysis is the long, tubular shaft that forms the middle section of a long bone such as the femur, tibia, or humerus. Built largely of dense compact bone, it surrounds a hollow medullary cavity containing yellow marrow and is capped at both ends by the epiphyses — the widened extremities that form joints. In children and adolescents, the diaphysis is separated from each epiphysis by a cartilaginous growth plate, which is why injuries near these junctions are treated with particular care. In everyday language the word never appears; it belongs firmly to anatomy lectures, orthopaedic clinics, and radiology reports, where phrases like 'mid-diaphyseal fracture' pinpoint breaks located along the shaft rather than at either end of the bone. Its Greek roots mean literally 'a growing through,' reflecting how anatomists once understood bone development. For anyone reading a fracture report or studying skeletal structure, it is the precise term for a bone's working middle.
nounThe shaft or central tubular portion of a long bone, lying between the two ends (epiphyses). It consists mainly of compact bone surrounding the marrow cavity.
- The elongated shaft of a long bone, between the epiphyses, composed chiefly of compact bone enclosing the medullary cavity.
"The fracture ran cleanly across the midshaft of the femur, entirely within the diaphysis."
"Growth in the length of the bone occurs at the growth plates where the diaphysis meets each epiphysis."
"The X-ray revealed an undisplaced spiral fracture of the humeral diaphysis."
Follows the Greek-style plural in '-es', pronounced /daɪˈæfɪsiːz/.
"Both femoral diaphyses appeared intact on the follow-up scan."
Every long bone in your body has exactly one — and when doctors say a 'diaphyseal fracture,' they mean the break is dead centre down the bone's main shaft.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of diaphysis
Diaphysis comes from the Greek 'diaphysis,' meaning 'a growing through,' formed from 'dia-' ('through') and 'phyein' ('to grow'). It entered English as a term of anatomy, alongside sibling coinages built on the same root such as 'epiphysis' and 'apophysis,' which name other parts of the bone. The related Greek root also gave English words like 'physics,' originally the study of natural things and their growth.
Related word forms
How diaphysis is actually used
A technical term confined to anatomy, orthopaedics, and radiology; it is rarely used outside medical contexts. The standard plural is 'diaphyses.' The adjective 'diaphyseal' (also spelled 'diaphysial') is more frequently encountered in clinical writing than the noun itself, e.g. 'diaphyseal fractures.'
Easily confused with diaphysis
The epiphysis is the rounded end of a long bone, whereas the diaphysis is its long central shaft.