What does capitellum mean?
The capitellum is a small, rounded, dome-like prominence located on the outer (lateral) side of the lower end of the humerus, the upper arm bone. Its name comes from the Latin diminutive meaning 'little head,' reflecting its ball-like shape. The term belongs chiefly to the vocabulary of anatomy, orthopaedic surgery, and radiology, where precision about joint surfaces matters. Functionally, the capitellum forms half of a crucial joint: it fits against the cupped head of the radius, one of the two forearm bones, allowing the forearm to rotate so the palm can turn up or down — the motion used when turning a key or receiving change. Because this rounded surface carries substantial load, particularly in athletes who throw or bear weight on their arms, injuries such as osteochondral lesions and fractures of the capitellum are well-recognised clinical entities. In broader comparative anatomy, similar small head-like bony knobs may also be described as capitella.
nounA small rounded, head-like protuberance on a bone, especially the knob at the lower end of the humerus that articulates with the radius in the forearm.
- Anatomy: the rounded, hemispherical eminence on the lateral side of the lower end of the humerus that articulates with the head of the radius.
- General anatomy/osteology: any small head-like or knob-like prominence on a bone.
"The surgeon noted a small fracture of the radial head where it meets the capitellum of the humerus."
"MRI revealed an osteochondral lesion of the capitellum in the young gymnast's dominant elbow."
"The capitellum, though small, bears a remarkable share of load during throwing motions."
The Latin-derived plural is standard in medical and comparative-anatomy writing; the singular predominates in everyday clinical usage since each human has one capitellum per arm.
"In many mammals, the corresponding capitella show species-specific variation in size and curvature."
Your elbow owes its smooth rotation to a Latin word for 'little head' — the capitellum is literally the tiny ball your radius spins on every time you turn a doorknob.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of capitellum
The word derives from New Latin 'capitellum,' a diminutive of Latin 'caput' ('head'), literally meaning 'little head.' It entered anatomical nomenclature alongside other Latinate terms adopted during the standardisation of medical terminology, and it remains a fixed part of international anatomical vocabulary. It shares its root with words built on 'caput,' including 'capital,' 'capitulate,' and 'decapitate.'
How capitellum is actually used
A technical term used almost exclusively in anatomy, orthopaedics, radiology, and veterinary medicine; it would sound out of place in general conversation. Pluralization follows Latin conventions (capitella), which is common in medical writing, though singular use dominates in clinical contexts.
Easily confused with capitellum
The trochlea is the pulley-shaped medial part of the humerus's lower end that articulates with the ulna, while the capitellum is the adjacent rounded knob that articulates with the radius.