Summary of general anatomy of short bone: lecture notes

 

Summary of general anatomy of  short bone

Short Bones

Short bones are designated as those bones that are as wide as they are long. Their primary function is to provide support and stability with little to no movement. They are one of five types of bones: short, long, flat, irregular and sesamoid.

Short bones are shaped roughly as a cube and contain mostly spongy bone. The outside surface is comprised of a thin layer of compact bone. Short bones are located in the hands and feet. The patella (kneecap) is also considered a short bone.

Where a part of the skeleton is intended for strength and compactness combined with limited movement, it is constructed of a 6 number of short bones, as in the carpus and tarsus.

 The patellæ, together with the other sesamoid bones, are by some regarded as short bones.

The carpal bones are ossified endochondrally (from within the cartilage) and the ossific centers appear only after birth.  The formation of these centers roughly follows a chronological spiral pattern starting in the capitate and hamate during the first year of life. The ulnar bones are then ossified before the radial bones, while the sesamoid pisiform arises in the tendon of the flexor carpi ulnaris after more than ten years. The commencement of ossification for each bone occurs over period like other bones. This is useful in forensic age estimation

Appearance of ossification centers of carpal bones

 

 

Bone	Average	Variation	Variation
Capitate	2.5 months	1–6 months	1–5 months
Hamate	4-5.5 months	1–7 months	1–12 months
Triquetrum	2 years	5 months to 3 years	9 months to 4 years and 2 months
Lunate	5 years	2-5.5 years	18 months to 4 years and 3 months
Trapezium	6 years	4–8 years
Trapezoid	6 years	4–8 years
Scaphoid	6 years	4–7 years
Pisiform	12 years	8–12 years

 

 

 

 

Ossification of tarsal bone

Primary ossification centers present at birth

Visible on x-ray from birth:

·         calcaneus: 6 months in utero

·         talus: 7 months in utero

·         cuboid: 9 months in utero

·         metatarsals: 9 weeks in utero

·         phalanges: 3-10 months (proximal to distal)

Primary ossification centers developing after birth

Become visible on x-ray from:

·         lateral cuneiform: 1^st year

·         medial cuneiform: 3^rd year

·         intermediate cuneiforms and navicular: 4^th year

Secondary ossification centers

At the age of 3 years, secondary ossification centers of the navicular, metatarsals and phalanges should all be present. The last secondary ossification center to develop is the calcaneus appearing at 5 years.