Derivation and Terminology

Humerus is derived from the Latin humer, meaning “shoulder” (3). The plural of humerus is humeri.

Ossification Centers

The humerus has eight ossification centers: one each for the

body, the head, the greater tuberosity, the lesser tuberosity,

the capitulum, and the trochlea, and one for each epicondyle (Fig. 1.10). The ossification center for the body

appears near the central portion of the bone at approximately the eighth week of fetal life. Ossification soon

extends to either end of the bone, so that at birth the

humerus is nearly completely ossified, with only the ends

remaining cartilaginous.

In the proximal end of the humerus, ossification begins

in the head of the bone during the first year (or earlier in

some individuals). The center for the greater tuberosity

begins to ossify during the third year, and the center for the

lesser tuberosity begins to ossify during the fifth year. The

centers for the head and tuberosities usually join by the

sixth year, forming a single large epiphysis that fuses with

the body in approximately the twentieth year (see Fig.

1.10B).

In the distal end of the humerus, ossification begins in

the capitulum near the end of the second year and extends

medially to form the major part of the articular end of the

bone. The center for the medial part of the trochlea appears

at approximately 10 years of age. The medial epicondyle

begins to ossify at approximately the fifth year, and the lateral epicondyle at approximately the twelfth or thirteenth

year. The lateral epicondyle and both portions of the articulating surface (having already joined together) unite with

the body. At approximately the eighteenth year, the medial

epicondyle is joined to the body of the humerus.

Osteology of the Humerus

The humerus is the largest bone in the upper extremity.

Each end of the humerus is composed of cancellous bone

covered by thin cortical bone. The diaphysis consists of

thick cortical bone throughout its length, with a well

defined medullary canal. The medullary canal extends the

entire length of the humerus. At the proximal and distal

metaphyses, the medullary canal changes to cancellous

bone, and the outer cortex becomes thinner (Figs 1.11 to

1.13).