Human Anatomy Vol 1

(mdmrcog) #1

Deltoid muscle

Deltoid tuberosity

Radial nerve

Olecranon fossa

Fi1.2.17: Relation of axillary, radial and ulnar nerues to the back
of +u(nerus

surgical neck, the radial at the radi"al grooae, nnd the
ulnar behind the medial epicondyle (Fig.2.l7).

The humerus ossifies from one primary centre and
7 secondary centres. The primary centre appears in
the middle of the diaphysis during the 8th week of
development (Table 2.1).
The upper end ossifies from 3 secondary centres-
one for the head (first year), one for the greater
tubercle (second year), and one for the lesser tubercle
(fifth year). The 3 centres fuse together during the
sixth year to form one epiphysis, which fuses with
the shaft during,the 20th year. The epiphyseal line
encircles the bone at the level of the lowest margin
of the head. This is the growing end of the bone
(remember that the nutrient foramen is always
directed away from the growing end).
The lower end ossifies from 4 centres which form

(^2) epiphyses. The centres include one for the
capitulum and the lateral flange of the trochlea (first
year), one for the medial flange of the trochlea (9th
year), and one for the lateral epicondyle (12th year):
All three fuse during the 14th year to form one
epiphysis, which fuses with the shaft at about l-
years. The centre for the medial epicondyle appears
during 4-6 years, forms a separate epiphysis, and
fuses with the shaft during the 20th year.
The common sites of fracture of humerus are the
surgical neck, the shaft, and the supracondylar
Supracondylar fracture is common in young age. It
is produced by a fall on the outstretched hand.
The lower fragment is mostly displaced
backwards, so that the elbow is unduly prominent,
as in dislocation of the elbow joint. This fracture
may cause injury to the median nerve. It may also
lead to Vollsnann's isclmemic contracture caused by
occlusion of the brachial artery (Fig. 2.18).
The three bony points of the normal elbow form
the equilateral triangle in a flexed elbow and are
in one line in an extended elbow (Fig. 2.19).
The humerus has a poor blood supply at the
junction of its upper and middle thirds. Fractures
at this site show delayed union or nonunion.
The head of the humerus commonly dislocates
inferiorly (Fig. 2.20).
The radius is the lateral bone of the forearm, and is
homologous with the tibia of the lower limb. It has an
upper end, a lower end and a shaft.
Side Delerminolion
1 Upper end is having disc shaped head while lower
end is expanded with a styloid process.
2 At the lower end, the anterior surface is in the form
of thick prominent ridge. \Mhile the posterior surface
presents four grooves for the extensor tendons.
3 The sharpest border of the shaft is the medial border.
Close to neck it presents a radial tuberosity.
(^4) Lower end presents a tubercle on the posterior
surface called as dorsal tubercle of Lister.
1 The head rs disc-shaped and is covered with hyaline
cartilage (Frg. 2.21).It has a superior concave surface
which articulates with the capitulum of the humerus
at the elbow joint. The circumference of the head is
also articular. It fits into a socket formed by the radial
notch of the ulna and the annular ligament, thus
forming the superior radioul-nar joint.
2 The neckis enclosed by the narrow lower margin of
the annular ligament. The head and neck are free
from capsular attachment and can rotate freely
within the socket.
3 The tuberosity lies just below the medial part of the
neck. It has a rough posterior part and a smooth
anterior part.

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