BONY ANATOMY AND
LANDMARKS
Anteriorly, the contour of the biceps muscle is
seen starting in the upper arm and extending distally into the cubital
fossa, which is the inverted triangular depression on the anterior aspect
of the elbow. The flexion crease along the anterior elbow is in line with the
medial and lateral epicondyles and is 1 to 2 cm proximal to the joint line when
the elbow is extended. The superficial cephalic and basilic veins are the most
prominent super-ficial major contributions of the anterior venous system and
communicate by way of the median cephalic and median basilic veins to form a
pattern resembling an M over the cubital fossa. Laterally, the tip of the
olecranon, the lateral epicondyle, and the radial head form a palpable triangle
called the posterolateral soft spot that can show evidence of an
effusion from the elbow joint and serves as an important landmark for joint
aspiration and for elbow arthroscopy. The proximal extensor forearm
musculature originates from the lateral epicondyle and forms the lateral
margin of the cubital fossa and the lateral contour of the forearm and
comprises the brachioradialis and the extensor carpi radialis longus and brevis
muscles. The proximal flexor pronator musculature forms the contour of
the medial anterior forearm extending from the medial epicondyle and includes
the pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi
ulnaris. The relationship of these muscles can be approximated by placing the
opposing thumb and the index, long, and ring fingers over the anterior medial
forearm. Posteriorly, the contour of the triceps muscle is seen in the upper
arm extending to the tip of the olecranon. More distally, the proximal forearm
is contoured dorsally by the lateral extensor musculature, consisting of the
anconeus, extensor carpi ulnaris, extensor digitorum quinti, and extensor
digitorum communis.
The main bone of the upper arm is the humerus.
It is a long bone composed of a shaft and two articular extremities. The
proximal humerus, which includes the humeral head, greater and lesser
tuberosity, and surgical neck, is discussed in detail in Section I, Shoulder.
The body, or shaft, of the humerus
begins just below the surgical neck. It is somewhat rounded above and prismatic
in its lower portion. Above and medially, the coracobrachialis muscle is
received near the middle of the shaft; about opposite laterally is the
prominent deltoid tuberosity. This is continued upward in a V-shaped
roughening for the insertion of the deltoid muscle. Just below the deltoid
tuberosity, a groove for the radial nerve indents the bone posteriorly,
spiraling lateralward as it descends. Sharp lateral and medial supracondylar
ridges spring from the respective borders inferiorly and continue into the
lateral and medial epicondyles of the humerus. The inferior extremity of the
bone is flattened anteroposteriorly and mediolaterally, and it is widened by
the medial and lateral epicondyles. The lateral epicondyle is not conspicuous,
but the medial epicondyle forms a marked medial projection above the elbow.
Projecting somewhat backward, it is grooved behind for the ulnar nerve.
The articular surfaces for the
radius, ulna, capitellum, and trochlea are directed somewhat forward;
consequently, the inferior extremity of the humerus appears to curve
anteriorly. The capitellum is roughly globular. Smaller than the
trochlea, it articulates with the cupped upper surface of the radius. Above it
is a shallow fossa, the radial fossa, for the reception of the edge of
that bone during full flexion of the elbow. The trochlea is shaped like
a spool, with a deep depression between two well-marked margins. The depression
is slightly spiral and receives the central ridge of the trochlear notch of the
ulna. The medial rim of the trochlea is the more prominent; the lateral rim is
only a small elevation separating the trochlea from the capitellum. Above the
trochlea is the coronoid fossa for the reception of the coronoid process
of the ulna in front and the olecranon fossa for the olecranon behind.
The humerus ossifies from eight
centers of ossification: one for the shaft and seven for the processes-head,
greater and lesser tuberosities, trochlea, capitellum, lateral epicondyle, and
medial epicondyle.
The shaft appears near the middle of
the bone in the eighth week of fetal life and then extends toward its
extremities. At birth, the humerus is ossified in nearly its whole length; only
its extremities remain cartilaginous. Shortly after birth, ossification begins
in the head of the bone, followed by the appearance of the centers in the
greater and lesser tuberosities at 3 to 5 years of age, respectively. By age 6,
all these centers have merged into one large epiphysis. In the distal humerus,
secondary centers appear for the capitellum at age 2, for the trochlea at age 9
or 10, and in the lateral epicondyle at ages 13 to 14. These centers unite and
fuse with the shaft at about age 13 in females and age 15 in males. The
separate center for the medial epicondyle appears a ages 6 to 8 and fuses with
the shaft at ages 14 to 16.
