b. The radius is located on the lateral side of the forearm parallel to the ulna.
The proximal end is small and has a head, neck, and tuberosity. The shallow cup, or
fovea, on the proximal surface of the head articulates with the capitulum of the
humerus. On the broad medial surface, the head articulates with the radial notch of the
ulna. Below the neck on the medial side is the radial tuberosity (or tubercle). The distal
end is large and club-shaped and forms the largest part of the wrist joint. It has two
articular surfaces, one broad area that articulates with two carpal bones (the navicular
and lunate) and a smaller surface on the medial side, the ulnar notch, that articulates
with the ulna. Distally, the lateral surface extends into the styloid process. Colles
fracture occurs at the distal radius with posterior displacement of the distal fragments, a
"silver fork deformity."
The bone of the arm is the humerus (figures 2-4 and 2-5). It is the longest and
largest bone of the upper limb.
a. Its proximal extremity has a hemispherical head. The anatomical neck
separates the head from two large bony prominences. The greater tubercle, situated on
the lateral aspect, and the lesser tubercle, situated on the anterior surface. Between
the two tubercles is the bicipital, or intertubercular groove. The surgical neck below the
tuberosity is frequently the site of fractures.
b. Proximally, the shaft is almost cylindrical, but it becomes flat distally.
Approximately in the middle lateral third of the shaft is the deltoid tuberosity.
c. The broad distal extremity consists laterally of the capitulum and medially of
the trochlea. The capitulum articulates with the fovea on the head of the radius and the
trochlea with the trochlear notch on the ulna. Proximal to these two eminences on the
anterior aspect are the radial and the coronoid fossa (which receive the head of the
radius) and the coronoid process of the ulna, respectively, when the forearm is flexed.
Posterior to the trochlea is the olecranon fossa, which receives the olecranon process of
the ulna when the forearm is extended. On the sides of the distal end are two
prominences, the lateral and medial epicondyles.