Biomedical Engineering Reference
In-Depth Information
fractures and in the verification of their correct reduction. On
its medial side, the distal end of the radius has an ulnar notch,
for articulation with the head of the ulna. At about the middle of
the convex dorsal aspect of the distal end of the radius, a small
prominence, the dorsal tubercle, may be felt. The inferior sur-
face of the distal end articulates with the lunate (medial) and the
scaphoid (lateral). A fall on the outstretched hand may result in
a fracture of the distal end of the radius, in which the distal frag-
ment is displaced posteriorly and generally becomes impacted,
bringing the styloid processes of the radius and ulna to approxi-
mately the same horizontal level.
• The ulna (2) forms the medial support of the forearm. It is longer
than and medial to the radius. It articulates with the humerus
proximally, the radius laterally, and the articular disc distally.
The proximal end includes the olecranon and the coronoid pro-
cess. The olecranon is the prominence of the posterior elbow that
rests on a table when a person leans on the elbow. The lateral epi-
condyle, the tip of the olecranon, and the medial epicondyle are
in a straight line when the forearm is extended, but form an equi-
lateral triangle when the forearm is flexed. The superior aspect of
the olecranon receives the insertion of the triceps. The posterior
aspect, covered by a bursa, is subcutaneous. The anterior part of
the olecranon forms a part of the trochlear notch, which articu-
lates with the trochlea of the humerus. The coronoid process,
which completes the trochlear notch, projects anteriorward and
engages the coronoid fossa of the humerus during flexion. It is
prolonged inferiorward as a rough area termed the tuberosity of
the ulna. The radial notch is on the lateral aspect of the coronoid
process and articulates with the head of the radius.
• The carpal bones (16) are eight pairs of bones of the wrist and
consist of (a) four proximal bones (scaphoid, lunate, triangular
or triquetral, and pisiform), and (b) four distal bones (trapezium,
trapezoid, capitate, and hamate). The posterior aspect of the
intact carpus is convex and the anterior aspect is concave, where
it is bridged by the flexor retinaculum to form the carpal canal
or tunnel for the flexor tendons and the median nerve. Hence,
the posterior surfaces of the carpals are generally larger than the
anterior, with the exception of the lunate, where the converse
holds. The flexor retinaculum extends between the scaphoid and
trapezium laterally and the triquetrum and hamate medially.
These four bones can be distinguished by deep palpation. The
scaphoid has a tubercle on its anterior side that can be felt under
cover of and lateral to the tendon of the flexor carpi radialis. A fall
on the outstretched hand may result in fracture of the scaphoid,
