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Anatomy and
Principles of Evaluation
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Articulations of the distal humerus and proximal ulna and radius form the elbow joint
(Figure 267-1).
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The epicondyles are nonarticulating surfaces
that serve as sites of origin for forearm, wrist, and digit flexors,
and pronators (medial), and extensors and supinators (lateral).
Medially, the trochlea articulates with the olecranon to form a
uniaxial hinge joint. Laterally, the capitellum abuts the radial
head to form a pivot joint. Between the condyles, the coronoid fossa
is anterior, and the olecranon fossa is posterior. These allow for
full flexion and extension of the ulna. The radial fossa lies proximal
to the capitellum anteriorly and permits full flexion of the radius.
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Several important neurovascular structures lie in close proximity
to the distal humerus, and evaluation of their function is essential.
These include the brachial artery, palpable just medial to the distal
biceps tendon in the antecubital fossa, and the radial, median,
and ulnar nerves. The ulnar nerve is palpable as a cord just posterior
to the medial epicondyle, and is vulnerable to injury with trauma
over this area.
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The neuroanatomy is best understood by appreciating the neural
control of basic wrist and finger movement (Figure
267-2). The radial nerve travels over the lateral epicondyle
and supplies the muscles of wrist extension before it branches off
into the posterior interosseous nerve. This branch travels around
the proximal radius and controls the muscles of finger and thumb
extension. The remainder of the radial nerve is purely sensory and innervates
the dorsal aspect of the hand from the thumb to the radial half of
the ring finger. Thus, the proximal portion of the radial nerve
controls the more proximal function of wrist extension, the distal
branch (posterior interosseus nerve) controls the more distal function
of finger extension, and another branch is purely sensory. Therefore,
an isolated injury to the posterior interosseous branch affects
finger extension but spares wrist extension and sensation to the
dorsum of the hand. The single best test of radial nerve
motor function is to have the patient extend both the wrist and
fingers against resistance (Table 267-1). Sensation
is tested over the dorsum of the thumb index web space.
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