Page 182 - Clinical Anatomy

ECA3 7/18/06 6:45 PM Page 167

Surface anatomy and surface markings 167

down upon confidently at this site. It then runs up the anterior aspect of the
forearm to lie in a groove along the lateral border of the biceps and then,
after piercing the deep fascia, in the groove between pectoralis major and
the deltoid, where again it can readily be exposed for an emergency cut-
down. It finally penetrates the clavipectoral fascia to enter the axillary vein.
The basilic vein runs along the posteromedial aspect of the forearm,
passes on to the anterior aspect just below the elbow and pierces the deep
fascia at about the middle of the upper arm. At the edge of the posterior
axillary fold it is joined by the venae comitantes of the brachial artery to
form the axillary vein.
Linking the cephalic and basilic veins just distal to the front of the elbow
is the median cubital vein, usually the most prominent superficial vein in the
body and visible or palpable when all others are hidden in fat or collapsed
in shock.
It was this vein that was favoured for the operation of bleeding, or phle-
botomy, in former days; the underlying brachial artery was protected from
the barber-surgeon’s knife by the bicipital aponeurosis, a condensation of
deep fascia passing across from the biceps tendon, which was therefore
termed the ‘grâce à Dieu’ (praise be to God) fascia.
In more modern times one tries to avoid using this vein for injection of
intravenous barbiturates and other irritating drugs because of the slight
risk of entering the brachial artery and also because of the danger of pierc-
ing a superficially placed abnormal ulnar artery in occasional instances of
high brachial bifurcation.

Nerves

Anumber of nerves in the upper limb can be palpated, particularly in a thin
subject; these are the supraclavicular nerves, as they pass over the clavicle,
the cords of the brachial plexus against the humeral head (with the arm
abducted), the median nerve in the mid-upper arm, crossing over the
brachial artery, the ulnar nerve in the groove of the medial epicondyle and
the superficial radial nerve fibres as it passes over the tendon of extensor
pollicis longus at the wrist.
The median nerve lies first lateral then medial to the brachial artery,
crossing it at the mid-upper arm, usually superficially but occasionally
deeply. This close relationship is of historical interest: Nelson had his
median nerve accidentally incorporated in the ligature around the artery
when his arm was amputated above the elbow.
Useful surface markings of other, impalpable, nerves may be listed as
follows.
1◊◊The axillary nerve is related closely to the surgical neck of the humerus 2
in (5cm) below the acromion process.
2◊◊The radial nerve crosses the posterior aspect of the humeral shaft at its
mid-point.
3◊◊The posterior interosseous branch of the radial nerve is located by Henry’s
method as it winds round the radius. Place three fingers along the radius,
the uppermost lying just distal to the radial head; the 3rd finger then lies
over this nerve.