Boyer diss 2009 1046..

tuberosity. This crest probably delimits the radial edge of the compartment for the digital
extensor musculature. The ulnar margin of the shaft of the radus develops a distinct crest
for the interosseous membrance toward its distal end. The shaft swells abruptly to
accommodate the distal articular surface. The dorsoradial margin of the distal epiphysis
is marked by three tuberosities that formed the bony boundaries of the three extensor
tendon compartments that cross the proximal carpal joint. From radial to ulnar these
tuberosities correspond to the styloid process, Lister’s tubercle, and a frequently present
but unnamed tubercle (Stern, 1988). The first extensor compartment would have been
located radial and ventral to the styloid process. The distal articular surface itself is
triangular in distal view. The radial margin forms a vertex of the triangle, while the ulnar
surface is the opposing base of the triangle. The distal articular surface is marked by a
faint dorsoventral ridge reflecting the respective positions of the scaphoid and lunate on
either side of it. Ulnar to the lunate area, the articular surface extends on to the radial
shaft for contact with the ulna.
Function.—The spherical depression of the central fossa of the radial head
suggests that the radius was axially mobile, as does the corresponding morphology of the
humeral capitulum. A distally positioned, dorsally elevated pronator teres muscle
attachment would provide a large area and lever arm for this muscle to resist substrate
reaction forces causing supination, whereas the supinator muscle, attaching along the
ulnar margin of the pronator teres attachment, could resist the opposite motion. Together,
these muscles, as well as biceps brachii and some of the muscles originating from the
supinator crest, could stabilize or rotate the humeroradial joint. The shallow distal
articular surface suggests a mobile radiocarpal joint. The orientation of the joint surface
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