The Upper Extremity 425ing to the thumb. They are also often designated as
thumb, index finger, middle finger, ring finger, and
little finger. The phalanges are termed the proximal,
middle, and distal phalanges for fingers 2 through- The thumb is also termed the pollex, and like the
hallux, it contains only two phalanges, the proximal
and distal phalanges.
The hand is joined to the forearm at the wrist
or radiocarpal joint. More specifically, the inferior
concave surface of the radius and the adjacent tri-
angular fibrocartilaginous disc articulate with the
convex articular surface formed by the proximal row
of carpals (scaphoid, lunate, and triquetrum bones)
as shown in figure 7.47. Note that due to the presence
of the fibrocartilage disc, the ulna does not directly
participate in the wrist joint. However, this disc adds
important stability to the wrist by binding the radius
and ulna together distally (Magee, 1997). It also
helps distribute the load between the radius and
ulna. It has been estimated that the radius bears 60%
of the load and the ulna 40% with the disc in place,
in contrast to 95% for the radius and 5% for the ulna
with the disc removed. The shape of the articular
surfaces makes the wrist a biaxial condyloid joint.
Hence, movements include flexion-extension and a
specially designated form of abduction-adduction.
Flexion refers to the motion of bringing the palm
of the hand toward the front of the forearm, while
the reverse movement of bringing the palm away is
termed extension of the wrist as seen in figure 7.48.
Abduction of the wrist refers to bringing the hand
away from the midline such that the lateral surface
of the hand (thumb) comes closer to the lateral
FIGURE 7.46 Bones of the hand (right hand, anterior
or palmar view).
FIGURE 7.47 Radiocarpal and midcarpal joints (left hand, anterior or palmar view).Triangular
fi brocartilage disc