The wrist is the area from the distal radius and ulna to the carpometacarpal
joints. It is a complex unit with articulations among the eight
carpal bones and the distal radius and ulna. Wrist injuries are
common, accounting for 2.5% of ED visits annually.1 Clinical
diagnosis is often difficult, and even subtle injuries may lead
to significant impairment if not properly diagnosed and treated.
Management options vary from conservative to surgical, so an understanding
of the functional anatomy, mechanisms of injury, and clinical evaluation
is needed for proper diagnosis and treatment.
The distal radius is the only forearm bone that articulates directly
with the carpal bones (scaphoid and lunate). The distal radius has
three articular surfaces: radiocarpal, distal radioulnar, and the
triangular fibrocartilage complex. The radiocarpal surface is concave
and tilted in two planes. It has an ulnar inclination, or tilt,
of 15 to 25 degrees in the frontal plane, and a volar tilt of 10
to 15 degrees in the sagittal plane2 (Figure 266-1).
The ulna is separated from the carpal bones by the triangular fibrocartilage
complex, the main stabilizer of the distal radioulnar joint, on
its distal end. The triangular fibrocartilage complex forms a smooth, continuous,
ulnarly directed extension of the distal radial surface, and supports
the lunate and triquetrum on the distal ulna. The distal radius has
a concave sigmoid notch at its ulnar aspect that articulates with
the curvature of the ulnar head, which permits wrist rotation during
pronation/supination of the forearm.3 The
distal radioulnar joint is also supported by dorsal and volar radioulnar
ligaments that merge with the triangular fibrocartilage complex.4
Key elements on a normal posteroanterior view. 1. The carpal
bones are arranged in two rows forming three smooth arcs (Gilula lines).
2. The carpal bones are separated by a uniform 1- to 2-mm space. 3.
The scaphoid (S) is elongated. 4. The radius has
an ulnar inclination of 13 to 30 degrees. 5. The radial styloid
projects 8 to 18 mm. 6. Half the lunate articulates with the radius,
with equal length over the ulna (neutral ulnar variance). C = capitate;
H = hamate; L = lunate; P = pisiform;
Tm = trapezium; Tq = triquetrum; Tz = trapezoid.
Eight carpal bones are arranged in two rows. The distal carpal
row (trapezium, trapezoid, capitate, and hamate) is joined tightly
together and to the adjoining metacarpals. This row is quite stable,
and moves with the metacarpals as a unit in a relatively stable
arch. The proximal carpal row (scaphoid, lunate, triquetrum, and pisiform)
is also arranged in an arch between the distal radius and the distal
carpal row. In this arrangement, the proximal row functions as a
mobile link, or “intercalated segment,” and is
potentially unstable by virtue of this position. The scaphoid is
critical to wrist stability, by ...