Radiography

The clinical examination should determine which radiographs are necessary to support the diagnosis. Standard views of the wrist include posteroanterior, lateral, and oblique views. Although these views are sufficient in the majority of cases, other projections may be necessary to profile specific carpal injuries.

The key to interpreting the radiograph is to first assure proper positioning, then identify specific features on each projection. On a properly positioned posteroanterior view, the distal radius and ulna should not overlap at their distal articulation and the axis of the third metacarpal should parallel that of the radius. Besides looking for disruption of the bony cortex, key elements on the PA view are illustrated on Fig.:...i262-i1.

On the PA view, three smooth arcs outline the articular surfaces at the radiocarpal and midcarpal joints. Two of these arcs are formed by the proximal and distal articular surfaces of the scaphoid, lunate, and triquetrum. The third arc is formed by the proximal articular surface of the capitate and hamate in the midcarpal joint. Any distortion of these lines implies a possible fracture, dislocation, or subluxation at the site.

The carpal bones fit together like a jigsaw puzzle, the pieces are separated by a narrow 1 to 2 mm joint space. This space is increased or obliterated with ligament disruption, carpal instability patterns, or fractures/dislocations. This occurs most often around the lunate at the scapholunate and capitolunate joints. Unfortunately, incorrect positioning can produce overlap patterns that could be misinterpreted as pathological. For example, radial deviation of the wrist causes normal physiological palmar rotation of the proximal carpal row. The dorsal rim of the lunate will overlap the capitate and obliterate the capitolunate joint space. The scaphoid that should appear elongated on the PA view appears shorter as it rotates palmar and can be confused with a rotatory subluxation of the scaphoid.

The radial styloid should project 8 to 18 mm beyond the distal radioulnar joint and create an ulnar inclination to the distal radius of 15 to 25 degrees on the PA view. Distal radius fractures can alter these measurements. At the distal radioulnar joint, the ulna and adjacent portion of the radius should be of equal length, and the distal radius should articulate with at least half the lunate. The extrinsic ligaments, along with the triangular fibrocartilage complex, prevent ulnar translocation (the migration of the carpals down the ulnar tilt of the radiocarpal surface). The lunate would have less contact and support from the radius if ulnar migration were present. A shorter ulna (negative ulnar variance) also provides less support to the lunate and increases the potential shear stress to the lunate. Although negative ulnar variance is a normal variant, its presence predisposes the lunate to injury.

The lateral radiograph is important for determining carpal alignment and degree of fracture angulation. The first step, again, is assuring that the wrist is properly positioned on the radiograph. The radius and ulna should completely overlap one another, and the radial styloid should be centered over the distal radial articular surface. The key features on this view are illustrated on Fig 262-2.

FIG. 262-2. Key elements on a normal lateral view. (1) three Cs sign; (2) capitolunate angle is <10 to 20 degrees; (3) scapholunate angle is <60 degrees; (4) radial volar tilt of 10 to 15 degrees. (With permission from Chin HW: Injuries of the wrist, in Hart RG, Rittenberry JJ, Uehara DT (eds): Handbook of Orthopaedic Emergencies. Philadelphia, Lippincott-Raven, 1998.)

The axis of the radius, lunate, and capitate is colinear on the lateral view. If the articular surfaces of these bones were highlighted, they would appear as three consecutive Cs in a row. This provides a simple radiographic assessment of wrist dislocation. Measurement of the capitolunate and scapholunate angles is a more precise assessment of carpal alignment. The axis of the capitate, lunate, and scaphoid runs through the center of their proximal and distal articular surfaces. The axis of the lunate and capitate should nearly overlap and form an angle that is less than 10 to 20 degrees. The scaphoid is normally palmar flexed on the lateral view; its axis should form an angle that is between 30 to 60 degrees with the lunate. Deviation from either of these angles suggests ligament disruption and carpal instability patterns Fig 262-3.

FIG. 262-3. A. Normal wrist. Axis of the radius (R), lunate (L), and capitate (C) are colinear. The capitolunate angle (CL) is less than 20 degrees and the scapholunate angle (SL) is between 30 and 60 degrees. B. Dorsal intercalated segment instability (DISI). The lunate tilts dorsal and slides palmar, increasing the capitolunate angle. The scaphoid tilts more palmar and increases the scapholunate angle. The axes of the radius, lunate, and capitate take on a zigzag pattern (dark line). C. Volar intercalated segment instability (VISI). The lunate tilts palmar and the capitolunate increases, but the scapholunate angle is maintained. The zigzag pattern is in the opposite direction.

Fractures of the distal radius are the most common fracture in the wrist. While a displaced fracture is the obvious deformity, the alteration of the normal volar tilt of 10 to 15 degrees of the distal articular radial surface has greater long-term consequences. The shape of the distal radius, distal ulna, and triangular fibrocartilage has a significant influence on carpal alignment and movement.

Other radiographic views profile specific areas of the wrist. Oblique views are performed in either partial pronation or supination. They project the scaphotrapezium joint or pisiform away from the overlapping adjacent carpal bones. The scaphoid view is a coned-down PA view of the scaphoid in ulnar deviation. This position extends the normal flexed posture of the scaphoid so that the bone is profiled lengthwise. This may assist in detecting subtle fractures. The carpal tunnel view is a tangential view through the carpal tunnel and is helpful in visualizing the pisiform and hook of the hamate. Motion studies are dynamic views in flexion, extension, and radial and ulnar deviation. They examine relative carpal movement to one another and stress the intercarpal ligaments for laxity characterized by widening of the intercarpal space. Likewise, the grip compression or fist view is a stress view in the PA projection of a tightly clenched fist. The capitate is pushed into the proximal carpal row and forces the carpal bones apart if the intrinsic intercarpal ligaments are torn.

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