Critical Equipment

Critical equipment involved in the surgical technique is as follows.

Imaging

The injured wrist is imaged with a mini–fluoroscope to identify fracture displacement and ligament injury. Imaging is used to identify the fracture plane and position. This may impact the location and size of implant. Imaging may also identify other carpal or radius fractures not appreciated using standard radiographs, which require treatment. Excessive gapping between the carpal bones may suggest ligament injuries and will direct arthroscopic inspection.

Scaphoid imaging includes locating the central scaphoid axis. This is accomplished by pronating the wrist until the scaphoid poles are aligned, and flexing the wrist approximately 45 degrees until the cylinder of the scaphoid becomes a circle (Figure 16.1). A perpendicular placed at the center of the circle represents the central axis of the scaphoid. This perpendicular is the longest distance a straight line can be placed through the scaphoid, the central scaphoid axis. Along the central axis, the longest screw can be placed without violating the scaphoid cartilage envelope. Biomechanically, the longest screw distributes and reduces the bending forces—which act to displace the scaphoid. Finally, clinical reports confirm that screws placed along the central axes achieve faster healing than those placed eccentrically.¹²

FIGURE 16.1 Images demonstrating the position of the hand and central axis of the scaphoid.

Scaphoid displacement can occur either as lateral displacement visualized on a posterior–anterior view as a step–off (Figure 16.2) or as forward flexion of the distal fragment on the proximal fragment displaying a V separation of the dorsal cortex on lateral or oblique views (Figure 16.3)—a future humpback deformity. On the PA view, this displacement appears as a foreshortened scaphoid. At the completion of this survey, two decisions must be made. First, is the scaphoid grossly aligned or not? Second, are there other injuries that need to be addressed?

FIGURE 16.2 Translational displacement of the scaphoid.

FIGURE 16.3 Flexion deformity of an acute scaphoid fracture.

Grossly Aligned Scaphoid

With minimal (<1 mm) or no displacement on imaging, the next step is to place a guide wire down the central scaphoid axis. For a variety of reasons, it might be difficult to visualize the central axis. A simple technique we now use is an “external cross K–wire scaphoid guide,” which permits external sighting of the distal scaphoid by percutaneously placed perpendicular K–wires. It does not require continuous imaging to drive the wire along the central axis. Imaging is only used to set up the targeting system. This guide requires the placement of two K–wires in the distal scaphoid in the same axial plane, perpendicular to the scaphoid and offset in a 90–degree arc. One wire is driven dorsal to volar in the PA plane of the distal scaphoid (Figure 16.4) and a second wire in the lateral scaphoid radial to ulnar (Figure 16.5).

FIGURE 16.4 First .062–inch targeting wire placed dorsal to volar in the distal scaphoid with the wrist in ulnar deviation to extend the scaphoid.

FIGURE 16.5 Second .062–inch targeting wire placed radial to ulnar in the midlateral position of the distal scaphoid.

These wires cross at the distal scaphoid central axis and form a crosshair target for guide–wire placement (Figure 16.6a through c). To place the dorsal wire, the wrist must be ulnar deviated. This will extend the distal scaphoid fragment and will make the percutaneous perpendicular placement of the wire easier. With the wrist extended and ulna deviated, PA imaging of the dorsal scaphoid wire (if correctly perpendicular to the bone axis) will appear as a single dark point. The lateral radial wire is introduced also perpendicular to the distal scaphoid and driven toward and across the dorsal wire as it appears on image as a single point. A lateral fluroscopic image will confirm that the lateral wire has been placed in the mid–axis of the distal scaphoid.

FIGURE 16.6 (A) Cross K–wire guides for targeting of central axis guide wire. (B) AP fluoroscopic imaging of the targeting system. (C) Pronated ulnarly deviated view of the central axis with the targeting system guide wires in place.

Next, the 3,4 arthroscopic portal is identified and marked using a 19–gauge needle (Figure 16.7a and b). The 3,4 arthroscopic portal is located 1 cm distal to Lister’s tubercle and can be easily imaged using a mini–fluoroscopic unit. This is the location of the proximal scaphoid pole and the starting point for the central axis guide wire to be driven from dorsal to volar in the flexed wrist.

FIGURE 16.7 (A and B) Localization of 3–4 portal and entry site for central axis wire.

A .045–inch double–cut K–wire is placed in the 3–4 portal and impaled into the proximal scaphoid pole (Figure 16.8). Its position is confirmed fluoroscopically. Next, as the wire is driven toward the thumb base the direction is checked using the dorsal and radial guide wires (Figure 16.9). If the central axis guide wire is in the plane of both targeting wires, it will intersect the cross wires in the distal scaphoid in the central axis. This wire is usually driven through the trapezium because the scaphoid and trapezium are colinear. The wire is withdrawn volarly until the trailing end clears the radiocarpal joint, allowing the wrist to be extended (Figure 16.10).

FIGURE 16.8 Impaling of proximal scaphoid using 3–4 portal guide.

FIGURE 16.9 Driving central axis wire using cross K–wire targeting system.

FIGURE 16.10 Central axis wire withdrawn volarly to allow wrist extension for imaging.