Percutaneous and Arthroscopic-Assisted Scaphoid Fixation

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Percutaneous screw insertion has become commonplace in the treatment of undisplaced scaphoid waist fractures and nonunions. Numerous investigators have demonstrated faster union rates and improved wrist motion compared with open screw insertion, since percutaneous methods prevent the need for a capsulotomy, which spares the carpal ligaments and results in less interference with the scaphoid blood supply. There are some instances in which an arthroscopic assist can be useful. Arthroscopy is a useful adjunct for gauging the starting point for guidewire placement with dorsal screw insertion. It is a valuable aid in assessing the quality of the fracture reduction, in guarding against screw cutout, and in evaluating the rigidity of fixation, since seemingly good screw purchase may not adequately stabilize a comminuted segment. Arthroscopy also allows one to assess and treat any additional soft tissue lesion.

The fracture position is first assessed with anteroposterior, lateral, and oblique x-rays, although a computed tomography (CT) scan is helpful in difficult cases. Dorsal screw insertion is recommended for scaphoid fractures of the proximal pole and waist because this permits maximum fracture compression, whereas distal pole fractures are best approached through a volar percutaneous approach. Volar implantation often requires eccentric screw placement through the distal pole, since one has to ream through the trapezium to gain access to the central scaphoid axis. However, the screw can still be placed centrally through the waist and proximal pole ( Fig. 20-1 A and B). The guidewire insertion is integral to the procedure and directly impacts the outcome, since screws that are placed along the central axis are stronger and have faster union rates than eccentrically placed screws. Insertion down the central axis also permits insertion of a longer screw ( Fig. 20-1 C), which is desirable because biomechanical data have shown that a longer screw distributes and reduces the bending forces more efficiently. Stable fixation, however, is the key to fracture healing, since eccentric screw fixation can still result in union ( Fig. 20-2 ).

INDICATIONS

The indications for percutaneous scaphoid screw insertion parallel those for an open reduction. These include any acute displaced proximal pole or waist fracture of the scaphoid with more than 1 mm of displacement or translation, or any fractures with significant comminution or angulation. Nondisplaced fibrous scaphoid nonunions without evidence of avascular necrosis are also suitable candidates ( Fig. 20-3 ).

CONTRAINDICATIONS

Partial or complete avascular necrosis of the scaphoid is a relative contraindication to percutaneous techniques, although scaphoid union has been described with this approach. A small proximal pole fragment does not allow adequate screw purchase and may fragment. Scaphoid nonunions with a humpback deformity and secondary dorsal intercalated segmental instability (DISI) deformity require an open volar wedge graft. The presence of significant radiocarpal and/or midcarpal degenerative changes mandates an alternate approach.

SURGICAL TECHNIQUE

Dorsal Approach

Guidewire insertion is accomplished free-handed and percutaneously using fluoroscope control, initially without tourniquet. For fractures of the proximal pole and waist, the author favors the dorsal percutaneous technique popularized by Joseph Slade and colleagues. The fluoroscopy unit is positioned over the arm board, vertical to the floor. The wrist is flexed 45 degrees over folded towels, which places the scaphoid axis at 90 degrees to the beam ( Fig. 20-4 A and B). Slade has described the use of Kirschner (K) wires inserted in the distal scaphoid pole as an external cross K-wire scaphoid guide. I prefer to insert the K wires in the scaphotrapezial (ST) joint. The first guidewire is placed dorsally into the scaphotrapezial joint to the midpoint of the trapezium. A second guidewire is inserted radially into the scaphotrapezial joint to the midpoint of the trapezium. The starting point for the guidewire is at the most proximal tip of the scaphoid pole immediately adjacent to the scapholunate interosseous ligament (SLIL). A K wire is inserted directly into the scapholunate interval as an aid to finding this point ( Fig. 20-5 A and B). Alternatively, the arthroscope can be placed in the 3-4 portal, and the starting point can be guided to the soft spot on the proximal pole that borders the insertion of the scapholunate interosseous ligament on the scaphoid.

The guidewire is then driven from dorsal to volar while keeping the wrist flexed. Aiming toward the dorsal scaphotrapezial K wire on an anteroposterior fluoroscopic view guides the medial/lateral alignment of the guidewire. Aiming toward the radial scaphotrapezial K wire on a semipronated lateral view guides the dorsal/volar alignment. The guidewire is then driven distally through the trapezium and out through the skin until the trailing end clears the radiocarpal joint, which allows the wrist to be extended. If the fracture is displaced, the guidewire is advanced distally until it lies solely within the distal fragment.

Percutaneous 0.62-inch K wires can then be inserted into the proximal and distal fragments and used as joysticks to align the scaphoid ( Fig. 20-6 ). The alignment of the concave scaphoid surface can be used as a reference for fracture reduction. This reduction is captured by driving the guidewire proximally. A second antirotation K wire should be inserted before reaming. The reamer is then introduced over the guidewire.

The arm is exsanguinated and the tourniquet is elevated at this point. The arm is suspended in a traction tower with 10 pounds of traction, and the quality of the fracture site reduction is visualized arthroscopically through the midcarpal ulnar (MCU) portal, with the probe in the midcarpal radial (MCR) portal. After the arthroscopic assessment, the wrist is taken out of traction and flexed. The screw lengths can be gauged by driving the guidewire dorsally until the trailing end is in the subchondral bone of the distal scaphoid pole. A second wire of equal length is placed percutaneously at the proximal scaphoid pole and parallel with the guidewire. The difference in length between the trailing end of each wire is the scaphoid length. The screw length selected should be 4 mm less than the scaphoid length. This permits 2 mm of clearance of the screw at each end of the scaphoid, thus ensuring complete implantation without screw exposure ( Fig. 20-7 ). A recent anthropometric study determined that the average scaphoid length in adult males was 31.3 mm ± 2.1, whereas the average female scaphoid was 27.3 mm ± 1.7; hence the longest screw lengths may range from 23 to 27 mm.