1 Introduction topenlarge
When using internal fixation, bone healing is quicker than in nonoperative treatment, and the period of postoperative immobilization is shortened.
Percutaneous (minimally invasive) treatment brings the advantages of internal fixation without the disadvantages of a wide surgical approach, e.g. preserving the palmar ligament complex, and local vascularity, and avoiding postoperative immobilization.
Conventional radiographs do not adequately demonstrate the complete fracture configuration. A CT scan is strongly recommended if a percutaneous procedure is planned.
80% of the surface of the scaphoid is covered with articular cartilage. This greatly limits potential points of entry for fixation devices.
An additional constraint is the curved shape of the scaphoid.
This means that a wire, or fixation device, along the true central axis of the scaphoid is not possible from a palmar approach. Occasionally, access to a distal entry point for a device can only be gained by a limited excavation of the edge of the trapezium.
Confirm the fracture pattern
Before starting the surgical procedure, re-examine the fracture pattern under the image intensifier. Be sure that the fracture is suitable for percutaneous technique, and that no secondary displacement has occurred.
2 Preliminary reduction topenlarge
Percutaneous fixation is largely indicated for undisplaced or minimally displaced fractures of the waist of the scaphoid.
Hyperextension and ulnar deviation of the wrist will facilitate any necessary reduction of the fracture.
Hyperextension also assists in bringing the trapezium dorsal to the insertion point of the guide wire, at the scaphoid tubercle.
3 Skin incision topenlarge
A short stab incision is made distally to the scaphotrapezial joint.
For a complete description of the landmarks and the siting of this incision, click here.
4 Insertion point for the guide wire topenlarge
Use a hypodermic needle to determine the insertion point radiologically before inserting the threaded guide wire.
The insertion point is on the distal surface of the scaphoid tubercle, at the edge of the scaphotrapezial joint.
Insertion of guide wire
The threaded guide wire is inserted at the confirmed entry point through a drill guide.
If no drill guide is available, use a protective sleeve.
The guide wire track must be angled 45 degrees dorsally, and 45 degrees medially, along the mid-axis of the scaphoid.
The position of the wire should be as perpendicular as possible to the fracture line. In oblique fractures, this principle may have to be compromised.
Do not penetrate beyond the proximal cortex of the scaphoid.
5 Fixation topenlarge
Measuring the length
Two methods can be employed for measuring the desired screw length:
- Insert the dedicated measuring device over the guide wire, through the drill guide, which must be firmly positioned on the tubercle for a reliable measurement.
- If the dedicated drill guide is not available, take another guide wire of the same length and place its tip onto the bone at the insertion point. The difference in length between the protruding ends of the two wires indicates the length of the drill hole for the screw.
Subtract 2 mm to determine the screw length.
Drilling and tapping
Use only the dedicated drill bit. A power drill will exert a smaller and more controlled force on the fragments than manual drilling, and will reduce the risk of displacing the fragments. A small power drill with slow rotation is preferable.
Use Ringer lactate solution to cool the drill bit, in order to minimize thermal injury.
Check the position of the tip of the drill bit using image intensification.
Tap the drill hole manually if not using self-tapping screws.
Insert the screw manually over the guide wire.
It is vital that the threaded section of the tip of the screw pass completely beyond the fracture plane, if interfragmentary compression is to be achieved.
Before final tightening, remove the guide wire.
Make sure that the threads at the near end of the screw are fully buried in the bone at the insertion site. Make sure that all threads on the far side have crossed the fracture plane in order to ensure interfragmentary compression.
Check the final position of the screw and the scaphoid stability using image intensification.