Lag screw fixation

Avulsion fractures are the result of side-to-side (coronal) forces acting on the finger, putting the collateral ligament under sudden tension. The ligament is usually stronger than the bone, causing the ligament to avulse a fragment of bone at its insertion.
Avulsion fractures result in marked joint instability.
If the fracture is not displaced, nonoperative treatment is usually indicated (buddy taping to the adjacent finger). Displaced fractures, however, must be internally fixed.

Only avulsion fractures with large fragments can be treated with lag screws.

Be sure to insert the screw as a lag screw, with a gliding hole in the near (cis) cortex, and a thread hole in the far (trans) cortex.
Inserting a screw, across a fracture plane, that is threaded in both cortices (position screw) will hold the fragments apart and apply no interfragmentary compression.

For this procedure a dorsal approach to the MCP joint is normally used.

Reduction is achieved by pulling the finger laterally, in the direction opposite to the forces that created the fracture, and into MCP flexion, as necessary, to approximate the fragment. The avulsed fragment is pushed into place by the surgeon’s thumb.Reduction is achieved by lateral pulling of the finger in the opposite direction of the forces that created the fracture, and by MP flexion necessary for the approximation of the fragment. The avulsed fragment is pushed into place by the surgeon’s thumb.

In displaced fractures, open reduction is often necessary after preparation of a gliding hole (see later).
A small pointed reduction forceps will be used gently to reduce the fracture from palmar to dorsal and from proximal to distal. The application of excessive force can result in fragmentation.

Note
Anatomic reduction is important to prevent chronic instability or posttraumatic degenerative joint disease.

The maximal permitted diameter of the screw head is one third of the diameter of the avulsed fragment.
Screw length needs to be adequate for the screw to penetrate and purchase in the opposite cortex.

Laterally deviate the phalanx in the opposite direction to gain maximal visualization of the joint (open book).
Evaluate the fracture geometry and determine the ideal position of the gliding hole (perpendicular to the fracture plane, and through the center of the fragment).

Keeping the finger laterally deviated, drill an inside-out gliding hole through the center of the avulsed fragment.
The advantage of this technique is that it allows perfect positioning of the drill hole (perpendicular to the fracture plane and through the center of the fragment).

Note: Preserve vascularization
The risk of this procedure is the additional dissection and potential resulting devascularization, which can jeopardize fracture healing.

The avulsed fragment is now reduced anatomically, and held with a pointed reduction forceps, as previously discussed.

Insert a 1.3 (1.0) mm drill sleeve into the gliding hole.
Now use a 1.0 (0.8) mm drill bit to drill a thread hole into the opposite fragment, penetrating the far (trans) cortex.

Keeping the fragment reduced with a small reduction forceps, make a gliding hole using a 1.3 mm drill bit for a 1.3 mm screw, or a 1.0 mm drill bit for a 1.0 mm screw, from outside-in.
Insert a 1.3 (1.0) mm drill sleeve into the gliding hole.
Use a 1.0 (0.8) mm drill bit to drill a thread hole in the opposite fragment, just through the far (trans) cortex.

Insert the lag screw and tighten it. The screw should penetrate the opposite cortex.

Check under image intensification. Reduction must be anatomical.

In cases where the avulsed fragment is so small that the screw length is not sufficient to reach the far cortex, the fixation can be strengthened by adding a figure-of-eight wire loop, passing beneath the ligament insertion into the fragment.
The wire loop is also a good choice if the achieved compression is not sufficient for other reasons.

Immobilize the hand in a safe position for at least 3 weeks.

See patient 5 days after surgery to check the wound, clean and change the dressing. After 10 days, remove the sutures. Check x-rays.

Remove the splint at 3 weeks, and apply buddy strapping.

Then begin with active motion exercises.