Authors of section

Authors

Fiesky Nuñez, Renato Fricker, Matej Kastelec, Terry Axelrod

Executive Editor

Chris Colton

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Lag screw fixation

1. Principles

Compression fracture / shearing fracture

The mechanism of this fracture is a combination of compression and shearing forces. The patient usually presents with angular deviation and malrotation.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

Use of lag screw

Be sure to insert the screw as a lag screw, with a gliding hole in the near (cis) cortex, and a threaded 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.

Long oblique and spiral shaft fractures of the proximal phalanx – Lag screw fixation

2. Approach

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

tension band wiring

3. Reduction

Reduction by ligamentotaxis

Often, the fracture can be reduced by applying traction via finger traps.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

Direct reduction

For more accurate reduction, a small pointed reduction forceps is used gently to manipulate the fracture. Application of excessive force can result in fragmentation.
Check reduction using image intensification.
Note
Anatomical reduction is important to prevent chronic instability, or posttraumatic degenerative joint disease.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

4. Fixation

Preliminary fixation by K-wire

Preliminarily fix the fragments by inserting a K-wire. Be careful to place it in such a way that it will not conflict with later screw placement.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

Screw size

Do not insert screws too close to the fracture apex or the subchondral bone. A minimal distance from the fracture line, equal to the screw head diameter, must be observed.
Screw length needs to be adequate for the screw to penetrate and purchase in the opposite (trans) cortex.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

Drilling and alternative preliminary fixation

Leaving the reduction forceps in place, drill a gliding hole as perpendicular to the fracture plane as possible, using a 1.5 (or 1.3) mm drill bit for a 1.5 (1.3) mm screw. Insert a 1.5 (1.3) mm drill sleeve into the gliding hole.
Use a 1.3 (or 1.0) mm drill bit to drill a threaded hole in the opposite fragment, just through the far (trans) cortex.

Leave the drill bit in the drill hole preliminarily to hold the reduction, if no K-wire has already been used for this purpose.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

Drill for distal screw

Drill a gliding hole for a second lag screw close to the distal apex of the fracture line. This screw, too, should be placed as perpendicularly to the fracture plane as possible, using a 1.3 (or 1.0) mm drill bit for a 1.3 (1.0) mm screw. 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 threaded hole in the opposite fragment, just through the far (trans) cortex.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

Insert proximal screw

Leaving the second drill bit in situ, insert the proximal lag screw. Do not completely tighten it at this time. The screw should just penetrate the opposite (trans) cortex.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

Insert distal lag screw

Now insert the distal lag screw. This screw, too, should just penetrate the opposite cortex.
Alternate tightening of the two lag screws helps to avoid tilting of the fragment, and applies even compression forces across the whole fracture surface.

Check using image intensification. Reduction must be anatomical.

Proximal phalanx - MCP joint - vertical shearing fracture - Lag screw fixation

5. Aftertreatment

Postoperatively

Immobilize the hand in a safe position for at least 3 weeks. This may not be necessary in the case of large fragments when the lag screw fixation is judged at operation to be absolutely stable. In that case, buddy strapping is applied immediately postoperatively.

Aftertreatment after lag-screw fixation of vertical shearing fracture at MCP joint

Follow-up

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

Functional exercises

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

lag screw fixation

Then begin with active motion exercises.

minicondylar plate fixation