Lag Screw

Lag screw operative technique

This is a procedure that you should be able to talk through and perform this skill during the ST3 Ortho interview process. It is possible that this could for a part of the technical skills station. However you are likely to need to do more than just a lag screw during the technical skills assessment. When practicing these skills just think what could be on the marks sheet. You will receive marks for telling the assesses what you are doing and the rationale behind it.

A screw is placed perpendicular (at a right angle) to the plane of the fracture to produce interfragmentary compression.
If the screw is not perpendicular to the fracture it will displace the fragments.

Commonly used in distal fibula fractures, medial malleolus fractures, or to repair an osteotomy. When used in fixation of distal fibula fractures a 1/3 tubular plate is used in neutralization mode to avoid displacement whilst bony union occurs.

I would perform a lag screw as follows in an appropriately marked and consented patient having pre-operatiely reviewed the patient and there radiographs to ensure the operation is indicated.

Pre op
Team brief (equipment i.e small or large fragment set), antibiotics as per trust protocol (IV Teicoplanin 400mg & Gentamicin 80mg), potentially image intensifier if part of a larger procedure, & patient position)

WHO Safer surgery checklist
Prep and drape the limb above the level of operation
Approach to bone
Dissection of fracture ends to remove any soft tissue interposition / small potentially non viable fragments
Reduce fracture using pointed bone reduction forceps (placed in the plane of the lag screw but not in the way)
Position drill with tissue protector
Drill near cortex perpendicular to fracture to create sliding hole (3.5mm small fragment for fibula)
Place tower / drill guide in hole and drill far cortex with smaller drill (2.7mm small fragment for fibula) to create thread hold
Measure (screw should protrude far cortex by 2mm)
Tap far / thread cortex (use soft tissue protector)
Countersink sliding hold to create a larger surface area for head to apply compression over
Insert screw along axis of drilled hole
At this point if your lag screw has been positioned correctly you will see a small amount of blood be squeezed out of the fracture site
Remove pointed bone clamp

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