In internal fixation of a spiral tibial shaft fracture, a lag screw achieves interfragmentary compression primarily because:
- A Its threads grip both fragments equally
- B It compresses the plate against the bone surface
- C It glides freely through the near cortex and grips only the far fragment, pulling the fragments together ✓
- D Its tapered tip expands the medullary canal
Correct answer: C. It glides freely through the near cortex and grips only the far fragment, pulling the fragments together
Explanation
A lag screw is inserted with an oversized glide hole in the near fragment matching the thread diameter and a smaller thread hole in the far fragment. As the screw is tightened, its threads engage only the far cortex, drawing the two fragments into compression. This converts shear forces at the fracture plane into static friction, providing absolute stability. Equal thread purchase in both fragments would hold the gap apart instead.
Reference: AO Principles of Fracture Management, 3rd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.