A 55-year-old man is operated for an intertrochanteric fracture of the femur with a dynamic hip screw (DHS). Which anatomical feature determines the position of the lag screw and is critical for stable fixation?
- A The barrel of the DHS should engage the lesser trochanter
- B The lag screw must be placed in the centre-centre position on AP and lateral views in the femoral head ✓
- C The plate should span at least three cortices above the fracture
- D The lag screw tip should lie within 5 mm of the calcar femorale
Correct answer: B. The lag screw must be placed in the centre-centre position on AP and lateral views in the femoral head
Explanation
Tip-apex distance (TAD) is the gold standard measurement: a TAD less than 25 mm (sum of distances from screw tip to apex of femoral head on AP and lateral views) predicts a very low cut-out rate. The ideal position is centre-centre on both views, placing the screw in the strongest trabecular bone (Ward's triangle apex / central head). Backing out and cut-out are the most common implant failures.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.