In the Pauwels classification of intracapsular femoral neck fractures, the fracture line makes an angle of more than 50 degrees with the horizontal plane. This fracture carries the poorest prognosis primarily because:
- A The vertically oriented fracture line is subjected to shearing forces that resist impaction and healing ✓
- B It is always associated with an acetabular fracture
- C It occurs exclusively in osteoporotic bone with poor screw purchase
- D It is invariably an open fracture with high infection risk
Correct answer: A. The vertically oriented fracture line is subjected to shearing forces that resist impaction and healing
Explanation
Pauwels classified neck fractures by the angle the fracture line makes with the horizontal: Type I under 30 degrees, Type II 30 to 50 degrees, Type III over 50 degrees. As the angle becomes more vertical, compressive forces across the fracture are replaced by shearing forces, which prevent impaction and promote nonunion and displacement. The other options describe features that do not define this system.
Reference: Rockwood and Green's Fractures in Adults, 9th ed.
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