This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Fracture Neck of Femur, Subject name: Orthopaedics
Fracture neck femur cause of non-union- 
Select and explain. 
A. Injury to blood supply with shearing stress, B. Poor nutrition of the patient, C. Smoking, D. Old age and osteoporosis
A: Injury to blood supply with shearing stress
Answer: A: Injury to blood supply with shearing stress 
Explanation: Ans. is 'a' i.e., Injury to blood supply with shearing stresso Causes of non-union in fracture neck of femur are :-Fracture morphology - high fracture angle and increased shear.Displaced fracture grade 3/4.Fracture comminution.Inadequate reduction and stability of fixation.Poor bone quality.Injury to vascularity- direct and tamponade effect.Absence of cambium layer in periosteum.Factors in synovial fluid which inhibit the callus formation.Lack of hematoma.Washing away and dilution of osteogenic factors.