This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Pelvis and Hip injuries, Subject name: Orthopaedics
The most common site of fracture neck of femur that cause Avascular necrosis is- 
Select and explain. 
A. Sub- capital zone of head of femur, B. Interochanteric zone, C. Trans-cervical area, D. Basal pa of head of femur
A: Sub- capital zone of head of femur
Answer: A: Sub- capital zone of head of femur 
Explanation: The more proximal the location of a femoral neck fracture, the more likely there is to be nonunion and/or AVN. *Thus non-union and AVN will be most common in subcapital fracture and least in basicervical fracture. M/c affects => Femoral Head M/c site => Anterolateral aspect (Being principal Wt. bearing poion) Incidence&;d/t t Steroid usage & Trauma AVN only occurs in FATTY MARROW, which contains a Sparse vascular supply. In contrast to Hematopoietic marrow which has a rich blood supply CAUSES * Trauma * Alcohol consumption * Coicosteroid intake * Gout and hyperuricemia * Hypercholesterolemia * Hypercoagulable states Hypercoisolism * Hyperlipidemia * Cushing disease * Hyperparathyroidism * Hemoglobinopathies * Intravascular coagulation (SCD;Hb S/C;Polycythemia) * Organ transplantation * Caisson disease * Pregnancy (Dysbaric osteonecrosis) * Congenital dislocation Hip * Pancreatitis * Ehlers-Danlos synd * Neoplasms * Heredity dysostosis * CRF * Legg-Calve-Pehes dis * Hemodialysis * Fabry disease * Cigarette smoking * Gaucher disease * Collagen Vascular dis * Giant cell aeritis * SLE * Thrombophlebitis * Idiopathic Ref: maheswari 9thed p.311