I. Systemic Factors 1. Age 2. Activity level including General immobilization Space flight 3. Nutritional status 4. Hormonal factors Growth hormone Corticosteroids (microvascular osteonecrosis) Others (thyroid, estrogen, androgen, calcitonin, PTH, prostaglandins) 5. Diseases: DM, anemia, neuropathies, tabes 6. Vitamin deficiencies: A, C, D, K 7. Drugs: nonsteroidal antiinflammatory drugs (NSAIDs), anticoagulants, factor XIII, calcium channel blockers (verapamil), cytotoxins, diphosphonates, phenytoin (Dilantin), sodium fluoride, tetracycline 8. Other substances (nicotine, alcohol) 9. Hyperoxia 10. Systemic growth factors 11. Environmental temperature 12. Central nervous system trauma II. Local Factors A. Factors independent of injury, treatment, or complications 1. Type of bone 2. Abnormal bone Radiation necrosis Infection Tumors & other pathological condns 3. De