参考答案：A

解析：Bone fracture is a major complication of osteoporosis that results when loss of calcium and phosphate increases the fragility of bones. Estrogen deficiencies result from menopause--not osteoporosis. Calcium and vitamin D supplements may be used to support normal bone metabolism, but a negative calcium balance isn’t a complication of osteoporosis. Dowager’s hump results from bone fractures. It develops when repeated vertebral fractures increase spinal curvature.