This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General anatomy, Subject name: Anatomy
[{'content': "Heterotrophic calcification occurs in \nSelect and explain. \nA. Ankylosing spondylitis, B. Rieter's syndrome, C. Forrestier disease, D. Rheumatic ahritis", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ref Robbins 7/e p 41_42, Harrison 17/e p1952 Heterotopic ossification (HO) is the presence of bone in soft tissue where bone normally does not exist. The acquired form of HO most frequently is seen with either musculoskeletal trauma, spinal cord injury, or central nervous system injury. For example, patients who have recently undergone total hip ahroplasty or have paraplegia after spinal cord injury are at risk for HO. The fever, swelling, erythema, and occasional joint tenderness seen in early HO can be difficult to distinguish from cellulitis, osteomyelitis, or thrombophlebitis. Bone scanning and other imaging tests frequently are used to distinguish between these diagnostic possibilities', 'role': 'assistant'}]