This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other Rheumatic Diseases, Subject name: Orthopaedics
[{'content': 'Least common joint to be affected in ankylosing spondylitis is: \nSelect and explain. \nA. Sacroiliac joint, B. Temporomandibular joint, C. Costovertebral joint, D. Hip joint', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans: B (Temporomandibular joint) Ref: Harrison\'s Principles of internal Medicine, 18th edExplanation:"Sacroiliitis is often the earliest manifestations of AS"AS primarily affects the axial skeleton and peripheral jointsCommon sites include the:Sacroiliac jointCostostemal junctionsSpinous processesIliac crestsGreater trochantersIschial tuberositiesTibial tuberclesHeelsArthritis in the hips and shoulders ("root" joints) occurs in 25-35% of patients.Severe isolated hip arthritis or bony chest pain may be the presenting complaint.', 'role': 'assistant'}]