<prompt> Least common joint to be affected in ankylosing spondylitis is:Sacroiliac jointTemporomandibular jointCostovertebral jointHip joint  <response>: Ans: B Temporomandibular joint Ref: Harrisons Principles of internal Medicine, 18th edExplanation:Sacroiliitis is often the earliest manifestations of ASAS 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. 