Bamboo spine with sacroilitis is a feature of which of the following seronegative ahritis ?

Ankylosing spondylitis: Chronic disorder characterised by a progressive inflammatory stiffening of joints with predliction for joints of axial skeleton,especially sacroiliac joints. C/f: classic presentation- youngvadukt,15-30 years old,presenting with gradual onset of pain and stiffness of lower back.paib tends to be worse at night or early morning ,awakening from sleep.He gets better only after he walks.later kyphotic deformity of spine and deformity of hips may be prominent. On X ray- *squaring of veebrae: normal anterior concavity of veebral body is lost due to calcification of anterior longitudinal ligament. *loss of lumbar lordosis. *bridging osteophytes-syndesmophytes. *bamboo spine appearence. Other features: ESR- elavated Hb-mild anemia image - xray shows bamboo spine REF:Essential Ohopaedics.Maheswari &Mhaskar.Edition 9.Pg no:293