A 27 year old male presents with low backache that occurs early in the morning assosciated with stiffness, and persists for more than 30 minutes.On examination his chest expansion is also restricted. The most probable diagnosis is

Ankylosing spondylitis causes destruction of aicular cailage and bony ankyloeis, especially of the sacroiliac and aprophyseal joints(between tuberosities and processes). It is also known as rheumatoid spondylitis and Mqrir-Strumpell disease.Disease involving sacroiliac joints and veebrae become symptomatic in the second and third affected individuals.