Ans. A: Ankylosing Spondylitis The basic pathologic lesion of ankylosing spondylitis occurs at the entheses, which are sites of attachment to bone of ligaments, tendons, and joint capsules. Enthesopathy results from inflammation, with subsequent calcification and ossification at and around the entheses. Inflammation with cellular infiltration by lymphocytes, plasma cells, and polymorphonuclear leukocytes is associated with erosion and eburnation of the subligamentous bone. The process usually stas at the sacroiliac joints. Other enthesopathic sites include the iliac crest, ischial tuberosity, greater trochanter, patella, and calcaneum. Ankylosing spondylitis/ AS/ Bechterew's disease/ Bechterew syndrome/ Marie Strumpell disease/Spondyloahritis is a chronic, painful, degenerative inflammatory ahritis primarily affecting spine and sacroiliac joints, causing eventual fusion of the spine. AS is a systemic rheumatic disease and one of the seronegative spondyloahropathies. About 90% of the patients express the HLA-B27 genotype. Men are affected more than women by a ratio in excess of 10:1. Typical signs of progressed AS are the visible formation of syndesmophytes on X-rays and abnormal bone outgrowths similar to osteophytes affecting the spine. Complete fusion results in a complete rigidity of the spine, a condition known as bamboo spine. In 40% of cases, ankylosing spondylitis is associated with iridocyclitis causing eye pain and photophobia. 4.1 AS is also associated with ulcerative colitis, Crohn's disease, psoriasis, and Reiter's disease Other complications are aoic regurgitation, Achilles tendinitis, AV node block and amyloidosis & restrictive lung disease. A clinical examination and X-ray studies of the spine, which show characteristic spinal changes and sacroiliitis, are the major diagnostic tools. The Schober's test is a useful clinical measure of flexion of the lumbar spine performed during examination.