There is very little written about the Sacro-Iliac joint (S.I.) in medical books on backache. As Orthopaedic and Neurosurgical residents are not taught to consider S.I. dysfunction as a cause of back pain, it is not surprising that surgeons know little of diagnosis and treatment. The structure of the S.I. joint is confusing; the upper posterior ligamentous portion is a space in which the sacrum and ilium are not in contact, while the anterior and lower half is a typical synovial joint lined with hyaline cartilage. It is neither hinge nor ball and socket, rather, a sliding joint with motion too small to measure, so it is overlooked as a moving joint, vulnerable to injury. Its nerve supply is from L2 to S3 and pain may be well localized with referral to the groin, or distally into the leg as an ill-defined sensation radiating to the toes. [Read more…]