The purpose of this study is to describe and validate a CT based classification of lumbosacral segment abnormalities. 400 CT scans were retrospectively reviewed, a classification devised and incidence of abnormalities recorded. 5 types of abnormality were identified. Type 0 is normal; Type 1 describes an asymmetrical shortening of the iliolumbar ligament; Type 2's have the transverse process of L5 within 2 mm of the sacrum but not forming a joint; Type 3's have formed a diarthrodial joint, with 3A's showing no evidence of degeneration and 3B's displaying degenerative changes; In type 4's the transverse process and sacrum have fused; Type5's have involvement of L4. In order to validate the classification, 40 scans were selected with a full cross section of types. 4 independent observers classified each scan in 2 separate sessions, 2 weeks apart.Objective
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