VALIDATION OF A CT BASED CLASSIFICATION OF LUMBOSACRAL SEGMENT ABNORMALITIES

Objective The purpose of this study is to describe and validate a CT based classification of lumbosacral segment abnormalities. Method 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 29s have the transverse process of L5 within 2 mm of the sacrum but not forming a joint; Type 39s have formed a diarthrodial joint, with 3A9s showing no evidence of degeneration and 3B9s displaying degenerative changes; In type 49s the transverse process and sacrum have fused; Type59s 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. Results In the study population there was an abnormality in 54.5% of individuals. In order to validate the classification the intra-observer and inter-observer ratings were analysed. The kappa values for the intra-observer results were between 0.69 and 0.88, indicating substantial agreement (using the Landis and Koch kappa interpretation). The results for inter-observer ratings also gave a combined score of over 0.7 for both sessions, again indicating substantial agreement. Conclusion A CT classification of lumbosacral segment abnormalities, which is both straight forward to use and repeatable, has been produced. The incidence of these abnormalities is higher in our population of CT scans compared to previous published series using plain radiographs.