RESUMEN
<p><b>OBJECTIVE</b>To study the CT axial manifestations of iliolumbar ligament(ILL) and discusses its clinical effects on locating lumbosacral vertebral segments.</p><p><b>METHODS</b>From May 2008 to March 2010, 706 adult patients diagnosed lumbar disc disease were performed with axial scans by single slice helical CT. Among the patients, 436 patients were male and 270 patients were female, ranging in age from 25 to 82 years, the median age was 44 years, 78 cases with lumbosacral transitional vertebrae (LSTV) were verified by X-radiography or fluoroscopy. The morphology, origin and insertion, courses of ILL and the relationship of ligament and spinal segments on axial plane images were used to study. The location method of spinal segments by ILL was compared with the other four location methods on CT.</p><p><b>RESULTS</b>Of the 628 cases with normal lumbosacral segmentations sides of ligament, the main part of ILL originated from L5 transverse processes and terminated at the iliac crest, the morphological characters were divided into two types: double band (71.8%, 451/628) and single band (28.2%, 177/628). The tiny branches from posterior and outside edge of L4, lumbar disc were seen simultaneity in 3 cases. The ILL of 78 cases with LSTV all also originated from L5 transverse processes. Using ILL as a marker of the L5 vertebral level, 78 cases with LSTV were correctly numbered, the accuracy rate was higher than the other location methods, there was statistical significance between the location method by ILL and the location method by iliac crest (P < 0.05).</p><p><b>CONCLUSION</b>The main part of ILL originates from L5 transverse processes, the anatomic location is relatively steady and can be clearly displayed on axial CT, which can be used as a measure in the idenlification of LSTV in clinical practice, it is worthy to be applied widely in basic-level hospitals.</p>