title: Numbering of lumbosacral transitional vertebrae on MRI: role of the iliolumbar ligaments.
abstract: OBJECTIVE
  The objective of this study was to determine whether identification of the iliolumbar ligaments is of practical use for numbering lumbosacral transitional vertebrae (LSTV).
  
  
  METHODS
  Five hundred consecutive lumbar spine MRI studies were reviewed. A standard protocol of sagittal and axial T1-weighted and T2-weighted spin-echo sequences was used. The sagittal images were assessed for the presence of an LSTV, and axial images were assessed for the level of origin of the iliolumbar ligaments.
  
  
  RESULTS
  Of the 500 patients, 433 (86.6%) had normal lumbosacral segmentation and 67 (13.4%) had a transitional lumbosacral junction. The iliolumbar ligament was identified at L5 in all patients with normal lumbosacral segmentation (n = 433), bilaterally in 432 and unilaterally in one. Using the identification of the iliolumbar ligaments as a marker of the L5 vertebral level, we numbered 46 of the 67 LSTV as L5 transitions and 21 as S1 transitions.
  
  
  CONCLUSIONS
  The iliolumbar ligament is readily identifiable on axial lumbar spine MRI and always arises from L5. We suggest that its position can be used to confidently assign lumbar levels in patients with LSTV.
authors.affiliation: Department of Radiology, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, Middlesex, London, England HA7 4LP.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Hughes
authors.forename: Asif
authors.initials: A
authors.lastname: Saifuddin
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006801:Humans; D008022:Ligaments / Q000033:anatomy & histology*; D017116:Low Back Pain / Q000209:etiology; D008159:Lumbar Vertebrae / Q000002:abnormalities*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D012447:Sacrum / Q000002:abnormalities*