title: Cranio-caudal asymmetries in trabecular architecture reflect vertebral fracture patterns.
abstract: Clinically, vertebral fractures often occur in the upper lumbar spine and involve the superior endplate of a vertebra (which is immediately caudal to a disc). Knowledge that the cranial endplate of a disc is thicker and has greater bone mineral density (BMD) than the corresponding caudal endplate helps to explain this phenomenon. In this study, we investigated structural differences in vertebral trabeculae on either side of a lumbar disc to provide further insight into vertebral fracture risk. As the focus is trabecular difference within a spinal motion segment, we define cranial and caudal vertebral trabeculae relative to the disc. Ninety-two spinal motion segments from 46 cadaveric lumbar spines (males, mean age 50years, range 21-63years) were studied. Disc narrowing on radiography and spread of barium sulfate (BaSO4) on discography were measured to indicate disc degeneration. Micro-computed tomography (μCT) images were obtained at a resolution of 82μm for each vertebra and processed to include only vertebral trabeculae. Using image processing, the vertebral trabeculae were divided into superior and inferior halves, and then into central and peripheral regions which were approximately opposite to the disc pulposus and annulus, and further into anterior and posterior sub-regions. Microarchitecture measurements for each vertebral region were obtained to determine the differences between the cranial and caudal trabeculae (relative to disc) and their associations with age and disc degeneration within each spinal motion segment. Data from the upper (L1/2-L3/4) and lower (L4/5) lumbar segments were analyzed separately. In the upper lumbar region, the trabeculae cranial to a disc on average had 5.3% greater BMD and trabecular bone volume, 3.6% greater trabecular number, 9.7% greater connectivity density, and 3.7% less trabecular separation than the corresponding caudal trabeculae (P<0.05 for all). Similar trends were observed in peripheral, anterior and posterior regions, but not in central region. No structural difference was observed in the trabeculae of L4/5 segment. Structural asymmetries of vertebral trabeculae were not associated with age, disc degeneration, or disc narrowing. Vertebral trabecular parameters cranial to the disc were greater than caudally in the upper but not in the lower lumbar region. Findings further explain why vertebral fractures are more common in the upper lumbar region and more frequently involve the endplate caudal to a disc.
authors.affiliation: Spine lab, Department of Orthopedic Surgery, The First Affiliated Hospital of Zhejiang University, Hangzhou, China.
authors.forename: Ge
authors.initials: G
authors.lastname: Yang
authors.affiliation: Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Canada.
authors.forename: Michele C
authors.initials: MC
authors.lastname: Battié
authors.affiliation: Cumming School of Medicine, University of Calgary, Calgary, Canada.
authors.forename: Steven K
authors.initials: SK
authors.lastname: Boyd
authors.affiliation: Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, Canada.
authors.forename: Tapio
authors.initials: T
authors.lastname: Videman
authors.affiliation: Spine lab, Department of Orthopedic Surgery, The First Affiliated Hospital of Zhejiang University, Hangzhou, China. Electronic address: wangyuespine@gmail.com.
authors.forename: Yue
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000328:Adult; D000071556:Cancellous Bone / Q000473:pathology*; D006801:Humans; D055959:Intervertebral Disc Degeneration / Q000473:pathology; D008159:Lumbar Vertebrae / Q000473:pathology; D008875:Middle Aged; D012886:Skull / Q000473:pathology*; D016103:Spinal Fractures / Q000473:pathology*; D055815:Young Adult
keywords: Disc degeneration; Lumbar spine; Trabecular microstructure; Vertebral fractures; μCT