Morphometric Analysis of Lumbar Intervertebral Disc Height: An Imaging Study Konrad Bach 1 , Jonathan Ford 2 , Robert Foley 2 , Jacob Januszewski 1 , Ryan Murtagh 2 , Summer Decker 2 , Juan S. Uribe 3 - BACKGROUND: Little published data exist regarding normal values of disc height. Current literature relies on plain radiographs making accurate measurements of indi- vidual lumbar disc height difficult. - OBJECTIVE: We seek to establish normal values for lumbar intervertebral discs in different age groups using computed tomography scans in healthy individuals. - METHODS: Two hundred forty anonymized abdominal computed tomography scans (131 women) were prospec- tively collected once institutional review board approval was obtained. Individuals with spinal pathologies were excluded. Disc height measurements were obtained at the anterior edge, center, and posterior edge of each vertebra in the midsagittal plane, averaged, and compared against age and sex. - RESULTS: Average age was 45 (14e83) years for women and 48 (14e89) years for men. Average lumbar disc height was 5.6 Æ 1.1 mm for men and 4.8 Æ 0.8 mm for women at T12/L1, 6.9 Æ 1.3 mm for men and 5.8 Æ 0.9 mm for women at L1/2, 8.1 Æ 1.4 mm for men and 6.9 Æ 1.1 mm for women at L2/ 3, 8.7 Æ 1.5 mm for men and 7.6 Æ 1.2 mm for women at L3/4, 9.2 Æ 1.6 mm for men and 8.5 Æ 1.6 mm for women at L4/5, and 8.8 Æ 1.6 mm for men and 8.6 Æ 1.8 mm for women at L5/ S1. Disc height was significantly smaller for women than men (P < 0.001), except at L5/S1. - CONCLUSIONS: Variation in disc height is determined much more by sex than age. The maximum height of the interbody space in the adult lumbar spine was at the L4/5 level (8.9 Æ 1.7 mm [men], 8.6 Æ 1.8 mm [women]). Based on our findings, >10 mm cage height will result in supraphysiologic interbody space restoration and poten- tially predispose to complications. INTRODUCTION T he main goals of spine surgery include direct or indirect decompression of neural elements, restoration of disc height, sagittal and coronal balance, and solid fusion when indicated. Interbody fusion using an intervertebral spacer (cage) has become one of the most widely used methods for achieving these goals. However, oversized cage selection can result in increased distractive and compressive forces on end- plates, 1-4 which can predispose the patient to endplate subsi- dence, vertebral body fracture, loss of correction, and failure of the procedure with recurrence of symptomatic pathology and the need for complex revision surgery. 5-7 Inappropriate cage selection can potentially predispose the patient to unnecessary future compli- cations, and the most anatomically correct cage size should be used to avoid any such potential problems. Published data regarding normal values of disc height in the aging spine are limited. Current literature that relies on plain radiographs requires complex corrections, making accurate measurement of individual lumbar disc height difficult. 8,9 Magnetic resonance imaging data, although more easily interpreted, still relies on 2 dimensional sagittal section, and is not consistently subcategorized by lumbar level nor by decade of life. 10-13 Existing data from computed to- mography (CT) scans are similarly limited and also scarce. 14 We seek to establish normal values for lumbar intervertebral discs using novel CT scan-based vertebral modeling in healthy in- dividuals to provide a guide in the selection of interbody prosthetics. Key words - Intervertebral disc - Intervertebral disc degeneration - Lumbar intervertebral disc height - Lumbar vertebrae - Spinal fusion - Spine Abbreviations and Acronyms AP: Anterior-posterior BMI: Body mass index CT : Computed tomography FH: Foraminal height From the Departments of 1 Neurological Surgery and Brain Repair, and 2 Radiology, University of South Florida, Morsani College of Medicine, Tampa, Florida; and 3 Department of Neurosurgery, Barrow Neurological Institute, Phoenix, Arizona, USA To whom correspondence should be addressed: Konrad Bach, M.D. [E-mail: kbach@health.usf.edu] Citation: World Neurosurg. (2019). https://doi.org/10.1016/j.wneu.2018.12.014 Journal homepage: www.journals.elsevier.com/world-neurosurgery Available online: www.sciencedirect.com 1878-8750/$ - see front matter ª 2018 Elsevier Inc. All rights reserved. WORLD NEUROSURGERY -: e1-e13, - 2019 www.journals.elsevier.com/world-neurosurgery e1 Original Article