title: Human L3L4 intervertebral disc mean 3D shape, modes of variation, and their relationship to degeneration.
abstract: Intervertebral disc mechanics are affected by both disc shape and disc degeneration, which in turn each affect the other; disc mechanics additionally have a role in the etiology of disc degeneration. Finite element analysis (FEA) is a favored tool to investigate these relationships, but limited data for intervertebral disc 3D shape has forced the use of simplified or single-subject geometries, with the effect of inter-individual shape variation investigated only in specialized studies. Similarly, most data on disc shape variation with degeneration is based on 2D mid-sagittal images, which incompletely define 3D shape changes. Therefore, the objective of this study was to quantify inter-individual disc shape variation in 3D, classify this variation into independently-occurring modes using a statistical shape model, and identify correlations between disc shape and degeneration. Three-dimensional disc shapes were obtained from MRI of 13 human male cadaver L3L4 discs. An average disc shape and four major modes of shape variation (representing 90% of the variance) were identified. The first mode represented disc axial area and was significantly correlated to degeneration (R(2)=0.44), indicating larger axial area in degenerate discs. Disc height variation occurred in three distinct modes, each also involving non-height variation. The statistical shape model provides an average L3L4 disc shape for FEA that is fully defined in 3D, and makes it convenient to generate a set of shapes with which to represent aggregate inter-individual variation. Degeneration grade-specific shapes can also be generated. To facilitate application, the model is included in this paper׳s supplemental content.
authors.affiliation: University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Peloquin
authors.affiliation: University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Jonathon H
authors.initials: JH
authors.lastname: Yoder
authors.affiliation: University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Nathan T
authors.initials: NT
authors.lastname: Jacobs
authors.affiliation: University of Pennsylvania, Philadelphia, PA 19104, USA; GE Healthcare, Florence, SC 29501, USA.
authors.forename: Sung M
authors.initials: SM
authors.lastname: Moon
authors.affiliation: University of Pennsylvania, Philadelphia, PA 19104, USA.
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Wright
authors.affiliation: Penn State College of Medicine, Hershey, PA 17033, USA.
authors.forename: Edward J
authors.initials: EJ
authors.lastname: Vresilovic
authors.affiliation: University of Pennsylvania, Philadelphia, PA 19104, USA; University of Delaware, 125 East Delaware Ave Newark, Newark, DE 19716, USA. Electronic address: delliott@udel.edu.
authors.forename: Dawn M
authors.initials: DM
authors.lastname: Elliott
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002102:Cadaver; D003198:Computer Simulation; D020342:Finite Element Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional; D007403:Intervertebral Disc / Q000503:physiopathology*; D055959:Intervertebral Disc Degeneration / Q000503:physiopathology*; D007405:Intervertebral Disc Displacement / Q000503:physiopathology*; D008159:Lumbar Vertebrae / Q000503:physiopathology*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical
keywords: Degeneration; Intervertebral disc; Magnetic resonance imaging; Morphometry; Statistical shape model