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Effects of Endplate Removal on the Structural Properties of the Lower Lumbar Vertebral Bodies

Oxland, Thomas R., PhD*; Grant, J. Pamela, MASc*; Dvorak, Marcel F., MD; Fisher, Charles G., MD

doi: 10.1097/01.BRS.0000060259.94427.11
Biomechanics

Study Design. A biomechanical investigation using indentation tests in human cadaveric lumbar vertebrae.

Objectives. To determine the effect of endplate removal on the structural properties across the lower lumbar vertebral bodies (L3–L5).

Summary of Background Data. The structural properties of the vertebral endplates exhibit substantial regional variation. In addition, several recent studies of the endplate-implant interface have suggested that the endplate is not a significant structural element.

Methods. The bony endplates on the left or right side of seven intact human vertebrae (L3–L5) were removed with a high-speed burr. Indentation tests were performed at standardized test sites on both sides of the endplate using a 3-mm diameter, hemispherical indenter with a test rate of 0.2 mm/s to a depth of 3 mm. The failure load and stiffness at each site were determined from the load-displacement curves. Three-way repeated measures analyses of variance were used to analyze the resulting data for variation in the anterior-posterior and lateral directions, as well as to determine the effect of endplate removal.

Results. For the intact endplates, both the failure load and stiffness varied significantly across the endplate surfaces (P < 0.0001), with the posterolateral regions being stronger and stiffer than the central regions. With endplate removal, the mean failure load decreased to about 33% of the intact failure load, a significant drop (P = 0.04), and there was a trend toward greater decreases posteriorly (P = 0.05). With endplate removal, the mean stiffness also decreased significantly (P = 0.01), with the greater decreases occurring laterally (P = 0.04).

Conclusions. There was a significant effect of endplate removal on the local structural characteristics of the vertebral endplate.

From the *Division of Orthopaedic Engineering Research and the †Division of Spine, Departments of Orthopaedics and Mechanical Engineering, University of British Columbia and Vancouver Hospital and Health Sciences Centre, Vancouver, British Columbia, Canada.

Acknowledgement date: February 19, 2002.

First revision date: June 17, 2002.

Second revision date: September 10, 2002.

Acceptance date: September 16, 2002.

Device status/drug statement: This report does not contain information about medical device(s) or drug(s).

Conflict of interest: No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this report.

Address reprint requests to Thomas R. Oxland, PhD, 3114 - 910 West 10th Avenue, Vancouver, BC, Canada, V5Z 4E3. E-mail: toxland@interchange.ubc.ca

© 2003 Lippincott Williams & Wilkins, Inc.