Secondary Logo

Journal Logo

Institutional members access full text with Ovid®

The Influence of Concordant Complex Posture and Loading Rate on Motion Segment Failure

A Mechanical and Microstructural Investigation

Schollum, Meredith L., PhD; Wade, Kelly R., PhD; Shan, Zhi, MD; Robertson, Peter A., MD; Thambyah, Ashvin, PhD; Broom, Neil D., PhD

doi: 10.1097/BRS.0000000000002652
BIOMECHANICS
Buy

Study Design. Microstructural investigation of compression-induced herniation of a lumbar disc held in a concordant complex posture.

Objective. To explore the significance of loading rate in a highly asymmetric concordant posture, comparing the mechanisms of failure to an earlier study using a nonconcordant complex posture.

Summary of Background Data. A recent study with a nonconcordant complex posture (turning in the opposite direction to that which the load is applied) demonstrated the vulnerability of the disc to loading that is borne by one set of oblique-counter oblique fiber sets in the alternating lamellae of the annulus, and aggravated by an elevated loading rate. Given the strain rate–dependent properties of the disc it might be expected that the outcome differs if the posture is reversed.

Methods. Forty-one motion segments from ovine 16 spines were split into two cohorts; adopting the previously employed low rate (40 mm/min) and surprise rate (400 mm/min) of loading. Both groups of damaged discs were then analyzed microstructurally.

Results. With the lower rate loading the concordant posture significantly reduced the load required to cause disc failure than earlier described for nonconcordant posture (6.9 vs. 8.4 kN), with more direct tears and alternate lamella damage extending to the anterior disc. Contrary to this result, with a surprise rate, the load at failure was significantly increased with the concordant posture (8.08 vs. 6.96 kN), although remaining significantly less than that from a simple flexed posture (9.6 kN). Analysis of the damage modes and postures suggest facet engagement plays a significant role.

Conclusion. This study confirms that adding shear to the posture lowers the load at failure, and causes alternate lamella rupture. Load at failure in a complex posture is not determined by loading rate alone. Rather, the strain rate–dependent properties of the disc influence which elements of the system are brought into play.

Level of Evidence: N/A

Department of Chemical and Materials Engineering, Experimental Tissue Mechanics Laboratory, University of Auckland, Auckland, New Zealand

Department of Orthopaedic Surgery, Sir Run Run Shaw Hospital, Zhejang University, Hangzhou, China

Department of Orthopaedic Surgery, Auckland City Hospital, Auckland, New Zealand.

Address correspondence and reprint requests to Meredith L. Schollum, PhD, Department of Chemical and Materials Engineering, University of Auckland, Private Bag 92019, Auckland 1142, New Zealand; E-mail: Meredith.schollum@auckland.ac.nz

Received 3 November, 2017

Revised 6 March, 2018

Accepted 13 March, 2018

The manuscript submitted does not contain information about medical device(s)/drug(s).

NuVasive funds were received in support of this work.

Relevant financial activities outside the submitted work: consultancy, grants.

Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.