A comparison of stiffness and flexibility spinal testing protocols

Research output: Contribution to conferenceAbstractpeer-review


Back pain is a prevalent condition resulting in an annual cost of £500 million to the NHS. Back pain often arises from the intervertebral disc and can originate from mechanical factors (AdamsandDolan,2005). A substantial body of research, therefore, is dedicated to the biomechanical investigation of the intervertebral discs (IVDs) (Gardner-MorseandStokes, 2003). This research field has polarised into two competing protocols:stiffness and flexibility testing. From a mechanical point of view the  two are equivalent for elastic specimens. This does not hold true for non-elastic specimens, such as IVDs.The extent of any expected differences is not documented in the literature.This study investigated the effect of the two competing protocols on the reported propertie so fIVD susing acustom developed six-axis spine simulator(Holsgroveetal,2014).Abio mechanical phantom of the IVD,comprisingnylonblocksjoinedbyanitrilerubberdiscwasmanufactured.Thephantomwassubjectedtoastiffnessprotocolcharacterisedbydisplacementsof±0.5mmforanterior-posterior and lateral shear,±0.35mm for axial compression and ±1.5 degfor all rotational axes.The resulting loads were applied to the specimen subjected to the flexibility protocol.Two stiffness matrices were calculated and the diagonal elements compared.Compared to flexibility testing, stiffness testing resulted in lower values for the anterior-posterior and lateral axes, 66.0±0.9N/mmvs71.0±7.1N/mmand55.8±1.5N/mmvs59.0±2.6N/mm,respectively.The axial axis exhibited an opposite trend:311.8±17.7N/mmvs120.2±16.1N/mm. Flexibility testing resulted in lower values for all rotational degrees of freedom. Differenceswerealsorecordedfortheshapeandlinearityoftheload-displacement curve and for the area enclosed by the curve.The two testing methods produce data that cannot be easily compared.This important result demonstrates the need to standardise the protocols used to perform biomechanical studies of the spine to ensure comparisons can be made across laboratories
Original languageEnglish
Publication statusPublished - 5 Sept 2016
EventBritish Orthopaedic Research Society Annual Meeting - Glasgow University Union, Glasgow, UK United Kingdom
Duration: 5 Sept 20166 Sept 2016


ConferenceBritish Orthopaedic Research Society Annual Meeting
Country/TerritoryUK United Kingdom


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