Ratcheting Behavior of Intervertebral Discs Under Cyclic Compression: Experiment and Prediction.

Chun‐qiu Zhang,Lilan Gao,Xin Wang,Qing Liu,Cheng‐fei Du,Tao Zhang,Hai‐ying Liu

doi:10.1111/os.12530

Abstract

ObjectiveTo evaluate the ratcheting behavior of intervertebral discs (IVD) by experiments and theoretical study.MethodThe lumbar spines of sheep were obtained at a local slaughterhouse, and the IVD was processed with upper and lower vertebral bodies (about 5 mm) to ensure the mechanical state of the IVD in situ. The ratcheting tests of uniaxial cyclic compression loading for disc samples is carried out using the Electronic Universal Fatigue Testing System at room temperature. The effects of different stress variations, stress rates, as well as different segments on ratcheting behavior of discs were investigated.ResultsThe ratcheting strain evolution of lumbar IVD include stages of sharp increase and asymptotic stability. Both the ratcheting strain and ratcheting strain rate increase with an increase of stress variation (R = 0.962, P = 0.004) but decrease with an increase of the stress rate (R = −0.876, P = 0.019 ). Compression stiffness increases with an increase of the stress rate (R = 0.964, P = 0.004 ) or stress variation (R = 0.838, P = 0.037). Compared with L5 – 6, the L6 – 7 disc showed less ratcheting strain (P = 0.04 ), indicating that the disc at this segment was more resistant to the impact of the ratcheting cycle. In addition, ratcheting strain evolution was predicted using a ratcheting evolution constitutive equation, and the predicted results were in good agreement with experimental data.ConclusionsThe ratcheting behavior occurs in IVD, and this cumulative deformation is consistent with the general ratcheting behavior. The constitutive equation can predict the ratcheting strain evolution of IVD very well. These results are of great significance for the analysis of defects and the development of repair in IVD.

Highlights

Lumbar degenerative disc disease is one of the most common orthopaedic diseases
Some research has investigated the mechanical properties of intervertebral discs (IVD)
The purpose of the present study is to evaluate the ratcheting behavior of IVD under uniaxial cyclic compression (Fig. 1), the effects of stress variations and stress rates on the ratcheting behavior, and the differences between the ratcheting responses of L5–6 and L6–7 discs

Summary

Introduction

Lumbar degenerative disc disease is one of the most common orthopaedic diseases. It is characterized by loss of water in disc tissues, decrease of internal pressure, rupture of internal structure of nucleus pulposus, and annulus fibrosus. Some research has investigated the mechanical properties of intervertebral discs (IVD). The stress/strain characteristics of different regions of the lumbar IVD under static loading have been tested in vitro, and the relationship between the structure of the disc and its mechanical properties have been analyzed. O’Connell et al.[2] measured the internal deformation of non-degenerative and degenerative human IVD during flexion and tension under axial compression load, and analyzed the effects of different regions of the disc, loading position, and degeneration on the mechanical properties of lumbar

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