Direct measurement of intervertebral disc maximum shear strain in six degrees of freedom: Motions that place disc tissue at risk of injury

Abstract

Human intervertebral disc specimens were tested to determine the regions of largest maximum shear strain experienced by disc tissues in each of three principal displacements and three rotations, and to identify the physiological rotations and displacements that may place the disc at greatest risk for large tissue strains and injury. Tearing of disc annulus may be initiated by large interlamellar shear strains. Nine human lumbar discs were tagged with radiographic markers on the endplates, disc periphery and with a grid of wires in the mid-transverse plane and subjected to each of the six principal displacements and rotations. Stereo-radiographs were taken in each position and digitized for reconstruction of the 3-D position of each marker. Maximum tissue shear strains were calculated from relative marker displacements and normalized by the input displacement or rotation. Lateral shear, compression, and lateral bending were the motions that produced the mean (95% confidence interval) largest regional maximum shear strains (MSS) of 9.6 (0.7) %/mm, 9.0 (0.5) %/mm, and 5.8 (1.6) %/° respectively, and which occurred in the posterior, posterolateral and lateral peripheral regions of the disc. After taking into account the reported maximum physiological range of motion for each degree of freedom, motions producing the highest physiological MSS were lateral bending (57.8 (16.2)%) and flexion (38.3 (3.3)%), followed by lateral shear (14.4 (1.1)%) and compression (12.6 (0.7)%).

Flexibility of the Lumbar Intervertebral Disc in Bending and Torsion: Experimental and Finite Element Study

“…Thus, degenerated discs develop higher stresses while normal discs develop higher strains. Bending simulation shows that flexion, extension, right and left lateral loading causes convex and concave curvature in the disc, which implies combine tensile and compression stresses and higher strains which occurred in the disc posterior side, as reported elsewhere [24][25][26]. Torsion simulation showed large shearing in the annulus periphery, suggesting a main load carrier upon removal of posterior elements, as previously suggested by Refs.…”

A review of the application of reinforced hydrogels and silk as biomaterials for intervertebral disc repair

“…Gellan gum is bacterialderived and shows extremely high cytocompatibility in vitro and in vivo (Ahearne and Kelly, 2013;Anderson et al, 1988;Khang et al, 2015;Reitmaier et al, 2014). Recently, this material was reinforced to withstand higher compressive forces by addition of methacrylated modifications, resulting in a much stiffer hydrogel tuneable in the range of 0.15-148 kPa (Coutinho et al, 2010). This is similar to the crosslinking genipin approach that leads to shear stiffness in the range of 47-61.1 kPa, depending on the genipin concentration or up to 73 kPa, when fibrin is combined with genipin and fibronectin (Guterl et al, 2014).…”

“…For example, normal movement causes intradiscal pressures in the range of 0.1 MPa when reclining, 0.46 MPa for unsupported sitting, and 0.5 MPa for relaxed standing (Nachemson and Elfstrom, 1970;White and Panjabi., 1990;Wilke et al, 1999). Hence, a successful approach has to incorporate a biomaterial that can fulfil the requirements of withstanding a motion in six degrees of freedom (Costi et al, 2007;Guterl et al, 2013;Long et al, 2016b;Nerurkar et al, 2010), while providing nutrient delivery to the centre of the IVD and simultaneously allowing the transportation of metabolites out of the disc Kandel et al, 2008). Due to this challenging task, approaches that rely solely on biomaterials to restore disc height are more closely investigated.…”

“…This is similar to the crosslinking genipin approach that leads to shear stiffness in the range of 47-61.1 kPa, depending on the genipin concentration or up to 73 kPa, when fibrin is combined with genipin and fibronectin (Guterl et al, 2014). For instance, for NP repair it was shown by Silva-Correia, et al (2012) that rabbit NP cells thrive perfectly for an extended period, without much loss of cell viability, in methacrylated Gellan gum (Coutinho et al, 2010;Khang et al, 2015;Silva-Correia et al, 2011; Silva- Table 1. List of previous research articles and reviews using fibrin hydrogels for either AF and NP repair or 3D culture of these cells.…”

Influence of End-Plates on Biomechanical Response of the Human Lumbosacral Segment

“…In particular, the interface between intervertebral discs and vertebral surfaces represents the most critical region for the onset of spinal diseases. Moreover, some recent studies (Costi et al, 2007;Wilson et al, 2003) showed how the shear effects are dominant in disc tissue failures. For these reasons, it was considered interesting to plot, for the more stressed disc, in Panjabi configuration (Panjabi et al 1994), the maps of the maximum shear stress for flexion and extension moments and to compare the distributions for the two models, with and without endplates, in order to underline how the presence of the endplates allow the reduction of the stress condition in the intervertebral disk.…”