The Dynesys, a flexible posterior stabilization system that provides an alternative to fusion, is designed to preserve intersegmental kinematics and alleviate loading at the facet joints. Recent biomechanical evidence suggests that the overall range of motion (ROM) with the Dynesys is less than the intact spine. The purpose of this investigation was to conduct a comprehensive characterization of the three-dimensional kinematic behaviour of the Dynesys and determine if the length of the Dynesys polymer spacer contributes to differences in the kinematic behaviour at the implanted level. Ten cadaveric lumbar spine segments (L2-L5) were tested by applying a pure moment of +/-7.5 Nm in flexion-extension, lateral bending, and axial rotation, with and without a follower preload of 600 N. Test conditions included: (a) intact; (b) injury; (c) injury stabilized with Dynesys at L3-L4 (standard spacer); (d) long spacer (+2 mm); and (e) short spacer (-2 mm). Intervertebral rotations were measured using an optoelectronic camera system. The intersegmental range of motion (ROM), neutral zone (NZ), and three-dimensional helical axis of motion (HAM) were calculated. Statistical significance of changes in ROM, NZ, and HAM was determined using repeated measures analysis of variance (ANOVA) and Student-Newman-Keuls post-hoc analysis with P<0.05. Implantation of the standard length Dynesys significantly reduced ROM compared to the intact and injured specimens, with the least significant changes seen in axial rotation. Injury typically increased the NZ, but implantation of the Dynesys restored the NZ to a magnitude less that that of the intact spine. The Dynesys produced a significant posterior shift in the HAM in flexion-extension and axial rotation. The spacer length had a significant effect on ROM with the long spacer resulting in the largest ROM in all loading directions without a follower preload. The largest differences were in axial rotation. A 4 mm increase in spacer length led to an average intersegmental motion increase of 30% in axial rotation, 23% in extension, 14% in flexion, and 11% in lateral bending. There were no significant changes in NZ with different spacer lengths. Typically, the short spacer caused a greater shift and a greater change in orientation of the HAM than the long spacer. The long spacer resulted in a ROM and a motion pattern, as represented by the HAM, that was closer to that seen in an intact specimen. The results of this study suggest that the length of the Dynesys spacer altered the segmental position and therefore affected kinematic behaviour.

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The TFAS allowed considerable motion in all directions tested, with ROM being less than the intact in flexion and lateral bending, and greater than the intact in axial rotation. The helical axis of motion with the TFAS was not different from intact in flexion-extension and lateral bending, but it was shifted anteriorly in axial rotation. The kinematics of the TFAS were more similar to the intact spine than were the kinematics of the posterior fixation when applied to a destabilized lumbar spine.

A new bioactive bone cement without cytotoxic effect has been developed. Results show that minimally invasive techniques to apply this cement to porcine spines results in augmentation of mild burst fractures such that the original stiffness and strength of the vertebra are recovered. This new cement therefore shows potential as an augmentation to traditional instrumentation in the surgical management of vertebral fractures. The potential for further clinical applications is currently under investigation.

The ketone metabolite β-hydroxybutyrate (βOHB), is reported to be neuroprotective after spinal cord injury (SCI) in rats, but the underlying mechanism remains unknown. The present study aims to investigate effects of βOHB on suppression of oxidative stress and inhibition of class I histone deacetylases (HDACs) in in vivo and in vitro models. Rats were fed with ketogenic diet (KD) or standard diet (SD) for 3 weeks. A C5 hemi-contusion injury was applied to these animals on the 14th day of experiment, and spinal cord samples were harvested on the 1st, 3rd and 7th days after SCI, respectively. The blood ketone levels were significantly higher in the KD groups. KD reduced oxidative stress markers and reactive oxygen species (ROS) products, downregulated the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX)2 and NOX4, and upregulated the expression of forkhead box group O (FOXO)3a, mitochondrial superoxide dismutase (MnSOD), and catalase after SCI. The in vitro study, performed on PC12 cells, indicated that βOHB inhibited HO-induced ROS production, decreased NOX2 and NOX4 protein levels, and upregulated FOXO3a, MnSOD, and catalase levels in a dose-dependent manner, which was consistent with the in vivo results. The ketone metabolite βOHB inhibited HDAC1, HDAC2, and HDAC3 activity, but not HDAC8 in SCI rats and PC12 cells. Depletion of HDAC1 or HDAC2 with small interfering RNA (siRNA) attenuated HO-induced ROS production and protein carbonylation and elevated FOXO3a protein levels, meanwhile reducing NOX2 and NOX4 protein expression in PC12 cells. Our results indicate that the ketone metabolite βOHB attenuates oxidative stress in SCI by inhibition of class I HDACs, and selected suppression of HDAC1 or HDAC2 regulates FOXO3a, NOX2, and NOX4 expression. Therefore, the ketone metabolite βOHB may be a novel promising therapeutic agent for SCI.

The dynamic plate appeared to provide better stabilization in extension, and the technique of endplate preparation has some effect on immediate stabilization, dependent on the type of plate employed. Bone mineral density of the specimen was a strong determinant of the degree of stabilization achieved, regardless of the type of plate used.

Implantation of the Dynesys did not affect peak facet contact forces in extension or axial rotation compared with an intact specimen, but did alter these loads in flexion and lateral bending. The spacer length affected the compression of the posterior elements, with a shorter spacer typically producing greater facets loads than a longer one.

This study quantified the volumetric bone mineral density variations within the S1 body and ala, and a significant linear correlation between the screw insertion torque and bone mineral density was found. Optimal sacral screw insertion pathways were also outlined based on bone mineral density values.