Michael F. Keane

Fill of the Nucleus Cavity Affects Mechanical Stability in Compression, Bending, and Torsion of a Spine Segment, Which Has Undergone Nucleus Replacement

Study Design. Axial loading, rotation, and bending were applied to human cadaveric lumbar segments to investigate the changes in disc mechanics with denucleation and incremental delivery of a novel hydrogel nucleus replacement. Objective. The purpose of this study was to investigate the effect of nucleus implant injection pressure/volume relationships on the quasi-static mechanical behavior of the human cadaveric lumbar intervertebral disc to determine if intact biomechanics could be reproduced with nucleus-implanted discs. Summary of Background Data. Previous studies have shown that volumetric filling of the nucleus cavity with a compliant nucleus replacement device will affect compressive stiffness of the implanted intervertebral disc, but data regarding restoration of mechanics through cavity pressurization are lacking. Methods. A total of 12 intact lumbar anterior column units were loaded in series in axial loading, axial rotation, lateral bending, and flexion/extension (FE). Each segment was fully denucleated and implanted with a hydrogel nucleus replacement using pressurization between 12 psi and 40 psi. Range of motion (ROM), neutral zone (NZ), energy dissipation (HYS), disc height (DH), and stiffness were compared among the intact, denucleated, and implanted conditions. Results. Denucleation significantly destabilized the segments compared to intact controls as shown by increased ROM, NZ, and HYS, and decreased DH and stiffness through the NZ. As the nucleus cavity was repressurized with increasing volumes of hydrogel implant, the segments were stabilized and DH was restored to the intact level. No significant differences from intact were observed in any loading direction for ROM, NZ, or DH after the segments were implanted with the nucleus replacement device using inflation pressures between 20 psi and 40 psi. Conclusion. Compliant nucleus replacement using inflation pressures of 20 to 40 psi resulted in restoration of intact mechanics. Mechanical function was dependent on the volume of implant injected into the nucleus cavity.

A novel hydrogel-coated polyester mesh prevents postsurgical adhesions in a rat model.

BACKGROUND The specific aim of this study was to determine the whether a novel, hydrogel-coated polyester mesh (Scout) can be used to reduce the incidence and severity of adhesion formation in vivo. METHODS An established rat model of post-surgical adhesion formation was used in which adhesions are generated through surgical trauma to the surfaces of the cecum and the adjacent abdominal wall. Thirty-seven rats were randomly allocated either to a control group (no intervention; n=14 rats) or to one of two treatment groups in which the abraded surfaces were separated with either the Scout material (n=11 rats) or an FDA-approved form of expanded polytetrafluorethylene (PTFE) (PRECLUDE Vessel Guard; n=12 rats). Animals were euthanized 7 d after surgery and gross necropsy examinations were performed. Mechanical testing was used to measure the strength of any adhesions that were identified, and histology was used to characterize within the adhesion tissue and on the surface(s) of the barrier materials. RESULTS Five animals were excluded because of surgical failure (1 control; 2 PRECLUDE Vessel Guard; 2 Scout). Adhesions were seen in 10 of 13 control animals (77%). There were no adhesions in any of the animals treated with either PRECLUDE Vessel Guard or Scout material. Histology demonstrated mild cellular adhesion to both the PRECLUDE Vessel Guard and the Scout material. Although there was a sub-acute to chronic inflammatory response to the surgical trauma, there was no evidence of delamination, shearing, or degradation of either the Scout material or PRECLUDE Vessel Guard. CONCLUSIONS The hydrogel-coated Scout material was as effective as the approved predicate material in this model. Both materials were well tolerated. Further testing of the Scout material is now warranted.

Fill of the Nucleus Cavity Affects Mechanical Stability in Compression, Bending and Torsion of a Spine Segment Which Has Undergone Nucleus Replacement

Axial loading, rotation and bending were applied to human cadaveric lumbar segments to investigate changes in disc mechanics with denucleation and incremental delivery of a novel hydrogel nucleus replacement implant. Changes in disc height, range of motion, neutral zone, hysteresis and stiffness were examined.Copyright