Biomechanical Comparisons of Pull Out Strengths After Pedicle Screw Augmentation with Hydroxyapatite, Calcium Phosphate, or Polymethylmethacrylate in the Cadaveric Spine.

Objective: In vertebrae with low bone mineral densities pull out strength is often poor, thus various substances have been used to fill screw holes before screw placement for corrective spine surgery. We performed biomechanical cadaveric studies to compare nonaugmented pedicle screws versus hydroxyapatite, calcium phosphate, or polymethylmethacrylate augmented pedicle screws for screw tightening torques and pull out strengths in spine procedures requiring bone screw insertion.

Methods: Seven human cadaveric T10-L1 spines with 28 vertebral bodies were examined by x-ray to exclude bony abnormalities.

Biomechanical comparison of cervical fixation via transarticular facet screws without rods versus lateral mass screws with rods.

Objective: Transarticular facet screws restore biomechanical stability to the cervical spine when posterior cervical anatomy has been compromised. This study compares the more recent, less invasive, and briefer transarticular facet screw system without rods with the lateral mass screw system with rods.

Methods: For this study, 6 human cervical spines were obtained from cadavers.

Biomechanical analysis of disc pressure and facet contact force after simulated two-level cervical surgeries (fusion and arthroplasty) and hybrid surgery.

Objective: The objective of this study was designed to compare 2-level cervical disc surgery (2-level anterior cervical discectomy and fusion [ACDF] or disc arthroplasty) and hybrid surgery (ACDF/arthroplasty) in terms of postoperative adjacent-level intradiscal pressure (IDP) and facet contact force (FCF).

Methods: Twenty-four cadaveric cervical spines (C3-T2) were tested in various modes, including extension, flexion, and bilateral axial rotation, to compare adjacent-level IDP and FCF after specified treatments as follows: 1) C5-C6 arthroplasty using ProDisc-C (Synthes Spine, West Chester, Pennsylvania, USA) and C6-C7 ACDF, 2) C5-C6 ACDF and C6-C7 arthroplasty using ProDisc-C, 3) 2-level C5-C6/C6-C7 disc arthroplasties, and 4) 2-level C5-C6/C6-C7 ACDF. IDPs were recorded at anterior, central, and posterior disc portions.

Biomechanical evaluations of various c1-c2 posterior fixation techniques.

Study Design: A biomechanical in vitro study using human cadaveric spine.

Objective: To compare the biomechanical stability of pedicle screws versus various established posterior atlantoaxial fixations used to manage atlantoaxial instability.

Summary Of Background Data: Rigid screw fixation of the atlantoaxial complex provides immediate stability and excellent fusion success though has a high risk of neurovascular complications.

Biomechanical analysis of Goel technique for C1-2 fusion.

Object: The Goel technique, in which C1-2 intraarticular spacers are used, may be performed to restore stability to a disrupted atlantoaxial complex in conjunction with the Harms technique of placing polyaxial screws and bilateral rods. However, it has yet to be determined biomechanically whether the addition of the C1-2 joint spacers increases the multiaxial rigidity of the fixation construct. The goal of this study was to quantify changes in multiaxial rigidity of the combined Goel-Harms technique with the addition of C1-2 intraarticular spacers.

Biomechanical comparison of single-level posterior versus transforaminal lumbar interbody fusions with bilateral pedicle screw fixation: segmental stability and the effects on adjacent motion segments.

Object: Both posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) have been frequently undertaken for lumbar arthrodesis. These procedures use different approaches and cage designs, each of which could affect spine stability, even after the addition of posterior pedicle screw fixation. The objectives of this biomechanical study were to compare PLIF and TLIF, each accompanied by bilateral pedicle screw fixation, with regard to the stability of the fused and adjacent segments.

A biomechanical study of the instrumented and adjacent lumbar levels after In-Space interspinous spacer insertion.

Object: Interspinous process implants are becoming more common for the treatment of lumber disc degeneration. The authors undertook this study to evaluate the effect of the In-Space interspinous spacer on the biomechanics of the lumbosacral spine.

Methods: Seven L2-S1 cadaver spines were physiologically loaded in extension, flexion, lateral bending, and axial rotation modes.

Biomechanical analysis of the range of motion after placement of a two-level cervical ProDisc-C versus hybrid construct.

Study Design: The study design was that of an in vitro human cadaveric biomechanical analysis.

Objectives: The objective of this study was the biomechanical analysis of the range of motion (ROM) of a 2-level intact spine control versus total, then operative- and adjacent-segment ROM after (1) 2-level ProDisc-C placement (PP), (2) anterior cervical discectomy and fusions (ACDFs), and (3) hybrid constructs of both. Follower load and multidirectional testing were performed in each instance.

The Changes in Range of Motion after a Lumbar Spinal Arthroplasty with Charité in the Human Cadaveric Spine under Physiologic Compressive Follower Preload : A Comparative Study between Load Control Protocol and Hybrid Protocol.

Objective: To compare two testing protocols for evaluating range of motion (ROM) changes in the preloaded cadaveric spines implanted with a mobile core type Charité lumbar artificial disc.

Methods: Using five human cadaveric lumbosacral spines (L2-S2), baseline ROMs were measured with a bending moment of 8 Nm for all motion modes (flexion/extension, lateral bending, and axial rotation) in intact spine. The ROM was tracked using a video-based motion-capturing system.

Biomechanical evaluation of an interspinous stabilizing device, Locker.

Study Design: A biomechanical study.

Objective: To evaluate the biomechanical properties of a novel dynamic interspinous device named Locke

Summary Of Background Data: There has been no biomechanical study on this device.

Methods: Five human cadaveric lumbar spine specimens (L2-S1) were tested in the following sequence: (1) intact state; (2) after removal of the interspinous ligaments of L3-L4; (3) after application of the Locker at the interspinous space; (4) after destabilization of the L3-L4 motion segments; and (5) after reapplication of the Locker to the destabilized segments.

Range of motion change after cervical arthroplasty with ProDisc-C and prestige artificial discs compared with anterior cervical discectomy and fusion.

Object: Range of motion (ROM) changes were evaluated at the surgically treated and adjacent segments in cadaveric specimens treated with two different cervical artificial discs compared with those measured in intact spine and fusion models.

Methods: Eighteen cadaveric human cervical spines were tested in the intact state for the different modes of motion (extension, flexion, lateral bending, and axial rotation) up to 2 Nm. Three groups of specimens (fitted with either the ProDisc-C or Prestige II cervical artificial disc or submitted to anterior cervical discectomy and fusion [ACDF]) were tested after implantation at C6-7 level.

Changes in adjacent-level disc pressure and facet joint force after cervical arthroplasty compared with cervical discectomy and fusion.

Object: The authors of previous in vitro investigations have reported an increase in adjacent-level intradiscal pressures (IDPs) and facet joint stresses following cervical spine fusion. This study was performed to compare adjacent-level IDPs and facet force following arthroplasty with the fusion model.

Methods: Eighteen human cadaveric cervical spines were tested in the intact state for different modes of motion (extension, flexion, bending, and rotation) up to 2 Nm.

Biomechanical study of thoracolumbar junction fixation devices with different diameter dual-rod systems.

Object: Advances in the design of a smaller-diameter rod system for use in the thoracolumbar region prompted the authors to undertake this biomechanical study of two different thoracolumbar implants.

Methods: In vitro biomechanical testing was performed using human cadaveric spines. All specimens were loaded to a maximum moment of 5 Nm with 300-N axial preload in six modes of motion.

Comparison of the biomechanical stability of dense cancellous allograft with tricortical iliac autograft and fibular allograft for cervical interbody fusion.

Several choices are available for cervical interbody fusion after anterior cervical discectomy. A recent option is dense cancellous allograft (CS) which is characterized by an open-matrix structure that may promote vascularization and cellular penetration during early osseous integration. However, the biomechanical stability of CS should be comparable to that of the tricortical iliac autograft (AG) and fibular allograft (FA) to be an acceptable alternative to these materials.

Biomechanical comparison: stability of lateral-approach anterior lumbar interbody fusion and lateral fixation compared with anterior-approach anterior lumbar interbody fusion and posterior fixation in the lower lumbar spine.

Object: The stability of lateral lumbar interbody graft-augmented fusion and supplementary lateral plate fixation in human cadavers has not been determined. The purpose of this study was to investigate the immediate biomechanical stabilities of the following: 1) femoral ring allograft (FRA)-augmented anterior lumbar interbody fusion (ALIF) after left lateral discectomy combined with additional lateral MACS HMA plate and screw fixation; and 2) ALIF combined with posterior transpedicular fixation after anterior discectomy.

Methods: Sixteen human lumbosacral spines were loaded with six modes of motion.

A biomechanical comparison of three surgical approaches in bilateral subaxial cervical facet dislocation.

Object: In bilateral cervical facet dislocation, biomechanical stabilities between anterior locking screw/plate fixation after anterior cervical discectomy and fusion (ACDFP) and posterior transpedicular screw/rod fixation after anterior cervical discectomy and fusion (ACDFTP) have not been compared using the human cadaver, although ACDFP has been performed frequently. In this study the stability of ACDFP, a posterior wiring procedure after ACDFP (ACDFPW), and ACDFTP for treatment of bilateral cervical facet dislocation were compared.

Methods: Spines (C3-T1) from 10 human cadavers were tested in the intact state, and then after ACDFP, ACDFPW, and ACDFTP were performed.

A biomechanical comparison of supplementary posterior translaminar facet and transfacetopedicular screw fixation after anterior lumbar interbody fusion.

Object: Facet screw fixation is the lowest profile lumbar stabilization method. In this study the immediate biomechanical stability provided by the two different types of fixation are compared: translaminar facet screw (TLFS) and transfacetopedicular screw (TFPS) placement after anterior lumbar interbody fusion (ALIF) using a femoral ring allograft. Both facet screw fixation types were also compared with the gold standard, transpedicular screw and rod (TSR) fixation.

Biomechanical comparison of anterior and posterior stabilization methods in atlantoaxial instability.

Object: The authors compared the biomechanical stability of two anterior fixation procedures--anterior C1-2 Harms plate/screw (AHPS) fixation and the anterior C1-2 transarticular screw (ATS) fixation; and two posterior fixation procedures--the posterior C-1 lateral mass combined with C-2 pedicle screw/rod (PLM/APSR) fixation and the posterior C1-2 transarticular screw (PTS) fixation after destabilization.

Methods: Sixteen human cervical spine specimens (Oc-C3) were tested in three-dimensional flexion-extension, axial rotation, and lateral bending motions after destabilization by using an atlantoaxial C1-2 instability model. In each loading mode, moments were applied to a maximum of 1.