A cadaveric analysis of cervical fixation: the effect of intermediate fixation points and dynamization in multilevel cervical fusions.

Object: The authors conducted a study to compare biomechanical effects on the cervical spine of bridging fixation and intermediate fixation techniques, in both fixed and dynamic modes.

Methods: A biaxial, servohydraulic machine biomechanically tested 23 human cervical spines for stiffness and strain in compression, extension, flexion, and lateral bending through 3 specimen states: 1) intact, 2) defect (corpectomy and discectomy), and 3) grafting with plate application in 1 of 4 constructs: C3-7 dynamized long strut (DLS), C3-7 fixed long strut (FLS), C3-5-7 dynamized multisegment (DMS), and C3-5-7 fixed multisegment (FMS).

Results: Compared with FMS, FLS had significantly greater strain in extension (at C-3 and at the rostral and caudal parts of the graft) and in lateral bending (at C-3 and at the caudal part of the graft).

Incidence and outcome of graft resorption in anterior lumbar interbody fusion: using femoral ring allografts and recombinant human bone morphogenetic protein-2.

Study Design: Retrospective cohort.

Objective: To determine the incidence of resorption after anterior lumbar interbody fusion (ALIF) and its effect on outcome.

Summary Of Background Data: Recombinant human bone morphogenetic protein-2 (rhBMP-2) used in ALIF has been associated with a 0.

The difference in spine specimen dual-energy X-ray absorptiometry bone mineral density between in situ and in vitro scans.

Background Context: Human cadaveric specimens are commonly used to evaluate bone-implant interface strength in osteoporotic spine fixation. Dual-energy X-ray absorptiometry (DXA) scans are usually carried out on explanted spine specimens to measure bone mineral density (BMD) before in vitro biomechanical studies are carried out.

Purpose: The purposes of this study were to verify and quantify the difference in DXA BMD between unexplanted (in situ) and explanted (in vitro) scans and to develop and validate a correction factor (CF) between in vitro and in situ DXA BMD.

Biomechanical characteristics of hybrid hook-screw constructs in short-segment thoracic fixation.

Study Design: Ex vivo biomechanical testing of human cadaveric thoracic spine segments.

Objective: To determine whether a hybrid construct, using a combination of pedicle screws (PSs) and lamina hooks, was equivalent to a PS construct, in a short-segment thoracic spine fixation model.

Summary Of Background Data: Comparisons have been made among PS, lamina hook, and hybrid screw-hook constructs, but these have generally been in long-segment scoliosis correction.

Atlantoaxial fusion: a biomechanical analysis of two C1-C2 fusion techniques.

Background Context: Different atlantoaxial fusion techniques are used for instability. Transarticular screws are biomechanically superior to wiring techniques and equivalent to C1 lateral mass to C2 pedicle (C1LM-C2P) fixation. Recently, C1 lateral mass to C2 laminar (C1LM-C2L) fixation has been shown to have flexibility similar to C1LM-C2P fixation in flexion, extension, lateral bending, and axial rotation.

Biomechanical comparison of adjacent segmental motion after ventral cervical fixation with varying angles of lordosis.

Background Context: Complications, such as graft subsidence and adjacent segment degeneration, are not uncommon after ventral cervical fusion. It has been theorized, but not proven, that sagittal alignment may affect this process. It is therefore hypothesized that increasing lordosis during anterior cervical fusion decreases adjacent segment motion (ASM) and thus decreases the rate of adjacent disc degeneration.

Bone-mounted miniature robotic guidance for pedicle screw and translaminar facet screw placement: part 2--Evaluation of system accuracy.

Objective: To evaluate the accuracy of a novel bone-mounted miniature robotic system for percutaneous placement of pedicle and translaminar facet screws.

Methods: Thirty-five spinal levels in 10 cadavers were instrumented. Each cadaver's entire torso was scanned before the procedure.

Adjacent level load transfer following vertebral augmentation in the cadaveric spine.

Study Design: In vitro biomechanics.

Objective: To determine if osteoporotic vertebral compression fracture (VCF) augmentation increases adjacent level load transfer.

Summary Of Background Data: Osteoporotic VCF subsequent to augmentation may result from disease progression or increased adjacent level load transfer, or both.

Bone-mounted miniature robotic guidance for pedicle screw and translaminar facet screw placement: Part I--Technical development and a test case result.

Objective: To introduce a new miniature robot (SpineAssist; MAZOR Surgical Technologies, Caesarea, Israel) that has been developed and tested as a surgical assistant for accurate percutaneous placement of pedicle screws and translaminar facet screws.

Methods: Virtual projections in three planes-axial, lateral, and anteroposterior-are reconstructed for each vertebra from a preoperative computed tomographic (CT) scan. On a specially designed graphic user interface with proprietary software, the surgeon plans the trajectory of the screws.

The biomechanics of 1, 2, and 3 levels of vertebral augmentation with polymethylmethacrylate in multilevel spinal segments.

Study Design: Experimental biomechanics of multilevel segments with 0, 1, 2, and 3 vertebral levels of polymethylmethacrylate augmentation.

Objective: To compare multilevel spinal segments with different numbers (0, 1, 2, and 3) of vertebral levels augmented with polymethylmethacrylate.

Summary Of Background Data: The stiffness and strength of single-level polymethylmethacrylate augmentations in individual and multilevel vertebrae treated by kyphoplasty and vertebroplasty have been studied, but the biomechanics of multilevel segments with more than 1 vertebral level augmented with polymethylmethacrylate are lacking, yet this is clinically relevant in multilevel compression fracture treatment.

Biomechanical evaluation of the ventral and lateral surface shear strain distributions in central compared with dorsolateral placement of cages for lumbar interbody fusion.

Object: The purpose of this study was to measure and compare the ventral and lateral surface strain distributions and stiffness for two types of interbody cage placement: 1) central placement for anterior lumbar interbody fusion (ALIF); and 2) dorsolateral placement for extraforaminal lumbar interbody fusion (ELIF).

Methods: Two functional spine units were obtained for testing in each of 13 cadaveric spines, yielding 26 segments (three of which were not used because of bone abnormalities). Bilateral strain gauges were mounted adjacent to the endplate on the lateral and ventral walls of each vertebral body in the 23 motion segments.

The mechanics of polymethylmethacrylate augmentation.

Osteoporosis frequently leads to vertebral compression fractures. Percutaneous cement augmentation, one recent technique, may alter the biomechanics of the vertebral body and spinal segment. These alterations reportedly predispose the spinal segment to additional vertebral compression fractures.

Vertebroplasty and kyphoplasty: filler materials.

Over 700,000 osteoporotic compression fractures occur each year in the United States, twice the number of hip fractures. These vertebral fractures, most of which occur in the elderly, represent significant personal and societal burdens. Percutaneous vertebroplasty (PVP) is a minimally invasive method that involves the percutaneous injection of polymethylmethacrylate (PMMA) into a collapsed vertebral body to stabilize the vertebra.

Biomechanical comparison of transarticular facet screws to lateral mass plates in two-level instrumentations of the cervical spine.

Study Design: In vitro biomechanical comparison of transarticular facet screws to lateral mass plates in two level instrumentations of the cervical spine.

Objective: Lateral mass plates are costly, and screw placement is difficult. Facet screws have never been tested as an alternative in the cervical spine.

Histological evaluation of biopsies obtained from vertebral compression fractures: unsuspected myeloma and osteomalacia.

Study Design: A histological evaluation of biopsies obtained from presumed osteoporotic vertebral compression fractures (VCF) to confirm possible osteomalacia after tetracycline labeling.

Objective: To describe the results of a series of biopsies obtained at the time of vertebral augmentation in presumed osteoporotic VCF, with special reference to the presence of unmineralized bone (osteomalacia) and occult or unconfirmed plasma cell dyscrasia.

Summary Of Background Data: Vertebral augmentation is now widely performed as a method to treat osteoporotic or osteolytic VCF.

Biomechanical changes after the augmentation of experimental osteoporotic vertebral compression fractures in the cadaveric thoracic spine.

Background Context: Osteoporotic compression fractures are an important public health concern, leading to significant morbidity, mortality and economic burden. Cement augmentation procedures used to treat these fractures alter the biomechanics of the fractured segment, which could promote adjacent failure. However, if alignment is improved or restored, there will be less risk of adjacent failure.

Distribution of anterior cortical shear strain after a thoracic wedge compression fracture.

Background Context: Vertebral compression fractures (VCFs) are a common clinical problem and may follow trauma or be pathological. Osteoporosis increases susceptibility to fracture by reducing bone mass and weakening bone architecture. Approximately 2.