A database of lumbar spinal mechanical behavior for validation of spinal analytical models.

Data from two experimental studies with eight specimens each of spinal motion segments and/or intervertebral discs are presented in a form that can be used for comparison with finite element model predictions. The data include the effect of compressive preload (0, 250 and 500N) with quasistatic cyclic loading (0.0115Hz) and the effect of loading frequency (1, 0.

Metabolic Effects of Angulation, Compression, and Reduced Mobility on Annulus Fibrosis in a Model of Altered Mechanical Environment in Scoliosis.

Study Design: Comparison of disc tissue from rat tails in 6 groups with different mechanical conditions imposed.

Objectives: To identify disc annulus changes associated with the supposed altered biomechanical environment in a spine with scoliosis deformity using an immature rat model that produces disc narrowing and wedging.

Background: Intervertebral discs become wedged and narrowed in a scoliosis curve, probably partly because of an altered biomechanical environment.

Contributions of Remodeling and Asymmetrical Growth to Vertebral Wedging in a Scoliosis Model.

Study Design: We performed a laboratory study of rats of 3 different ages with imposed angulation and compressive loading to caudal vertebrae to determine causes of vertebral wedging.

Objectives: The purpose was to determine the percentage of total vertebral wedging that was caused by asymmetric growth, vertebral body, and epiphyseal wedging. Approval from the Institutional Animal Care and Use Committee, the University of Vermont, was obtained for the live animal procedures used in this study.

Intervertebral disc changes with angulation, compression and reduced mobility simulating altered mechanical environment in scoliosis.

Purpose: The intervertebral discs become wedged and narrowed in scoliosis, and this may result from altered biomechanical environment. The effects of four permutations of disc compression, angulation and reduced mobility were studied to identify possible causes of progressive disc deformity in scoliosis. The purpose of this study was to document morphological and biomechanical changes in four different models of altered mechanical environment in intervertebral discs of growing rats and in a sham and control groups.

Abdominal muscle activation increases lumbar spinal stability: analysis of contributions of different muscle groups.

Background: Antagonistic activation of abdominal muscles and increased intra-abdominal pressure are associated with both spinal unloading and spinal stabilization. Rehabilitation regimens have been proposed to improve spinal stability via selective recruitment of certain trunk muscle groups. This biomechanical analytical study addressed whether lumbar spinal stability is increased by such selective activation.

Nonfusion treatment of adolescent idiopathic scoliosis by growth modulation and remodeling.

Background: Adolescent idiopathic scoliosis (AIS) is a common disorder in which the spine gradually develops a curvature that is first detected in patients between 11 and 17 years of age. The only accepted treatment methods are bracing and surgery. Whether brace treatment alters the natural history is being questioned, and patient compliance is low.

Refinement of elastic, poroelastic, and osmotic tissue properties of intervertebral disks to analyze behavior in compression.

Intervertebral disks support compressive forces because of their elastic stiffness as well as the fluid pressures resulting from poroelasticity and the osmotic (swelling) effects. Analytical methods can quantify the relative contributions, but only if correct material properties are used. To identify appropriate tissue properties, an experimental study and finite element analytical simulation of poroelastic and osmotic behavior of intervertebral disks were combined to refine published values of disk and endplate properties to optimize model fit to experimental data.

Intra-abdominal pressure and abdominal wall muscular function: Spinal unloading mechanism.

Background: The roles of antagonistic activation of abdominal muscles and of intra-abdominal pressurization remain enigmatic, but are thought to be associated with both spinal unloading and spinal stabilization in activities such as lifting. Biomechanical analyses are needed to understand the function of intra-abdominal pressurization because of the anatomical and physiological complexity, but prior analyses have been over-simplified.

Methods: To test whether increased intra-abdominal pressure was associated with reduced spinal compression forces for efforts that generated moments about each of the principal axis directions, a previously published biomechanical model of the spine and its musculature was modified by the addition of anatomically realistic three-layers of curved abdominal musculature connected by fascia to the spine.

The central hip vertical axis: a reference axis for the Scoliosis Research Society three-dimensional classification of idiopathic scoliosis.

Study Design: Reliability comparison of 2 radiographic axis systems by inter- and intraobserver variability.

Objective: To determine whether the central hip vertical axis (CHVA) provides a more reliable reference axis for the evaluation of scoliosis.

Summary Of Background Data: Current practices in the evaluation of the scoliotic spine use the central sacral vertical line (CSVL), a true vertical drawn upward from the middle of S1, to assess the spinal deformity.

Interobserver and intraobserver variability in the identification of the Lenke classification lumbar modifier in adolescent idiopathic scoliosis.

Study Design: Interobserver and intraobserver reliability study for the identification of the Lenke classification lumbar modifier by a panel of experts compared with a computer algorithm.

Objectives: To measure the variability of the Lenke classification lumbar modifier and determine if computer assistance using 3-dimensional spine models can improve the reliability of classification.

Summary Of Background Data: The lumbar modifier has been proposed to subclassify Lenke scoliotic curve types into A, B, and C on the basis of the relationship between the central sacral vertical line (CSVL) and the apical lumbar vertebra.

Growth plate mechanics and mechanobiology. A survey of present understanding.

The longitudinal growth of long bones occurs in growth plates where chondrocytes synthesize cartilage that is subsequently ossified. Altered growth and subsequent deformity resulting from abnormal mechanical loading is often referred to as mechanical modulation of bone growth. This phenomenon has key implications in the progression of infant and juvenile musculoskeletal deformities, such as adolescent idiopathic scoliosis, hyperkyphosis, genu varus/valgus and tibia vara/valga, as well as neuromuscular diseases.

Classification of scoliosis deformity three-dimensional spinal shape by cluster analysis.

Study Design: Cluster analysis of existing database of spinal shape of patients attending a scoliosis clinic.

Objective: To determine whether patients with scoliosis can be classified into distinct groups by 3-dimensional curve shape.

Summary Of Background Data: Subjective or semiquantitative methods can be used to classify curve types in scoliosis, with the goal of rationalizing surgical planning.

Spatially resolved streaming potentials of human intervertebral disk motion segments under dynamic axial compression.

Intervertebral disk degeneration results in alterations in the mechanical, chemical, and electrical properties of the disk tissue. The purpose of this study is to record spatially resolved streaming potential measurements across intervertebral disks exposed to cyclic compressive loading. We hypothesize that the streaming potential profile across the disk will vary with radial position and frequency and is proportional to applied load amplitude, according to the presumed fluid-solid relative velocity and measured glycosaminoglycan content.

Three-dimensional classification of thoracic scoliotic curves.

Study Design: Three-dimensional (3D) characterization of the thoracic scoliotic spine (cross-sectional study).

Objectives: To investigate the presence of subgroups within Lenke type-1 curves by evaluating the thoracic segment indices extracted from 3D reconstructions of the spine, and to propose a new clinically relevant means (the daVinci representation) to report 3D spinal deformities.

Summary Of Background Data: Although scoliosis is recognized to be a 3D deformity of the spine its measurement and classification have predominantly been based on radiographs which are 2D projections in the coronal and sagittal planes.

Mechanical modulation of spinal growth and progression of adolescent scoliosis.

It is unclear why some children with a small magnitude scoliosis at the onset of the adolescent growth spurt develop a progressive curve. Normally the skeleton grows symmetrically, presumably because genetic and epigenetic factors regulating growth to maintain growth symmetry despite activities and environmental factors causing asymmetrical loading of the spine. This chapter reviews the recently published data relating to the notion that progression of scoliosis is a result of biomechanical factors modulating spinal growth ('vicious cycle' theory).

Different effects of static versus cyclic compressive loading on rat intervertebral disc height and water loss in vitro.

Study Design: In vitro biomechanical study on rat caudal motion segments to evaluate association between compressive loading and water content under static and cyclic conditions.

Objective: To test hypotheses: 1) there is no difference in height loss and fluid (volume) loss of discs loaded in compression under cyclic (0.15-1.

Analysis and simulation of progressive adolescent scoliosis by biomechanical growth modulation.

Scoliosis is thought to progress during growth because spinal deformity produces asymmetrical spinal loading, generating asymmetrical growth, etc. in a 'vicious cycle.' The aim of this study was to test quantitatively whether calculated loading asymmetry of a spine with scoliosis, together with measured bone growth sensitivity to altered compression, can explain the observed rate of scoliosis progression in the coronal plane during adolescent growth.

Measurements of proteoglycan and water content distribution in human lumbar intervertebral discs.

Study Design: Study of regional variations in composition in a sample of 9 mildly to moderately degenerated human intervertebral discs.

Objective: The aim of this study was to obtain proteoglycan distribution in human lumbar discs with high position resolution in the: 1) sagittal, 2) coronal, and 3) axial directions.

Summary Of Background Data: Regional variation in disc proteoglycan content has only been reported in coronal sections in a small number of discs and with low spatial resolution in the sagittal direction, and has not been reported in the axial direction.

Alterations in the growth plate associated with growth modulation by sustained compression or distraction.

Sustained mechanical load is known to modulate endochondral growth in the immature skeleton, but it is not known what causes this mechanical sensitivity. This study aimed to quantify alterations in parameters of growth plate performance associated with mechanically altered growth rate. Vertebral and proximal tibial growth plates of immature rats and cattle, and rabbit (proximal tibia only) were subjected to different magnitudes of sustained loading, which altered growth rates by up to 53%.

Intervertebral disc adaptation to wedging deformation.

Unlabelled: Although scoliosis includes wedge deformities of both vertebrae and discs, little is known about the causes of the discal changes, and whether they result from mechanical influences on growth and/or remodelling.

Methods And Materials: An external apparatus attached to transvertebral pins applied compression and 15 degrees of angulation to each of two adjacent young rat caudal intervertebral discs for 5 weeks (four animals), or for 10 weeks (four animals). Each week, micro-CT scanning documented the in vivo discal wedging.

Biomechanical spinal growth modulation and progressive adolescent scoliosis--a test of the 'vicious cycle' pathogenetic hypothesis: summary of an electronic focus group debate of the IBSE.

There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an on-line Delphi discussion.

Vertebral height growth predominates over intervertebral disc height growth in adolescents with scoliosis.

Study Design: A cross-sectional study of spinal stereoradiographs of adolescents with scoliosis to measure growth.

Objective: To determine the relative contributions of the vertebral bodies and intervertebral discs to the increase in spinal length between T5 and L5, over the age range of 7.5-20 years.

Endochondral growth in growth plates of three species at two anatomical locations modulated by mechanical compression and tension.

Sustained mechanical loading alters longitudinal growth of bones, and this growth sensitivity to load has been implicated in progression of skeletal deformities during growth. The objective of this study was to quantify the relationship between altered growth and different magnitudes of sustained altered stress in a diverse set of nonhuman growth plates. The sensitivity of endochondral growth to differing magnitudes of sustained compression or distraction stress was measured in growth plates of three species of immature animals (rats, rabbits, calves) at two anatomical locations (caudal vertebra and proximal tibia) with two different ages of rats and rabbits.

Computer-assisted algorithms improve reliability of King classification and Cobb angle measurement of scoliosis.

Study Design: Interobserver and intraobserver reliability study of improved method to evaluate radiographs of patients with scoliosis.

Objective: To determine the reliability of a computer-assisted measurement protocol for evaluating Cobb angle and King et al classification.

Summary Of Background Data: Evaluation of scoliosis radiographs is inherently unreliable because of technical and human judgmental errors.