A damaged vertebral body can exhibit accelerated ‘creep’ under constant load, leading to progressive vertebral deformity. However, the risk of this happening is not easy to predict in clinical practice. The present cadaveric study aimed to identify morphometric measurements in a damaged vertebral body that can predict a susceptibility to accelerated creep. Mechanical testing of 28 human spinal motion segments (three vertebrae and intervening soft tissues) showed how the rate of creep of a damaged vertebral body increases with increasing “damage intensity” in its trabecular bone. Damage intensity was calculated from vertebral body residual strain following initial compressive overload. The calculations used additional data from 27 small samples of vertebral trabecular bone, which examined the relationship between trabecular bone damage intensity and residual strain.Abstract
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The study aim was to simulate oblique spinous process abutment (SPA) in cadaveric spines and determine how this affects coupled motion in the coronal plane. L4-S1 spinal segments from thirteen cadavers were loaded on a materials testing machine in pure compression at 1kN for 10 minutes. Reflective markers on the vertebral bodies were used to assess coronal motion using a motion analysis system. Oblique SPA was simulated by attaching moulded oblique aluminium strips to the L4 and L5 spinous processes. In each specimen, both a right- and left-sided SPA was simulated, in random order, and compression at 1kN was again applied. All tests were then repeated after endplate fracture. Coronal plane motion at baseline was compared with values following simulated SPA using Mann Whitney U-tests. Pre-fracture, SPA increased coronal motion by 0.28° and 0.34° on right and left sides respectively, compared to baseline, only the former was significant (P=0.03). Post-fracture, SPA decreased coronal motion by 0.36° and 0.46° on right and left sides respectively, only the latter was significant (P=0.03). Simulated oblique SPA in the intact spine initiated an increase in coronal motion during pure axial loading. These findings provide limited evidence that oblique SPA may be causative in DLS.
To determine if patients with coronal plane deformity in the lumbar spine have a higher grade of lumbar spine subtype compared to controls. This was a retrospective case/control study based on a review of radiological investigations in 250 patients aged over 40 years who had standing plain film lumbar radiographs with hips present. Measurements of lumbar coronal plane angle, lumbar lordosis, sacral slope, pelvic tilt and pelvic incidence were obtained. “Cases” with degenerative scoliosis (n=125) were defined as patients with a lumbar coronal plane angle of >10°. Lumbar spine subtype was categorised (1–4) using the Roussouly classification. Lumbar spine subtype was dichotomised into low (type 1,2) or high (type 3,4). Prevalence of lumbar spine subtype in cases versus controls was compared using the Chi squared test. Pelvic incidence was compared using an unpaired T-test. Predictors of lumbar coronal plane angle were identified using stepwise multiple regression. Significance was accepted at P<0.05.Aim:
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Herniated disc tissue removed at surgery is mostly nucleus pulposus, with varying proportions of annulus fibrosus, cartilage endplate, and bone. Herniated nucleus swells and loses proteoglycans, and herniated annulus is invaded by blood vessels and inflammatory cells. However, little is known about the significance of endplate cartilage and bone within a herniation. Herniated tissue was removed surgically from 21 patients (10 with sciatica, 11 without). 5-μm sections were examined using H&E, Toluidine blue, Giemsa, and Masson-trichrome stains. Each tissue type in each specimen was scored for tears/fissures, neovascularisation, proteoglycan loss, cell clustering, and inflammatory cell invasion. Proportions of each tissue type were quantified using image analysis software.Introduction
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Disc degeneration is often scored using macroscopic and microscopic scoring systems. Although reproducible, these scores may not accurately reflect declining function in a degenerated disc. Accordingly, we compared macroscopic and microscopic degeneration scores with measurements of disc function. Thirteen cadaveric motion segments (62–93 yrs) were compressed to 1kN while a pressure-transducer was pulled across the mid-sagittal diameter of the disc. Resulting stress profiles indicated intradiscal pressure (IDP), and maximum stress in the anterior (MaxStress_Ant) and posterior (MaxStress_Post) annulus. Macroscopic Introduction
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Physical disruption of the extracellular matrix influences the mechanical and chemical environment of intervertebral disc cells. We hypothesise that this can explain degenerative changes such as focal proteoglycan loss, impaired cell-matrix binding, cell clustering, and increased activity of matrix-degrading enzymes. Disc tissue samples were removed surgically from 11 patients (aged 34–75 yrs) who had a painful but non-herniated disc. Each sample was divided into a pair of specimens (approximately 5mm3), which were cultured at 37°C under 5% CO2. One of each pair was allowed to swell, while the other was restrained by a perspex ring. Live-cell imaging was performed with a wide field microscope for 36 hrs. Specimens were then sectioned at 5 and 30 μm for histology and immunofluorescence using a confocal microscope. Antibodies were used to recognise free integrin receptor α5β1, matrix metalloprotease MMP-1, and denatured collagen types I-III. Proteoglycan content of the medium, analysed using the colorimetric DMMB assay, was used to assess tissue swelling and GAG loss. Constrained/unconstrained results were compared using matched-pair t-tests.Introduction
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Decreasing endplate porosity has been proposed as a risk factor for intervertebral disc degeneration, because it interferes with disc metabolite transport. However, endplate porosity has recently been shown to Nineteen cadaver motion segments (61–98 yrs) were compressed to 1kN while a pressure-transducer was pulled across the mid-sagittal diameter of the disc. Stress profiles indicated nucleus (intradiscal) pressure (IDP) and maximum stress in the anterior and posterior annulus. Subsequently, micro-CT was used to evaluate endplate porosity along the antero-posterior diameter of the adjacent endplates. Data were analysed using ANOVA and linear regression.Introduction
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Discogenic pain is associated with ingrowth of blood vessels and nerves, but uncertainty over the extent of ingrowth is hindering development of appropriate treatments. We hypothesise that adult human annulus fibrosus is such a dense crosslinked tissue that ingrowth Disc tissue was examined from 61 patients (aged 37–75 yrs) undergoing surgery for disc herniation, degeneration or scoliosis. 5 µm sections were stained with H&E to identify structures and tissue types. 30 µm frozen sections were examined using confocal microscopy, following immunostaining for CD31 (an endothelial cell marker), PGP 9.5 and Substance P (general and nociceptive nerve markers, respectively). Fluorescent tags were attached to the antibodies. ‘Volocity’ software was used to calculate numbers and total cross-sectional area of labelled structures, and to measure their distance from the nearest free surface (disc periphery, or annulus fissure).Introduction
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Senile kyphosis arises from anterior ‘wedge’ deformity of thoracolumbar vertebrae, often in the absence of trauma. It is difficult to reproduce these deformities in cadaveric spines, because a vertebral endplate usually fails first. We hypothesise that endplate fracture concentrates sufficient loading on to the anterior cortex that a wedge deformity develops subsequently under physiological repetitive loading. Thirty-four cadaveric thoracolumbar “motion segments,” aged 70–97 yrs, were overloaded in combined bending and compression. Physiologically-reasonable cyclic loading was then applied, at progressively higher loads, for up to 2 hrs. Before and after fracture, and again after cyclic loading the Introduction
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Osteoporotic vertebral fractures can cause severe vertebral wedging and kyphotic deformity. This study tested the hypothesis that kyphoplasty restores vertebral height, shape and mechanical function to a greater extent than vertebroplasty following severe wedge fractures. Pairs of thoracolumbar “motion segments” from seventeen cadavers (70–97 yrs) were compressed to failure in moderate flexion and then cyclically loaded to create severe wedge deformity. One of each pair underwent vertebroplasty and the other kyphoplasty. Specimens were then creep loaded at 1.0kN for 1 hour. At each stage of the experiment the following parameters were measured: vertebral height and wedge angle from radiographs, motion segment compressive stiffness, and stress distributions within the intervertebral discs. The latter indicated intra-discal pressure (IDP) and neural arch load-bearing (FN).Introduction
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Herniated disc tissue removed at surgery usually appears degenerated, and MRI often reveals degenerative changes in adjacent discs and vertebrae. This has fostered the belief that a disc Surgically-removed discs were examined using histology, immunohistochemistry and confocal microscopy. 21 samples of herniated tissues were compared with age-matched tissues excised from 11 patients whose discs had reached a similar Pfirrman grade of degeneration but without herniating. Degenerative changes were assessed separately in three tissue types (where present): nucleus, inner annulus, and outer annulus. Mann-Whitney U tests were used to compare ‘herniated’ vs ‘in-situ’ tissues.Introduction
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Senile kyphosis arises from anterior ‘wedge’ deformity of thoracolumbar vertebrae, often in the absence of trauma. It is difficult to reproduce these deformities in cadaveric spines, because a vertebral endplate usually fails first. We hypothesise that endplate fracture concentrates sufficient loading on to the anterior cortex that a wedge deformity develops subsequently under physiological repetitive loading. Thirty-four cadaveric thoracolumbar “motion segments,” aged 70–97 yrs, were overloaded in combined bending and compression. Physiologically-reasonable cyclic loading was then applied, at progressively higher loads, for up to 2 hrs. Before and after fracture, and again after cyclic loading the distribution of compressive loading on the vertebral body was assessed from recordings of compressive stress along the sagittal mid-plane of the adjacent intervertebral disc. Vertebral deformity was assessed from radiographs at the beginning and end of testing.Introduction
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Vertebroplasty helps to restore mechanical function to a fractured vertebra. We investigated how the Nine pairs of three-vertebra cadaver spine specimens (aged 67–90 yr) were compressed to induce fracture. One of each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Specimens were then creep-loaded at 1.0kN for 1hr. Before and after vertebroplasty, compressive stiffness was determined, and stress profilometry was performed by pulling a pressure-transducer through each disc whilst under 1.0kN load. Profiles indicated intradiscal pressure (IDP) and compressive load-bearing by the neural arch (FN) at both disc levels. Micro-CT was used to quantify cement fill in the anterior and posterior halves of each augmented vertebral body, and also in the region immediately adjacent to the fractured endplateIntroduction
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Risk factors for disc degeneration depend on how the condition is defined, i.e. on the specific disc degeneration “phenotype”. We present evidence that there are two major and largely-distinct types of disc degeneration. The relevant research literature was reviewed and re-interpreted.Introduction
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Delamination of the annulus fibrosus is an early feature of disc degeneration, and it allows individual lamellae to collapse into the nucleus, or to bulge radially outwards. We 102 thoracolumbar motion segments (T8-9 to L5-S1) were dissected from 42 cadavers aged 19–92 yrs. Each specimen was subjected to 1 kN compression, while intradiscal compressive stresses were measured by pulling a pressure transducer along the disc's mid-sagittal diameter. Stress gradients were measured, in the anterior and posterior annulus, as the average rate of increase in compressive stress (MPa/mm) between the nucleus and the region of maximum stress in the annulus. Average nucleus pressure was also recorded. Disc degeneration was assessed macroscopically on a scale of 1–4.Introduction
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Severe ‘discogenic’ back pain may be related to the ingrowth of nerves and blood vessels, although this is controversial. We hypothesise that ingrowth is greater in painful discs, and is facilitated in the region of annulus fissures. We compared tissue removed at surgery from 22 patients with discogenic back pain and/or sciatica, and from 16 young patients with scoliosis who served as controls. Wax-embedded specimens were sectioned at 7μm. Nerves and blood vessels were identified using histological stains, and antibodies to PGP 9.5 and CD31 respectively.Introduction
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Fracture of an osteoporotic vertebral body reduces vertebral stiffness and decompresses the nucleus in the adjacent intervertebral disc. This leads to high compressive stresses acting on the annulus and neural arch. Altered load-sharing at the fractured level may influence loading of neighbouring vertebrae, increasing the risk of a fracture ‘cascade’. Vertebroplasty has been shown to normalise load-bearing by fractured vertebrae but it may increase the risk of adjacent level fracture. The aim of this study was to determine the effects of fracture and subsequent vertebroplasty on the loading of neighbouring (non-augmented) vertebrae. Fourteen pairs of three-vertebra cadaver spine specimens (67-92 yr) were loaded to induce fracture. One of each pair underwent vertebroplasty with PMMA, the other with a resin (Cortoss). Specimens were then creep loaded at 1.0kN for 1hr. In 17 specimens where the upper or lower vertebra fractured, compressive stress distributions were measured in the disc between adjacent non-fractured vertebrae by pulling a pressure transducer through the disc whilst under 1.0kN load. These ‘stress profiles’ were obtained at each stage of the experiment (in flexion and extension) in order to quantify intradiscal pressure (IDP), the size of stress concentrations in the posterior annulus (SP) and compressive load-bearing by anterior (FA) and posterior (FP) halves of the vertebral body and by the neural arch (FN).Background
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In the annulus fibrosus of degenerated intervertebral discs, disruption to inter-lamellar cross-ties appears to lead to delamination, and the development of anulus fissures. We hypothesise that such internal disruption is likely to be driven by high gradients of compressive stress (i.e. large differences in stress from the nucleus to the mid anulus). Eighty-nine thoracolumbar motion segements, from T7/8 to L4/5, were dissected from 38 cadavers aged 42-96 yrs. Each was subjected to 1 kN compressive loading, while intradiscal compressive stresses were measured by pulling a pressure transducer along the disc's mid-sagittal diameter. Measurements were repeated in flexed and extended postures. Stress gradients were measured, in the anterior and posterior anulus of each disc, as the average rate of increase in stress (MPa/mm) between the nucleus and the region of maximum compressive stress in the anulus. Average nucleus pressure (IDP) was also recorded.Background
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Vertebral osteoporotic fracture increases both elastic and time-dependent ('creep') deformations of the fractured vertebral body during subsequent loading. The accelerated rate of creep deformation is especially marked in central and anterior regions of the vertebral body where bone mineral density is lowest. In life, subsequent loading of damaged vertebrae may cause anterior wedging of the vertebral body which could contribute to the development of kyphotic deformity. The aim of this study was to determine whether gradual creep deformations of damaged vertebrae can be reduced by vertebroplasty. Fourteen pairs of spine specimens, each comprising three vertebrae and the intervening soft tissue, were obtained from cadavers aged 67-92 yr. Specimens were loaded in combined bending and compression until one of the vertebral bodies was damaged. Damaged vertebrae were then augmented so that one of each pair underwent vertebroplasty with polymethylmethacrylate cement, the other with a resin (Cortoss). A 1kN compressive force was applied for 1 hr before fracture, after fracture, and after vertebroplasty, while creep deformation was measured in anterior, middle and posterior regions of each vertebral body, using a MacReflex optical tracking system.Introduction
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The Plantaris Longus Tendon (PLT) may be implicated in Achilles (AT) tendinopathy. Different mechanical characteristics may be the cause. This study is designed to measure these. Six PLT and six AT were harvested from frozen cadavers (aged 65-88). Samples were stretched to failure using a Minimat 2000(tm) (Rheometric Scientific Inc.). Force and elongation were recorded. Calculated tangent stiffness, failure stress and strain were obtained. Averaged mechanical properties were compared using paired, one-tailed t-tests.Background
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