Vertebroplasty reduces progressive ׳creep' deformity of fractured vertebrae

Elderly vertebrae frequently develop an “anterior wedge” deformity as a result of fracture and creep mechanisms. Injecting cement into a damaged vertebral body (vertebroplasty) is known to help restore its shape and stiffness. We now hypothesise that vertebroplasty is also effective in reducing subsequent creep deformations. Twenty-eight spine specimens, comprising three complete vertebrae and the intervening discs, were obtained from cadavers aged 67–92 years. Each specimen was subjected to increasingly-severe compressive loading until one of its vertebrae was fractured, and the damaged vertebral body was then treated by vertebroplasty. Before and after fracture, and again after vertebroplasty, each specimen was subjected to a static compressive force of 1 kN for 1 h while elastic and creep deformations were measured in the anterior, middle and posterior regions of each adjacent vertebral body cortex, using a 2D MacReflex optical tracking system. After fracture, creep in the anterior and central regions of the vertebral body cortex increased from an average 4513 and 885 microstrains, respectively, to 54,107 and 34,378 microstrains (both increases: P<0.001). Elastic strains increased by a comparable amount. Vertebroplasty reduced creep in the anterior and central cortex by 61% (P=0.006) and 66% (P=0.017) respectively. Elastic strains were reduced by less than half this amount. Results suggest that the beneficial effects of vertebroplasty on the vertebral body continue long after the post-operative radiographs. Injected cement not only helps to restore vertebral shape and elastic properties, but also reduces subsequent creep deformation of the damaged vertebra

Intervertebral disc decompression following endplate damage: implications for disc degeneration depend on spinal level and age

Study Design. Mechanical and morphological studies on cadaveric spines. Objective. To explain how spinal level and age influence disc degeneration arising from endplate fracture. Summary of Background Data. Disc degeneration can be initiated by damage to a vertebral body endplate, but it is unclear why endplate lesions, and patterns of disc degeneration, vary so much with spinal level and age. Methods. One hundred seventy-four cadaveric motion segments, from T7–T8 to L5–S1 and aged 19 to 96 years, were subjected to controlled compressive overload to damage a vertebral body. Stress profilometry was performed before and after damage to quantify changes in intradiscal pressure, and compressive stresses in the annulus. Eighty-six of the undamaged vertebral bodies were then sectioned in the midsagittal plane, and the thickness of the central bony endplate was measured from microradiographs. Regression analysis was used to compare the relative influences of spinal level, age, disc degeneration, and sex on results obtained. Results. Compressive overload caused endplate fracture at an average force of 3.4 kN, and reduced motion segment height by an average 1.88 mm. Pressure loss in the adjacent nucleus pulposus decreased from 93% at T8–T9 to 38% at L4–L5 (R2 = 22%, P < 0.001), and increased with age (R2 = 19%, P < 0.001), especially in male specimens. Stress concentrations in the posterior annulus increased after endplate fracture, with the effect being greatest at upper spinal levels (R2 = 7%, P < 0.001). Endplate thickness increased by approximately 50% between T11 and L5 (R2 = 21%, P < 0.001). Conclusion. Endplate fracture creates abnormal stress distributions in the adjacent intervertebral disc, increasing the risk of internal disruption and degeneration. Effects are greatly reduced in the lower lumbar spine, and in young specimens, primarily because of differences in nucleus volume, and materials properties, respectively. Disc degeneration between L4 and S1 may often be unrelated to endplate fracture. Level of Evidence: N/

Relation of vertebral deformities to bone density, structure, and strength.

Because they are not reliably discriminated by areal bone mineral density (aBMD) measurements, it is unclear whether minimal vertebral deformities represent early osteoporotic fractures. To address this, we compared 90 postmenopausal women with no deformity (controls) with 142 women with one or more semiquantitative grade 1 (mild) deformities and 51 women with any grade 2-3 (moderate/severe) deformities. aBMD was measured by dual-energy X-ray absorptiometry (DXA), lumbar spine volumetric bone mineral density (vBMD) and geometry by quantitative computed tomography (QCT), bone microstructure by high-resolution peripheral QCT at the radius (HRpQCT), and vertebral compressive strength and load-to-strength ratio by finite-element analysis (FEA) of lumbar spine QCT images. Compared with controls, women with grade 1 deformities had significantly worse values for many bone density, structure, and strength parameters, although deficits all were much worse for the women with grade 2-3 deformities. Likewise, these skeletal parameters were more strongly associated with moderate to severe than with mild deformities by age-adjusted logistic regression. Nonetheless, grade 1 vertebral deformities were significantly associated with four of the five main variable categories assessed: bone density (lumbar spine vBMD), bone geometry (vertebral apparent cortical thickness), bone strength (overall vertebral compressive strength by FEA), and load-to-strength ratio (45-degree forward bending ÷ vertebral compressive strength). Thus significantly impaired bone density, structure, and strength compared with controls indicate that many grade 1 deformities do represent early osteoporotic fractures, with corresponding implications for clinical decision making

Biomechanical comparison of a novel castless arthrodesis plate with -plate and cross pin techniques for canine partial carpal arthrodesis

SummaryObjectives: To describe a novel canine castless partial carpal arthrodesis plate (par-CA) and its ex vivo biomechanical comparison with T-plate and cross pinning techniques for canine partial carpal arthrodesis.Methods: The three implant systems were applied to three cohorts of six forelimbs from Greyhounds euthanatized for reasons unrelated to the study. Intercarpal and carpometacarpal palmar fibrocartilage and ligaments were sectioned. Potentiometers were applied between the radial carpal and third metacarpal bones to measure micromotion, and limbs were loaded at 30% of bodyweight at 1 Hertz for 10,000 cycles on a servo-hydraulic universal testing machine. Following assessment of micromotion, limbs were loaded to failure at 20 mm/s and ultimate strength, ultimate displacement, and stiffness were measured.Results: The T-plate (p &lt;0.01) and par-CA (p &lt;0.01) had reduced micromotion relative to the cross pin constructs but there was no significant difference between the control, T-plate and par-CA constructs. There was no significant difference in ultimate strength between constructs. Ultimate displacement was reduced in the plated constructs. Stiffness did not differ between constructs.Clinical significance: The novel par-CA construct was biomechanically similar to the T-plate and both were superior to cross pins in resisting micromotion. There was no difference in load at failure between constructs. The par-CA plate permits radial and ulnar carpal bone compression, a more distal location of the plate to limit impingement, and placement of screws in two metacarpal bones; features which may offer clinical benefits over T-plate fixation.</jats:p

Bone creep can cause progressive vertebral deformity

Introduction Vertebral deformities in elderly people are conventionally termed “fractures”, but their onset is often insidious, suggesting that time-dependent (creep) processes may also be involved. Creep has been studied in small samples of bone, but nothing is known about creep deformity of whole vertebrae, or how it might be influenced by bone mineral density (BMD). We hypothesise that sustained compressive loading can cause progressive and measurable creep deformity in elderly human vertebrae. Methods 27 thoracolumbar “motion segments” (two vertebrae and the intervening disc and ligaments) were dissected from 20 human cadavers aged 42–91 yrs. A constant compressive force of approximately 1.0 kN was applied to each specimen for either 0.5 h or 2 h, while the anterior, middle and posterior heights of each of the 54 vertebral bodies were measured at 1 Hz using a MacReflex 2D optical tracking system. This located 6 reflective markers attached to the lateral cortex of each vertebral body, with resolution better than 10 μm. Experiments were at laboratory temperature, and polythene film was used to minimise water loss. Volumetric BMD was calculated for each vertebral body, using DXA to measure mineral content, and water immersion for volume. Results In the 0.5 h tests, creep deformation in the anterior, middle and posterior vertebral cortex averaged 4331, 1629 and 614 micro-strains respectively, where 10,000 micro-strains represents 1% loss in height. Anterior creep strains exceeded posterior (P < 0.01) so that anterior wedging of the vertebral bodies increased, by an average 0.08° (STD 0.14°). Similar results were obtained after 2 h, indicating that creep rate slowed considerably with time. Less than 40% of the creep strain was recovered after 2 h. Increases in anterior wedging during the 0.5 h creep test were inversely proportional to BMD, but only in a selected sub-set of 20 specimens with average BMD < 0.15 g/cm3 (P = 0.042). Creep deformation caused more than 5% height loss in four vertebrae, three of which had radiographic signs of pre-existing damage. Conclusion Sustained loading can cause progressive anterior wedge deformity in elderly human vertebrae, even in the absence of fracture

Influence of Vertical Trabeculae on the Compressive Strength of the Human Vertebra

Vertebral strength, a key etiologic factor of osteoporotic fracture, may be affected by the relative amount of vertically oriented trabeculae. To better understand this issue, we performed experimental compression testing, high-resolution micro–computed tomography (µCT), and micro–finite-element analysis on 16 elderly human thoracic ninth (T9) whole vertebral bodies (ages 77.5 ± 10.1 years). Individual trabeculae segmentation of the µCT images was used to classify the trabeculae by their orientation. We found that the bone volume fraction (BV/TV) of just the vertical trabeculae accounted for substantially more of the observed variation in measured vertebral strength than did the bone volume fraction of all trabeculae (r2 = 0.83 versus 0.59, p < .005). The bone volume fraction of the oblique or horizontal trabeculae was not associated with vertebral strength. Finite-element analysis indicated that removal of the cortical shell did not appreciably alter these trends; it also revealed that the major load paths occur through parallel columns of vertically oriented bone. Taken together, these findings suggest that variation in vertebral strength across individuals is due primarily to variations in the bone volume fraction of vertical trabeculae. The vertical tissue fraction, a new bone quality parameter that we introduced to reflect these findings, was both a significant predictor of vertebral strength alone (r2 = 0.81) and after accounting for variations in total bone volume fraction in multiple regression (total R2 = 0.93). We conclude that the vertical tissue fraction is a potentially powerful microarchitectural determinant of vertebral strength. © 2011 American Society for Bone and Mineral Research

Total and Visceral Adiposity Are Associated With Prevalent Vertebral Fracture in Women but Not Men at Age 62 Years: The Newcastle Thousand Families Study

Low body weight is an established risk factor for osteoporosis and fracture, but the skeletal risks of higher adiposity are unclear and appear sex‐specific and site‐dependent. The aim of this study was to investigate associations of total fat mass (TFM), visceral adipose tissue (VAT), and C‐reactive protein (CRP) with bone mineral density (BMD) and prevalent vertebral fracture (VF) in men and women aged 62 years. A total of 352 men and women aged 62.5 ± 0.5 years from the Newcastle Thousand Families Study cohort received dual‐energy X‐ray absorptiometry (DXA) evaluations of femoral neck and lumbar spine BMD, of the lateral spine for vertebral fracture assessment, and of the whole body for TFM and VAT (GE Lunar CoreScan, Madison, WI, USA). Plasma CRP, FRAX scores, falls in the last 12 months, and occupation at age 50 years were also included in the analysis. Vertebral fractures were less prevalent in women than in men (odds ratio [OR] = 0.33, p < 0.001) and BMD or FRAX scores did not differ between participants with and without VF. Women with VF were heavier and had higher TFM, VAT, and CRP than women without (p < 0.001). In women, greater (+1 SD) TFM and VAT increased the odds of any grade VF (TFM: OR = 1.06, p = 0.001; VAT: OR = 2.50, p = 0.002), and greater VAT mass increased the odds of prevalent mild VF (OR = 2.60, p = 0.002). In contrast, there were no associations in men. In both sexes, after controlling for body weight, neither VAT nor CRP were associated with BMD. In conclusion, irrespective of BMD, total and visceral adiposity were associated with prevalent VF in women but not in men. High fat mass, particularly if visceral, should be considered when assessing VF risk in women. Risk factors for VF in men require further investigation, particularly given their high prevalence

Linear viscoelasticity - bone volume fraction relationships of bovine trabecular bone

Trabecular bone has been previously recognized as time-dependent (viscoelastic) material, but the relationships of its viscoelastic behaviour with bone volume fraction (BV/TV) have not been investigated so far. Therefore, the aim of the present study was to quantify the time-dependent viscoelastic behaviour of trabecular bone and relate it to BV/TV. Uniaxial compressive creep experiments were performed on cylindrical bovine trabecular bone samples ([Formula: see text] ) at loads corresponding to physiological strain level of 2000 [Formula: see text] . We assumed that the bone behaves in a linear viscoelastic manner at this low strain level and the corresponding linear viscoelastic parameters were estimated by fitting a generalized Kelvin–Voigt rheological model to the experimental creep strain response. Strong and significant power law relationships ([Formula: see text] ) were found between time-dependent creep compliance function and BV/TV of the bone. These BV/TV-based material properties can be used in finite element models involving trabecular bone to predict time-dependent response. For users’ convenience, the creep compliance functions were also converted to relaxation functions by using numerical interconversion methods and similar power law relationships were reported between time-dependent relaxation modulus function and BV/TV

Subregional DXA-derived vertebral bone mineral measures are stronger predictors of failure load in specimens with lower areal bone mineral density, compared to those with higher areal bone mineral density

Measurement of areal bone mineral density (aBMD) in intravertebral subregions may increase the diagnostic sensitivity of dual-energy X-ray absorptiometry (DXA)-derived parameters for vertebral fragility. This study investigated whether DXA-derived bone parameters in vertebral subregions were better predictors of vertebral bone strength in specimens with low aBMD, compared to those with higher aBMD. Twenty-five lumbar vertebrae (15 embalmed and 10 fresh-frozen) were scanned with posteroanterior- (PA) and lateral-projection DXA, and then mechanically tested in compression to ultimate failure. Whole-vertebral aBMD and bone mineral content (BMC) were measured from the PA- and lateral-projection scans and within 6 intravertebral subregions. Multivariate regression was used to predict ultimate failure load by BMC, adjusted for vertebral size and specimen fixation status across the whole specimen set, and when subgrouped into specimens with low aBMD and high aBMD. Adjusted BMC explained a substantial proportion of variance in ultimate vertebral load, when measured over the whole vertebral area in lateral projection (adjusted R2 0.84) and across the six subregions (ROIs 2–7) (adjusted R2 range 0.58–0.78). The association between adjusted BMC, either measured subregionally or across the whole vertebral area, and vertebral failure load, was increased for the subgroup of specimens with identified ‘low aBMD’, compared to those with ‘high aBMD’, particularly in the anterior subregion where the adjusted R2 differed by 0.44. The relative contribution of BMC measured in vertebral subregions to ultimate failure load is greater among specimens with lower aBMD, compared to those with higher aBMD, particularly in the anterior subregion of the vertebral body