Augmentation of failed human vertebrae with critical un-contained lytic defect restores their structural competence under functional loading: An experimental study.

BACKGROUND: Lytic spinal lesions reduce vertebral strength and may result in their fracture. Vertebral augmentation is employed clinically to provide mechanical stability and pain relief for vertebrae with lytic lesions. However, little is known about its efficacy in strengthening fractured vertebrae containing lytic metastasis. METHODS: Eighteen unembalmed human lumbar vertebrae, having simulated uncontained lytic defects and tested to failure in a prior study, were augmented using a transpedicular approach and re-tested to failure using a wedge fracture model. Axial and moment based strength and stiffness parameters were used to quantify the effect of augmentation on the structural response of the failed vertebrae. Effects of cement volume, bone mineral density and vertebral geometry on the change in structural response were investigated. FINDINGS: Augmentation increased the failed lytic vertebral strength [compression: 85% (P<0.001), flexion: 80% (P<0.001), anterior-posterior shear: 95%, P<0.001)] and stiffness [(40% (P<0.05), 53% (P<0.05), 45% (P<0.05)]. Cement volume correlated with the compressive strength (r(2)=0.47, P<0.05) and anterior-posterior shear strength (r(2)=0.52, P<0.05) and stiffness (r(2)=0.45, P<0.05). Neither the geometry of the failed vertebrae nor its pre-fracture bone mineral density correlated with the volume of cement. INTERPRETATION: Vertebral augmentation is effective in bolstering the failed lytic vertebrae compressive and axial structural competence, showing strength estimates up to 50-90% of historical values of osteoporotic vertebrae without lytic defects. This modest increase suggests that lytic vertebrae undergo a high degree of structural damage at failure, with strength only partially restored by vertebral augmentation. The positive effect of cement volume is self-limiting due to extravasation.

Effectiveness of combination use of antibiotic-loaded PerOssal with spinal surgery in patients with spondylodiscitis.

Degradable composites of calcium sulphate and nanoparticulate hydroxyapatite (PerOssal) have shown promising results in vitro. Here we investigated the handling, efficacy and compatibility of PerOssal when loaded with gentamicin or vancomycin in 19 patients with spondylodiscitis in vivo. So far, 12 patients who were followed up over at least 1 year have shown a normalization of the infection parameters, no more bone loss in the affected regions and a bony fusion after 3-6 months postoperatively. No revision surgery was related to the use of PerOssal. Locally there were no signs of an ongoing infection. This study demonstrates encouraging results regarding handling, resorption, biocompatibility and antibiotic release using PerOssal pellets in vivo.

Bone volume fraction explains the variation in strength and stiffness of cancellous bone affected by metastatic cancer and osteoporosis.

Preventing nontraumatic fractures in millions of patients with osteoporosis or metastatic cancer may significantly reduce the associated morbidity and reduce health-care expenditures incurred by these fractures. Predicting fracture occurrence requires an accurate understanding of the relationship between bone structure and the mechanical properties governing bone fracture that can be readily measured. The aim of this study was to test the hypothesis that a single analytic relationship with either bone tissue mineral density or bone volume fraction (BV/TV) as independent variables could predict the strength and stiffness of normal and pathologic cancellous bone affected by osteoporosis or metastatic cancer. After obtaining institutional review board approval and informed consent, 15 patients underwent excisional biopsy of metastatic prostate, breast, lung, ovarian, or colon cancer from the spine and/or femur to obtain 41 metastatic cancer specimens. In addition, 96 noncancer specimens were excised from 43 age- and site-matched cadavers. All specimens were imaged using micro-computed tomography (micro-CT) and backscatter emission imaging and tested mechanically by uniaxial compression and nanoindentation. The minimum BV/TV, measured using quantitative micro-CT, accounted for 84% of the variation in bone stiffness and strength for all cancellous bone specimens. While relationships relating bone density to strength and stiffness have been derived empirically for normal and osteoporotic bone, these relationships have not been applied to skeletal metastases. This simple analytic relationship will facilitate large-scale screening and prediction of fracture risk for normal and pathologic cancellous bone using clinical CT systems to determine the load capacity of bones altered by metastatic cancer, osteoporosis, or both.

The effect of cement augmentation on the geometry and structural response of recovered osteopenic vertebrae: an anterior-wedge fracture model.

STUDY DESIGN: The efficacy of cement augmentation in restoring the geometry and structural competence of failed thoracic and lumbar human vertebrae under mechanical loads was studied. OBJECTIVES: To quantify whether cement augmentation restores and maintains the geometry and structural competence of failed osteopenic vertebrae and to assess the contribution of vertebral geometry to the achieved augmentation. SUMMARY OF BACKGROUND DATA: Cement augmentation of failed vertebrae was clinically shown to alleviate significant pain and functional impairments associated with vertebral fragility fractures. However, the procedure's efficacy in restoring the structural response of the failed vertebrae and maintaining the achieved geometry under functional loads remains unclear. METHODS: Nineteen thoracic and lumbar human vertebrae were tested to failure under compression-flexion loading. The vertebrae were allowed to recover, were retested to failure, augmented with Polymethylmethacrylate and again retested to failure. Repeated measures analysis was used to compare the change in vertebral geometry and structural response, defined as the multiplanar force and moment response of the vertebra to the imposed deformation, at each of the test stages. Linear regression was used to assess the role of the geometry of the failed vertebrae in affecting the outcome of augmentation. RESULTS: Augmentation significantly increased the compressive (228%) and flexion (118%) strength of the failed vertebrae and achieved a significant, albeit partial, restoration of vertebral geometry. However, the structural response of the failed vertebrae was markedly altered, whereas under applied loads, the achieved height restoration was significantly diminished. Although the geometry of the fractured vertebral body was associated with the degree of restoration of the vertebral body afteraugmentation, it was not correlated with the change in the structural parameters. CONCLUSION: Augmentation increases the structural competence of failed vertebrae and to a degree, restores their geometry. However, the structural response of the augmented vertebrae was significantly modified. Furthermore, the augmented vertebrae were unable to maintain the degree of geometry restoration under load.

Effects of thresholding techniques on microCT-based finite element models of trabecular bone.

Microimaging based finite element analysis is widely used to predict the mechanical properties of trabecular bone. The choice of thresholding technique, a necessary step in converting grayscale images to finite element models, can significantly influence the predicted bone volume fraction and mechanical properties. Therefore, we investigated the effects of thresholding techniques on microcomputed tomography (micro-CT) based finite element models of trabecular bone. Three types of thresholding techniques were applied to 16-bit micro-CT images of trabecular bone to create three different models per specimen. Bone volume fractions and apparent moduli were predicted and compared to experimental results. In addition, trabecular tissue mechanical parameters and morphological parameters were compared among different models. Our findings suggest that predictions of apparent mechanical properties and structural properties agree well with experimental measurements regardless of the choice of thresholding methods or the format of micro-CT images.

Minimizing the surgical approach in patients with spondylitis.

Minimizing the surgical approach in treating patients with spinal infections by using local antibiotic treatment and avoiding a ventral approach reduces the anesthesia and surgical risks in patients with comorbidities. In this study we used calcium sulphate pellets (OsteoSet T and the OsteoSet Bone-void Filler kit) as a delivery system for different antibiotics. Of a group of 32 patients with histologically and microbiologically diagnosed spondylitis, a cohort of 16 patients was treated by just a dorsal surgical approach in combination with a local antibiotic delivery system. Of these 16 patients, 14 patients showed a normalization of the infection parameters, no more bone loss in the spondylitic region, and a bony fusion after 6 to 9 months postoperatively. Two patients died from septic circumstances 4 and 6 weeks postoperatively. Two patients had to have one revision surgery because of a seroma; no other complications caused by the calcium sulphate pellets were observed. The use of calcium sulphate pellets as antibiotic delivery system allows a controlled local antibiotic therapy with an osteoconductive material in combination with a minimized surgical approach. Furthermore, calcium sulphate pellets have proven their reliable capability as bone void filler.

In vivo bone regeneration with injectable calcium phosphate biomaterial: a three-dimensional micro-computed tomographic, biomechanical and SEM study.

This in vivo study investigated the efficiency of an injectable calcium phosphate bone substitute (IBS) for bone regenerative procedures through non-destructive three-dimensional (3D) micro-tomographic (microCT) imaging, biomechanical testing with a non-destructive micro-indentation technique and 2D scanning electron microscopy (SEM) analysis. The injectable biomaterial was obtained by mixing a biphasic calcium phosphate (BCP) ceramic mineral phase and a cellulosic polymer. The BCP particles were 200-500 microm or 80-200 microm in diameter. The injectable material was implanted for 6 weeks into critical-sized bone defects at the distal end of rabbit femurs. Extensive new bone apposition was noted with both 2D and 3D techniques. Micro-CT showed that newly formed bone was in perfect continuity with the trabecular host bone structure and demonstrated the high interconnectivity of the restored bone network. For both IBS formulations, SEM and microCT gave very close measurements. The only detected significant difference concerned the amount of newly formed bone obtained with IBS 80-200 that appeared significantly higher with microCT analysis than with SEM (p=0.00007). Student t-tests did not show any significant difference in the amount of newly formed bone and remaining ceramic obtained from microCT analysis or SEM. Regression analysis showed satisfactory correlation between both the amount of newly formed bone and remaining ceramic obtained from microCT or SEM. For IBS 200-500, the newly formed bone rate inside the defect was 28.0+/-5.2% with SEM and yield strength of the samples was 18.8+/-5.4 MPa. For IBS 80-200, the newly formed bone rate inside the defect was 31.7+/-5.1% with SEM and yield strength of the samples was 26.8+/-4.5 MPa. Yield strength appeared well correlated with the amount of newly formed bone, specially observed with microCT. This study showed the ability of non-destructive techniques to investigate biological and mechanical aspects of bone replacement with injectable biomaterials.

Trabecular bone response to mechanical and parathyroid hormone stimulation: the role of mechanical microenvironment.

UNLABELLED: Bone response under combined mechanical and PTH stimuli is important in osteoporosis. A rat tail animal model with computer modeling was used to examine bone response to loading and PTH. PTH enhances and sustains increased bone formation rate, which directly correlates to mechanical microenvironment, suggesting beneficial effects of combined PTH treatment and exercise in preventing osteoporosis. INTRODUCTION: Using an in vivo rat tail vertebra model combined with a specimen-specific, high-resolution microcomputed tomography (microCT)-based finite element analysis (FEA) technique, trabecular bone response to combined dynamic compressive loading and parathyroid hormone (PTH) stimulation was characterized. MATERIALS AND METHODS: Two hundred twenty-four male Sprague-Dawley rats were randomly divided into seven treatment groups: (1) Control, (2) vehicle + 0N, (3) PTH + 0N, (4) vehicle + 50N, (5) PTH + 50N, (6) vehicle + 100N, and (7) PTH + 100N, with three treatment durations (1, 2, or 4 weeks). Rat PTH(1-34) was administered daily in the PTH-stimulated groups approximately 3 h before daily mechanical stimulation with 0, 50, or 100N dynamic compressive loading. microCT-based FEA was performed for each loaded vertebra after death. Bone histomorphometry was performed on trabecular bone with double fluorochrome labeling to assess bone formation. RESULTS: Daily mechanical loading or PTH administration significantly increased bone formation rate (BFR) compared with control or V + 0N with significant increases in both mineral apposition rate (MAR) and labeled bone surface (LS/BS). PTH, when combined with mechanical loading, enhanced BFR mainly through a significant increase in MAR after the first week and through a significant increase in LS/BS after 2 and 4 weeks. Synergistic effects in BFR were present when PTH was combined with mechanical loading, especially after 2 and 4 weeks, where the increase in BFR was sustained. However, when either PTH or mechanical loading was the only stimulus, the bone formation response diminished to the level of Control animals after 4 weeks. Furthermore, significant correlations were observed between the bone formation indices and trabecular bone tissue mechanical microenvironments at 1 and 2 weeks, with PTH administration enhancing and sustaining these correlations into 4 weeks. CONCLUSIONS: The synergistic effects of combined PTH and mechanical stimulation on trabecular bone formation rate suggest a potential benefit for combined PTH administration and exercise in the treatment of osteoporosis.

The cortical thickness of the proximal humeral diaphysis predicts bone mineral density of the proximal humerus.

The operative treatment of fractures of the proximal humerus can be complicated by poor bone quality. Our aim was to evaluate a new method which allows prediction of the bone quality of the proximal humerus from radiographs. Anteroposterior radiographs were taken of 19 human cadaver humeri. The cortical thickness was measured at two levels of the proximal humeral diaphysis. The bone mineral density (BMD) was determined for the humeral head (HH), the surgical neck (SN), the greater tuberosity (GT) and lesser tuberosity (LT) using dual-energy x-ray absorptiometry. The mean cortical thickness was 4.4 +/- 1.0 mm. Specimens aged 70 years or less had a significantly higher cortical thickness than those aged over 70 years. A significant positive correlation was found between cortical thickness and the BMD for each region of interest. The cortical thickness of the proximal diaphysis is a reliable predictor of the bone quality of the proximal humerus.

Three-dimensional quantitation of periradicular bone destruction by micro-computed tomography.

We have previously shown that two-dimensional, high-resolution, micro-computed tomography is a rapid, reproducible, and noninvasive method for measuring periradicular bone resorption in mice, giving results virtually identical to histology. In this study, we determined whether a three-dimensional volumetric quantitation of bone resorption could be achieved and whether this correlates with two-dimensional measurements. Periradicular lesions were induced in the lower first molars of mice by pulp exposure and infection; unexposed teeth served as controls. Mandibles were harvested on day 21 and subjected to: (a) three-dimensional micro-computed tomography imaging; and (b) conventional histology. Using a three-dimensional model and a semiautomatic contouring algorithm, we determined three-dimensional void volume, void surface, void thickness, and the standard deviation of the thickness distribution. The results showed a significant correlation between lesion void volume and two-dimensional lesion area by histology (r2 = 0.73), as well as high correlations between void volume and void thickness (r2 = 0.86) and standard deviation of the void thickness (r2 = 0.87), but no relationship with void surface. These results show that three-dimensional analysis of micro-computed tomography images is highly correlated with two-dimensional cross-sectional measures of periradicular lesions. Nevertheless, micro-computed tomography allows assessment of additional microstructural features as well as sub-regional analysis of lesion development.

Does simvastatin stimulate bone formation in vivo?

BACKGROUND: Statins, potent compounds that inhibit cholesterol synthesis in the liver have been reported to induce bone formation, both in tissue culture and in rats and mice. To re-examine potential anabolic effects of statins on bone formation, we compared the activity of simvastatin (SVS) to the known anabolic effects of PTH in an established model of ovariectomized (OVX) Swiss-Webster mice. METHODS: Mice were ovariectomized at 12 weeks of age (T0), remained untreated for 5 weeks to allow development of osteopenia (T5), followed by treatment for 8 weeks (T13). Whole, trabecular and cortical femoral bone was analyzed by micro-computed tomography (micro CT). Liquid chromatography/mass spectrometry (LC/MS) was used to detect the presence of SVS and its active metabolite, simvastatin beta-hydroxy acid (SVS-OH) in the mouse serum. RESULTS: Trabecular BV/TV at T13 was 4.2 fold higher in animals treated with PTH (80 micro-g/kg/day) compared to the OVX-vehicle treated group (p < 0.001). However, the same comparison for the SVS-treated group (10 mg/kg/day administered by gavage) showed no significant difference (p = NS). LC/MS detected SVS and SVS-OH in mouse serum 20 minutes after gavage of 100 mg SVS. A serum osteocalcin assay (OC) demonstrated that neither bone formation nor osteoblast activity is significantly enhanced by SVS treatment in this in vivo study. CONCLUSIONS: While PTH demonstrated the expected anabolic effect on bone, SVS failed to stimulate bone formation, despite our verification by LC/MS of the active SVS-OH metabolite in mouse serum. While statins have clear effects on bone formation in vitro, the formulation of existing 'liver-targeted' statins requires further refinement for efficacy in vivo.

Deletion of the GATA domain of TRPS1 causes an absence of facial hair and provides new insights into the bone disorder in inherited tricho-rhino-phalangeal syndromes.

GATA transcription factors mediate cell differentiation in diverse tissues, and their dysfunction is associated with certain congenital human disorders. The six classical vertebrate GATA proteins, GATA-1 to GATA-6, are highly homologous, bear two tandem zinc fingers of the C(4) (GATA) type, and activate transcription. TRPS1, the only other vertebrate protein with the GATA motif, is a large, multitype zinc finger protein that harbors a single DNA-binding GATA domain and represses transcription. Monoallelic TRPS1 mutations cause two dominantly inherited human developmental disorders of the hair, face, and digits, tricho-rhino-phalangeal syndrome (TRPS) types I (MIM 190350) and III (MIM 190351); missense GATA domain mutations account for the more severe type III form. Here we report that heterozygous mice with deletions of the TRPS1 GATA domain (TRPS1(+/Deltagt)) display facial anomalies that overlap with findings for TRPS, whereas TRPS1(Deltagt/Deltagt) mice additionally reveal a complete absence of vibrissae. Unexpectedly, TRPS1(Deltagt/Deltagt) mice die of neonatal respiratory failure resulting from abnormalities of the thoracic spine and ribs. Heterozygotes also develop thoracic kyphoscoliosis with age and reveal structural deficits in cortical and trabecular bones. These findings directly implicate the GATA type zinc finger of TRPS1 in regulation of bone and hair development and suggest that skeletal abnormalities emphasized in descriptions of TRPS are only the extreme manifestations of a generalized bone dysplasia.

Osteoblast-specific knockout of the insulin-like growth factor (IGF) receptor gene reveals an essential role of IGF signaling in bone matrix mineralization.

To examine the local actions of IGF signaling in skeletal tissue in a physiological context, we have used Cre-mediated recombination to disrupt selectively in mouse osteoblasts the gene encoding the type 1 IGF receptor (Igf1r). Mice carrying this bone-specific mutation were of normal size and weight but, in comparison with normal siblings, demonstrated a striking decrease in cancellous bone volume, connectivity, and trabecular number, and an increase in trabecular spacing. These abnormalities correlated with a striking decrease in the rate of mineralization of osteoid that occurred despite an unexpected osteoblast and osteoclast hyperactivity, detected from the significant increments in both osteoblast and erosion surfaces. Our findings indicate that IGF1 is essential for coupling matrix biosynthesis to sustained mineralization. This action is likely to be particularly important during the pubertal growth spurt when rapid bone formation and consolidation are required.