Elizabeth R. Myers

DMP1 Depletion Decreases Bone Mineralization In Vivo: An FTIR Imaging Analysis†

The role of DMP1 in mineralization was analyzed by comparing bone mineral and matrix properties in dmp1‐null female mice to heterozygous and wildtype controls by FTIR imaging spectroscopy. The observed decreased mineral content in dmp1 null mice indicates a key role for dmp1 in bone mineralization. Indirect effects of DMP1 on other systems also determine the KO phenotype.

Combined Bone Morphogenetic Protein-2 and −7 Gene Transfer Enhances Osteoblastic Differentiation and Spine Fusion in a Rodent Model†

To enhance the osteogenic activity of BMP, combination BMP2 and BMP7 gene transfer was performed. This approach led to a significant increase in osteoblastic differentiation of mesenchymal precursors compared with single BMP gene transfer in vitro. When tested in 78 rats, combination gene transfer enhanced mechanically stable spine fusion and bone formation rate versus single BMP gene transfer.

Use of FTIR Spectroscopic Imaging to Identify Parameters Associated With Fragility Fracture

BMD does not entirely explain an individuals risk of fracture. The purpose of this study was to assess whether specific differences in spatially resolved bone composition also contribute to fracture risk. These differences were assessed using Fourier transform infrared spectroscopic imaging (FTIRI) and analyzed through multiple logistic regression. Models were constructed to determine whether FTIRI measured parameters describing mineral content, mineral crystal size and perfection, and collagen maturity were associated with fracture. Cortical and cancellous bone were independently evaluated in iliac crest biopsies from 54 women (32 with fractures, 22 without) who had significantly different spine but not hip BMDs and ranged in age from 30 to 83 yr. The parameters that were significantly associated with fracture in the model were cortical and cancellous collagen maturity (increased with increased fracture risk), cortical mineral/matrix ratio (higher with increased fracture risk), and cancellous crystallinity (increased with increased fracture risk). As expected, because of its correlation with cortical but not cancellous bone density, hip BMD was significantly associated with fracture risk in the cortical but not the cancellous model. This research suggests that additional parameters associated with fracture risk should be targeted for therapies for osteoporosis.

Bone Mass Is Preserved and Cancellous Architecture Altered Due to Cyclic Loading of the Mouse Tibia After Orchidectomy

Introduction: The study of adaptation to mechanical loading under osteopenic conditions is relevant to the development of osteoporotic fracture prevention strategies. We previously showed that loading increased cancellous bone volume fraction and trabecular thickness in normal male mice. In this study, we tested the hypothesis that cyclic mechanical loading of the mouse tibia inhibits orchidectomy (ORX)‐associated cancellous bone loss.

Assessment of bone mineral density in adults and children with Marfan syndrome

Recent studies indicate that decreased bone mineral density (BMD) occurs in the spine, femoral necks and greater trochanters of some adults and children with Marfan syndrome. Because there is uncertainty regarding the BMD status of patients with Marfan syndrome, we undertook an analysis of BMD in both adults and children with Marfan syndrome. Dual energy X-ray absorptiometry analysis was performed on a convenience sample of 51 patients (30 adults and 21 children) with diagnosed Marfan syndrome from 1993 to 2000. T-Scores (i.e. the number of standard deviations above or below the average normal peak bone density) were determined for comparison of adults. Mean±SD of individual BMD values were used for comparison of the data of children. Compared to standard values obtained from normal adult patients, adult males with Marfan syndrome demonstrated significantly reduced femoral neck BMD with an average T-score of -1.54 (P<0.001), diagnostic of osteopenia. Although osteopenia and osteoporosis were observed in several middle aged and pre- and postmenopausal women, the average T-score value for adult females and children were within normal limits. The etiology and full significance of decreased BMD in adult male patients with Marfan syndrome remain uncertain at the present time. Our results lead us to question the value of aggressive BMD evaluations by DXA in these patients, particularly prior to reaching mid-age. Further investigations will be required to shed insights into the natural history of BMD in adults and children with Marfan syndrome. Any application of bone mineral replacement therapy such as bisphosphonate, selective estrogen receptor modulators, hormone replacement therapy and vitamin D in these patients may be premature based on the existing evidence.

High-dose alendronate uncouples osteoclast and osteoblast function: a study in a rat spine pseudarthrosis model.

The effect of alendronate on osteoclast and osteoblast function was studied in a novel spine pseudarthrosis model in rats. Sixty-three Sprague-Dawley rats were divided into three groups: control group (saline), therapeutic dose group (1 μg/kg/week), and one-log overdose group (10 μg/kg/week). Animals had L4-L5 posterior intertransverse process fusion with limited bone graft and were sacrificed at 2, 4, and 6 weeks. Manual palpation showed no notable differences among groups. Treatment group radiographic scores were equal to or better than control group scores and were higher than the overdose group at 2 and 6 weeks. Qualitatively, limited histologic remodeling and poor osteoclastic and osteoblastic function were noted in the alendronate treated groups. Quantitative histologic analysis showed fewer osteoclasts in the therapeutic and high-dose groups (p < 0.001). The percent osteoblasts per bone surface area was lower in the high-dose group (p < 0.05). The results suggest that the effect of alendronate was dose dependent and animal model dependent and that supranormal doses of alendronate had a deleterious effect on osteoclastic and osteoblastic function in this model.

The aging spine: new technologies and therapeutics for the osteoporotic spine

Osteoporosis results in low-energy fractures of the spine. The load necessary to cause a vertebral fracture is determined by the characteristics related to the vertebral body structure, mineral content, and quality of bone. Radiographic techniques centered on dual X-ray absorptiometry (DXA) permit a determination of bone mass and fracture risk. Current medical therapies principally using bisphosphonate and pulsatile PTH profoundly decrease the risk of fracture (50+%). Fall prevention strategies can further decrease the possibility of fracture. A comprehensive approach to osteoporosis can favorably alter the disease.

Assessing the Stiffness of Spinal Fusion in Animal Models

The clinical goal of spinal fusion is to reduce motion and the associated pain. Therefore, measuring motion under loading is critical. The purpose of this study was to validate four-point bending as a means to mechanically evaluate simulated fusions in dog and rabbit spines. We hypothesized that this method would be more sensitive than manual palpation and would be able to distinguish unilateral vs bilateral fusion. Spines from four mixed breed dogs and four New Zealand white rabbits were used to simulate posterolateral fusion with polymethyl methacrylate as the fusion mass. We performed manual palpation and nondestructive mechanical testing in four-point bending in four planes of motion: flexion, extension, and right and left bending. This testing protocol was used for each specimen in three fusion modes: intact, unilateral, and bilateral fusion. Under manual palpation, all intact spines were rated as not fused, and all unilateral and bilateral simulated fusions were rated as fused. In four-point bending, dog spines were significantly stiffer after unilateral fusion compared with intact in all directions. Additionally, rabbit spines were stiffer in flexion and left bending after unilateral fusion. All specimens exhibited significant differences between intact and bilateral fusion except the rabbit in extension. For unilateral vs bilateral fusion, significant differences were present for right bending in the dog model and for flexion in the rabbit. Unilateral fusion can provide enough stability to constitute a fused grade by manual palpation but may not provide structural stiffness comparable to bilateral fusion.

Mechanical advantage of defects healed with demineralized bone matrix over autogenous bone graft

Purpose of study: The purpose of this investigation was to compare the mechanical stiffness and strength of healed, grafted defects using either the classical method of autogenous bone graft or demineralized bone matrix. Methods used: Critical 2-cm defects were created in the ulnas of 75 6-month-old male New Zealand White Rabbits (3.5 to 4.0 kg). Defects were treated with approximately 1 cc of graft material: demineralized bone matrix (DBM) plug, DBM + bone marrow (BM), devitalized DBM (dDBM), dDBM + BM, BM, empty or autogenous bone graft (ABG). Animals were radiographed at 0, 3, 6, 9 and at sacrifice at 12 weeks. Sixty-nine rabbits completed the study. The six deaths were the result of surgical complications. Only grafts that were graded as a union were mechanically tested. The radius transected and constructs were tested in torsion to failure. The torsional stiffness and maximum failure torque for each group were compared by analysis of variance with a pairwise comparison test using a Bonferroni adjustment. of findings: The radiographic findings at 12 weeks showed complete bridging of the defect in the DBM and DBM + BM groups. In contrast, healing was not as complete in the dDBM-treated defects. Defects treated with dDBM and bone marrow did considerably better. The BM group displayed complete bridging but without the uniform surface contour seen with the DBM groups. Defects treated with ABG were bridged, although difficult to analyze radiographically because of the endogenous mineral present within the graft. There was no statistical difference between the union rates except for the dDBM and empty groups. The torsional stiffness of the DBM + BM group was twice that of ABG (p<.01). There were no differences found in the maximum torque. Relationship between findings and existing knowledge: This study has shown that treatment of defects with a structural osteoinductive/osteoconductive scaffold, such as a DBM matrix plug in the presence of bone marrow, results in mechanically stronger bone at 12 weeks than defects treated with ABG alone. Although these results were obtained in a long bone model, they are consistent with Bodens results in a rabbit spine fusion model using structural DBM scaffolds and autograft, and suggest bone marrow would be useful adjunct in enhancing spine fusion. Overall significance of findings: In a clearly definable model, we were able to show superior material properties in comparison to the classical standard, ABG. Disclosures: No disclosures. Conflict of interest: Celeste Abjornson, grant research support; Joseph Lane, grant research support, Osteotech