Canine Cancellous Bone Research Articles

Identification of effective elastic modulus using modal analysis; application to canine cancellous bone

Mechanical properties of cancellous bone is of increasing interest due to its involvement in aging pathologies and oncology. Characterization of fragile bone tissue is challenging and available methodologies include quasi-static compressive tests of small size specimens, ultrasound and indentation techniques. We hypothesized that modal analysis of flexure beams could be a complementary methodology to obtain Young modulus.The sampling methodology was adapted such that the uniqueness of the linear dynamic response was available to determine the elastic modulus from natural frequencies and mode shapes. In a first step, the methodology was validated using a synthetic bone model as control. Then, water-jet cutting allowed collecting fourteen small beam-like specimens in canine distal femurs. X-ray microtomography confirmed the microarchitecture preservation, the homogeneity and the isotropy at the specimen scale to derive effective properties. The first natural frequency in clamped-free boundary conditions was used to obtain mean values of Young modulus, which ranged from 210 MPa to 280 MPa depending on the specimen collection site. Experimental tests were rapid and reproducible and our preliminary results were in good agreement with literature data. In conclusion, beam modal analysis could be considered for exploring mechanical properties of fragile and scarce biological tissues.

The effect of hydroxyapatite on bone ingrowth into porous-coated titanium implants.

Two different groups of hydroxyapatite (HA) coated and uncoated porous titanium implants, 250-350 m and 500-700 m diameter beads, were press-fit in femoral canine cancellous bone. After 12 weeks, the dogs were euthanized and histomorphometric backscattered electron microscopy studies were carried out. Comparing HA-coated versus uncoated implants in the 250-350 m bead diameter group percentage of bone (P=0.01) and bone index (P=0.01), were higher in the HA-coated implants. Comparing HA-coated versus uncoated implants in the 500-700 m bead diameter group bone ingrowth (P=0.01) and bone depth penetration (P=0.008), were higher in HA-coated samples. It can be concluded that the HA coating was an effective method to improve bone formation and ingrowth in the porous implants. (Hip International 2002; 2: 153-7).

Effect of pilot hole diameter and tapping on insertion torque and axial pullout strength of 4.0-mm cancellous bone screws

To evaluate the effects of pilot hole diameter and tapping on insertion torque and axial pullout strength of 4.0-mm cancellous bone screws in a synthetic canine cancellous bone substitute. 75 synthetic cancellous bone blocks (15 blocks/group). For groups 1 through 5, screw size-pilot hole diameter combinations were 3.5-2.5 mm (cortical screws), 4.0-2.5 mm, 4.0-2.5 mm, 4.0-2.0 mm, and 4.0-2.0 mm, respectively. Holes were tapped in groups 1, 2, and 4 only (tap diameter, 3.5, 4.0, and 4.0 mm, respectively). One 70-mm-long screw was inserted into each block; in a servohydraulic materials testing machine, the screw was extracted (rate, 5 mm/min) until failure. Mean group values of maximum insertion torque, axial pullout strength, yield strength, and stiffness were determined. Mean maximum insertion torque differed significantly among the 5 groups; the group 5 value was greatest, followed by group 3, 4, 2, and 1 values. Group 3, 4, and 5 axial pullout strengths were similar and significantly greater than the group 2 value; all values were significantly greater than that for group 1. Group 5 and 4 yield strengths were similar and significantly greater than the group 3, 2, and 1 values. Stiffness in group 3 was similar to group 4 and 2 values but significantly greater than the group 5 value; all values were significantly greater than that for group 1. These synthetic cancellous bone model findings suggested that tapping a 2.0-mm-diameter pilot hole when placing a 4.0-mm screw is the optimal insertion technique.

Canine cancellous bone microarchitecture after one year of high-dose bisphosphonates.

We examined the effects of one-year high-dose bisphosphonates (risedronate 0.5 mg/kg/day or alendronate 1.0 mg/kg/day) on the three-dimensional (3-D) microstructural and mechanical properties of canine cancellous bone. A high-resolution micro-CT scanner was used to scan cubic specimens produced from the first lumbar vertebrae. Microstructural properties of the specimens were calculated directly from the 3-D datasets and the mechanical properties of the specimens were determined. Our data demonstrate significant microarchitectural changes in the bisphosphonate-treated cancellous bone that was typically plate-like, denser, with thicker and more trabeculae compared with those of the controls. Consistent with architectural changes, the Young's moduli of cancellous bone increased in all three directions with the greatest increase in primary axial loading (cephalo-caudal) direction after treatment. Our results suggest a bone remodeling-adaptation mechanism stimulated by bisphosphonates that increases bone volume fraction, thickens trabeculae, changes trabeculae towards more plate-like, and increases mechanical properties. The secondary degree of anisotropy contributed significantly to the explained variance in bone strength, and the primary or tertiary degree of anisotropy improved the explanation of variances for Young's moduli, i.e., 79% of strength variances or 74-83% of modulus variances could be explained by the combined anisotropy and bone volume fraction. These significant improvements of cancellous bone architecture provide a rationale for the clinical observation that fracture risk decreased by 50% in the first year of bisphosphonate therapy with only a 5% increase in bone mineral density. We conclude that bisphosphonates enhance mechanical properties and reduce fracture risk by improving architectural anisotropy of cancellous bone 3-D microarchitecture.

The effect of hydroxyapatite on bone ingrowth into porous-coated titanium implants.

Two different groups of hydroxyapatite (HA) coated and uncoated porous titanium implants, 250-350 m and 500-700 m diameter beads, were press-fit in femoral canine cancellous bone. After 12 weeks, the dogs were euthanized and histomorphometric backscattered electron microscopy studies were carried out. Comparing HA-coated versus uncoated implants in the 250-350 m bead diameter group percentage of bone (P=0.01) and bone index (P=0.01), were higher in the HA-coated implants. Comparing HA-coated versus uncoated implants in the 500-700 m bead diameter group bone ingrowth (P=0.01) and bone depth penetration (P=0.008), were higher in HA-coated samples. It can be concluded that the HA coating was an effective method to improve bone formation and ingrowth in the porous implants. (Hip International 2002; 2: 153-7).

Validation of canine cancellous and cortical polyurethane foam bone models

SummaryThe purpose of this study was to develop standard canine cortical and cancellous polyurethane foam (PUF) bone models. Canine cancellous and cortical bone mineral densities were determined with dual-energy-x-ray absorptiometry (DXA). Polyurethane foam was cast in two densities, corresponding to the predetermined canine cancellous and cortical bone mineral densities for use as synthetic bone models. Cancellous bone screws (4.0 mm and 6.5 mm) were extracted from both canine cancellous bone segments and blocks of cancellous density PUF. Cortex bone screws (3.5 mm and 4.5 mm) were extracted from both canine cortical bone segments and blocks of cortical density PUF. There was not any difference in the cancellous screw pull-out forces between cancellous density PUF and canine cancellous bone. Cortex screw pull-out forces were significantly less for cortical density PUF than for canine cortical bone. Cancellous density PUF makes an excellent cancellous bone model for use in implant testing.

Three-dimensional culture of canine articular chondrocytes on multiple transplantable substrates

Abstract Objective To determine the effects of transplantable substrates on canine chondrocytes grown in three-dimensional culture. Animals 3 canine cadavers. Procedure Articular cartilage harvested from canine cadavers was used to obtain chondrocytes for primary culture. Subcultured chondrocytes were grown in agarose alone (AG), or in agarose on canine cancellous bone (CB), polypropylene mesh, or oxidized regenerated cellulose substrate. Cell proliferation, proteoglycan and glycosaminoglycan (GAG) production, and collagen production were assessed on days 3, 6, 10, 15 and 20. Results Chondrocytes from groups AG and CB proliferated and produced matrix over the entire 20-day study period. Group-CB chondrocytes had significantly more GAG than did chondrocytes of all other groups on days 6 (P = 0.0297) and 15 (P = 0.00272). Those of groups AG and CB contained significantly (P = 0.0235) more GAG on day 20. Chondrocytes of the polypropylene mesh group proliferated and produced matrix through day 10 in culture, but were no longer viable and had no matrix production on days 15 and 20. Regenerated cellulose appeared to be toxic to canine chondrocytes during all stages of in vitro three-dimensional culture. Conclusions Three-dimensional culture of canine chondrocytes in agarose appears to produce favorable results with respect to chondrocyte proliferation and matrix production. Canine CB appears to have beneficial effects with regard to early GAG synthesis. Polypropylene mesh and oxidized regenerated cellulose had detrimental effects on cellular proliferation and matrix production. (Am J Vet Res 1997;58:419–424)

Histomorphometry of hydroxyapatite coated and uncoated porous titanium bone implants

Two different groups of hydroxyapatite (HA) coated and uncoated porous titanium implants, 250–350 μm and 500–700 μm diameter beads, were press-fitted into femoral canine cancellous bone. After 12wks, the dogs were killed and histomorphometric backscattered electron microscopy studies were carried out. Comparing HA coated versus uncoated implants in the 250–350 μm bead diameter group, the percentage of bone ( P = 0.01) and bone index ( P = 0.01) were higher in the HA coated implants. Comparing HA coated versus uncoated implants in the 500–700 μm bead diameter group, bone ingrowth ( P = 0.01) and bone depth penetration ( P = 0.008) were higher in HA coated samples. It can be concluded that the HA coating was an effective method for improving bone formation and ingrowth in the porous implants.

Distribution of Young's modulus in the cancellous bone of the proximal canine tibia

Canine cancellous bone is used as a model for human bone in experimental orthopedic research, including models of total knee arthroplasty. Depth-force measurements produced by small-diameter indentation testing were used to derive the variation of Young's modulus over the transverse cross-sectional surface at three levels within the proximal canine tibia. At the most proximal section the presence of lateral and medial peaks of equal modulus (∼1100 MPa) was found. Modulus averages for the three resection levels revealed a trend of distally decreasing values, from 692 MPa proximally to 417 MPa distally. Average regional modulus values for the canine tibia were 50–75% higher than previously reported for the tibia of healthy young adult humans, although the local maxima were only 5–20% greater in canines.

Early strain-related changes in cultured embryonic chick tibiotarsi parallel those associated with adaptive modeling in vivo.

A model was developed for the application of cyclic mechanical loads to 17 day embryonic chick tibiotarsi in culture. A single 20 minute period of intermittent loading at 0.4 Hz, producing physiologic peak strains and strain rates, resulted in two peak strain magnitude-related responses that were previously reported in vivo: (1) a rapid increase in glucose 6-phosphate dehydrogenase activity in osteoblasts and osteocytes and (2) increased RNA synthesis, as shown by increased incorporation of [3H]uridine into extracted RNA. The RNA response was detectable 8 h following loading but was more pronounced by 24 h. Both responses were blocked by indomethacin (10(-6) M). These results demonstrate that embryonic chick bones in organ culture exhibit cellular responses to loading similar to those previously identified in adult canine cancellous bone cultures in vitro and adult avian cortical bone in vivo. These findings are consistent with a sequence of events between loading and new bone formation that includes an immediate strain magnitude-related, prostanoid-dependent increase in activity of the pentose monophosphate shunt in osteoblasts and osteocytes, followed by a similarly strain magnitude-related increase in RNA synthesis over the subsequent 24 h.

Loading-related increases in prostaglandin production in cores of adult canine cancellous bone in vitro: A role for prostacyclin in adaptive bone remodeling?

Cyclic mechanical loading sufficient to engender strains of physiologic magnitude applied to recently excised canine cancellous bone cores in vitro increased the release of prostaglandin E (PGE) and prostacyclin (PGI2, measured as its breakdown product 6-keto-PGF1 alpha), during a 15 minute loading period in which PG levels were measured in perfusing medium at 5 minute intervals. Peak production occurred in the 0-5 minute sample. Mean levels preload compared to during load were PGE, 2.66 and 3.67 ng/ml (p less than 0.002); and 6-keto-PGF1 alpha, 543 and 868 pg/ml (p less than 0.007). The elevated levels then declined to preload levels during the loading period. However, the 5-10 minute but not the 10-15 minute samples still contained levels greater than preload values. A second 15 minute period of load, 1 h following the end of the first, produced smaller increases in the levels of release that were statistically significant only for the first 0-5 minute sample during load (preload compared to load mean values, PGE, 1.09-1.66 ng/ml, p less than 0.02; 6-keto-PGF1 alpha, 401-558 pg/ml, p less than 0.04). Immunolocalization revealed PGE and 6-keto-PGF1 alpha in lining cells and 6-keto-PGF1 alpha but not PGE in osteocytes. Addition to the medium of 1 microM PGE2, approximating the concentration produced by loading, had no significant effect on the specific activity of the extractable RNA fraction labeled with [3H]uridine, whereas 1 microM PGI2 produced an increase similar to that seen previously with loading.(ABSTRACT TRUNCATED AT 250 WORDS)

Sequential histomorphometric changes in cancellous bone from ovariohysterectomized dogs

To evaluate potential pharmacologic agents for the prevention or treatment of the bone loss associated with ovarian insufficiency, a predictable animal model is needed. To assess the potential utility of the ovariohysterectomized dog as a model of this condition, we characterized the sequential histomorphometric changes in canine cancellous bone in response to the loss of ovarian function. A group of 25 adult beagle dogs were ovariohysterectomized and terminated at 1, 3, 6, and 10 months following surgery. Iliac biopsies were performed following double-fluorochrome labeling at the time of surgery and at termination. Static and dynamic histomorphometry was performed on undecalcified sections. By 3 months postovariohysterectomy, there was activation of cancellous bone remodeling as indicated by significant increases in mineralizing surface and bone formation rate. Increases in osteoid surface, mineralizing surface, and bone formation rate were also apparent at 1 month postovariohysterectomy, and although not statistically significant, these trends suggest the skeletal response to acute loss of ovarian function was rapid. This increase in bone remodeling was transient. By 6 months, mineralizing surface and bone formation rate were depressed below presurgical levels. In addition to a reduction in bone formation, a reduction in osteoblast function characterized by reduced labeling of osteoid and a disproportionate increase in eroded surface also occurred. By 10 months postovariohysterectomy, cancellous bone remodeling was not significantly different from presurgical levels. At no time was a significant reduction in bone volume detected. These data suggest that the changes in cancellous bone remodeling in the ovariohysterectomized dog are a series of transient phenomena.(ABSTRACT TRUNCATED AT 250 WORDS)

Elastic moduli, yield stress, and ultimate stress of cancellous bone in the canine proximal femur

Elastic moduli, yield stress and ultimate compressive stress were determined for cancellous bone from the femoral head and neck regions of the canine femur. Unconfined compression tests were performed on 5 mm cubic samples which were cut from two femurs. Elastic moduli were measured in three orthogonal directions, and the yield stress and ultimate stress were measured along the proximal-distal axis. The results from this investigation support previous assumptions that the mechanical behavior of canine cancellous bone is qualitatively similar to human cancellous bone. The canine cancellous bone was observed to be anisotropic in elastic modulus. For two thirds of the cubic specimens tested, the elastic modulus was largest in the load-bearing, proximal-distal direction. A linear relationship between yield stress and elastic modulus was observed for canine bone, as is typical of human bone. A similar linear relationship between ultimate stress and elastic modulus was observed. Thus, for canine bone as well as for human bone, failure appears to be governed by a strain level which is position independent. The yield strain of 0.0259 and ultimate strain of 0.0288 for canine bone were both less than the yield strain of 0.0395 reported for human bone.

Resorption characteristics of bone and bone substitutes

Resorption of ninety intramuscular implants of different types of bone and bone substitutes were studied radiographically in twenty-two adult mongrel dogs. On the basis of mean resorption time, the implants were resorbed in the following order: (1) plaster of Paris, (2) autogenous cancellous bone, (3) cathode-ray-sterilized canine cancellous bone, (4) cathode-ray-sterilized human cancellous bone, (5) homologous cancellous bone, (6) fetal bovine bone, (7) bovine cancellous bone, (8) freeze-dried cancellous bone, (9) collapatite, (10) anorganic bone, and (11) polyurethane foam. The significance of these findings and their possible correlation with other clinical studies are discussed.