ABSTRACT
Pleiotrophin (PTN) was found to have potent effects on regulation of osteoblast recruitment, proliferation and differentiation. The present study examined the long-term effects of targeted PTN over-expression on bone development and repair in a transgenic mouse model. Femurs and tibiae from the PTN transgenic mice and the wild type mice at age 1, 2, 4, 6, 12 and 24 months were collected, and examined by radiography, peripheral quantitative computed tomography (pQCT), histology and mechanical testing. Age-matched PTN and the control mice received a standardized femoral fracture, followed by regular x-rays and sacrificed at day 16 post-fracture for histology examination. A cortical hole was drilled on the tibiae of age-matched PTN and wild type mice, collagen sponge with either saline, 100 ng of rhBMP-2 or rhPTN was implanted in the holes, and animals were sacrificed 10 days later, subject to pQCT and histology examinations. During early stages of bone development, the PTN mice had advanced bone growth in length and maturation, but the difference diminished in later life. The fracture healing was impaired in the PTN mice, and there was delayed callus formation and remodelling. The cortical holes treated with BMP-2 in the PTN mice had significantly less trabecular bone formation. The current study confirmed that the targeted PTN over-expression in mouse bone has moderate enhancing effects on early bone development; but the bones become brittle in later life. Fracture healing was impaired in the adult PTN mice and this may be due to inhibitory effects of PTN over-expression on BMP-2 mediated bone induction.
Subject(s)
Bone Development/physiology , Bone Regeneration/physiology , Carrier Proteins/metabolism , Cytokines/metabolism , Fracture Healing/physiology , Animals , Bone Development/drug effects , Bone Morphogenetic Protein 2 , Bone Morphogenetic Proteins/pharmacology , Bone Regeneration/drug effects , Carrier Proteins/genetics , Compressive Strength , Cytokines/genetics , Disease Models, Animal , Femur/metabolism , Femur/pathology , Fracture Healing/drug effects , Humans , Male , Mice , Mice, Inbred Strains , Mice, Transgenic , Recombinant Proteins , Tibia/drug effects , Tibia/metabolism , Tibia/pathology , Transforming Growth Factor beta/pharmacologyABSTRACT
In this study, the fatigue strengths of acrylic cement prepared by various commercially available reduced pressure mixing systems were compared with the fatigue strength of cement mixed by hand (control) under atmospheric conditions. The following observations were made from this investigation. The mean fatigue strength of reduced pressure mixed acrylic bone cement is double that of cement mixed by hand using an open bowl, 11,354+/-6,441 cycles to failure for reduced pressure mixing in comparison with 5,938+/-3,199 cycles for mixing under atmospheric conditions. However, the variability in mean fatigue strengths of reduced pressure mixed bone cement is greater for some mixing devices. The variation in fatigue strengths for the different mixing techniques is explained by the different porosity distributions. The design of the reduced pressure mixing system and the technique employed during mixing strongly contribute to the porosity distribution within the acrylic bone cement. The level of reduced pressure applied during cement mixing has an effect on the fatigue strength of bone cement, but the mixing mechanism is significantly more influential.
Subject(s)
Biocompatible Materials , Bone Cements , Materials Testing , PorosityABSTRACT
At 5 and 15 weeks post-surgery, biomechanical and histological analyses of cancellous bone defects filled with the bovine trabecular bone matrix (BBM) and hydroxyapatite (Hap) particulates of dimensions 106-150 microm were investigated. It was observed that at 5 weeks post-surgery the stiffness properties of the BBM filled defects were significantly higher than those observed in the Hap filled defects (p < 0.01) but comparable to those recorded in intact cancellous bone from the same anatomical position. Histologically, no significant differences were observed in the percentage of new bone contact with the particles. The biomechanical properties of the Hap filled defects mirrored those in intact cancellous bone only at 15 weeks post-surgery. BBM particles thus appeared to accelerate the early healing of osteotomies. It is therefore suggested that particles of this bioceramic be the subject of intense research for more usage in both periodontal osseous defects and orthopaedic fractures.
Subject(s)
Bone Remodeling , Bone and Bones , Animals , Biocompatible Materials , Cattle , Hydroxyapatites , X-Ray DiffractionABSTRACT
This paper reports the effects of a synthetic bone substitute and bone allograft on cortical bone repair in an experimental model. To test the hypothesis that bovine trabecular bone matrix, BBM, can enhance the repair rate of cortical bone, osteotomies were created in the rabbit fibula and filled with either allograft or BBM particulates or left empty as controls. At five weeks post-surgery, mechanical tests and histological evaluations were performed. No significant differences were observed in the mechanical properties of the healing bone in the three animal groups (n=6). Histologically, the medullary cavity was obstructed and the cross-sectional area ratio of the osteotomies to intact bone was approximately 3 : 1. Highly significant area differences were observed between the intact bone group and both the BBM and the allograft groups (p< 0.001). At the junction between the original bone and the newly formed bone, both woven and lamellar bone microstructures were prevalent. However, in the BBM filled defects, the woven bone microstructure was not ostentatious. It is concluded that failure to demonstrate significantly differences between the treatments were due to the small sample sizes and or the efficacy of the tensile analysis.
