[Show abstract][Hide abstract] ABSTRACT: The aim of the study was to use a computational and experimental approach to evaluate, compare and predict the ability of calcium phosphate (CaP) and poly (methyl methacrylate) (PMMA) augmentation cements to restore mechanical stability to traumatically fractured vertebrae, following a vertebroplasty procedure. Traumatic fractures (n = 17) were generated in a series of porcine vertebrae using a drop-weight method. The fractured vertebrae were imaged using μCT and tested under axial compression. Twelve of the fractured vertebrae were randomly selected to undergo a vertebroplasty procedure using either a PMMA (n = 6) or a CaP cement variation (n = 6). The specimens were imaged using μCT and re-tested. Finite element models of the fractured and augmented vertebrae were generated from the μCT data and used to compare the effect of fracture void fill with augmented specimen stiffness. Significant increases (p < 0.05) in failure load were found for both of the augmented specimen groups compared to the fractured group. The experimental and computational results indicated that neither the CaP cement nor PMMA cement could completely restore the vertebral mechanical behavior to the intact level. The effectiveness of the procedure appeared to be more influenced by the volume of fracture filled rather than by the mechanical properties of the cement itself.
[Show abstract][Hide abstract] ABSTRACT: The study aim was to develop and apply an experimental technique to determine the biomechanical effect of polymethylmethacrylate (PMMA) and calcium phosphate (CaP) cement on the stiffness and strength of augmented vertebrae following traumatic fracture. Twelve burst type fractures were generated in porcine three-vertebra segments. The specimens were randomly split into two groups (n=6), imaged using microCT and tested under axial loading. The two groups of fractured specimens underwent a vertebroplasty procedure, one group was augmented with CaP cement designed and developed at Queen's University Belfast. The other group was augmented with PMMA cement (WHW Plastics, Hull, UK). The specimens were imaged and re-tested . An intact single vertebra specimen group (n=12) was also imaged and tested under axial loading. A significant decrease (p<0.01) was found between the stiffness of the fractured and intact groups, demonstrating that the fractures generated were sufficiently severe, to adversely affect mechanical behaviour. Significant increase (p<0.01) in failure load was found for the specimen group augmented with the PMMA cement compared to the pre-augmentation group, conversely, no significant increase (p<0.01) was found in the failure load of the specimens augmented with CaP cement, this is attributed to the significantly (p<0.05) lower volume of CaP cement that was successfully injected into the fracture, compared to the PMMA cement. The effect of the percentage of cement fracture fill, cement modulus on the specimen stiffness and ultimate failure load could be investigated further by using the methods developed within this study to test a more injectable CaP cement.
Journal of Biomechanics 12/2012; 46(4). DOI:10.1016/j.jbiomech.2012.11.036 · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The aim of this study was to examine the potential of incorporating bovine fibres as a means of reinforcing a typically brittle apatite calcium phosphate cement for vertebroplasty. Type I collagen derived from bovine Achilles tendon was ground cryogenically to produce an average fibre length of 0.96±0.55mm and manually mixed into the powder phase of an apatite-based cement at 1, 3 or 5wt.%. Fibre addition of up to 5wt.% had a significant effect (P⩽0.001) on the fracture toughness, which was increased by 172%. Adding ⩽1wt.% bovine collagen fibres did not compromise the compressive properties significantly, however, a decrease of 39-53% was demonstrated at ⩾3wt.% fibre loading. Adding bovine collagen to the calcium phosphate cement reduced the initial and final setting times to satisfy the clinical requirements stated for vertebroplasty. The cement viscosity increased in a linear manner (R(2)=0.975) with increased loading of collagen fibres, such that the injectability was found to be reduced by 83% at 5wt.% collagen loading. This study suggests for the first time the potential application of a collagen-reinforced calcium phosphate cement as a viable option in the treatment of vertebral fractures, however, issues surrounding efficacious cement delivery need to be addressed.
[Show abstract][Hide abstract] ABSTRACT: Calcium phosphate cements have the potential to be successful in minimally invasive surgical techniques, like that of vertebroplasty, due to their ability to be injected into a specific bone cavity. These bone cements set to produce a material similar to that of the natural mineral component in bone. Due to the ceramic nature of these materials they are highly brittle and it has been found that they are difficult to inject. This study was carried out to determine the factors that have the greatest effect on the mechanical and handling properties of an apatitic calcium phosphate cement with the use of a Design of Experiments (DoE) approach. The properties of the cement were predominantly influenced by the liquid:powder ratio and weight percent of di-sodium hydrogen phosphate within the liquid phase. An optimum cement composition was hypothesised and tested. The mechanical properties of the optimised cement were within the clinical range for vertebroplasty, however, the handling properties still require improvement.
Journal of Materials Science Materials in Medicine 08/2010; 21(8):2299-305. DOI:10.1007/s10856-009-3977-9 · 2.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The strategic incorporation of bioresorbable polymeric additives to calcium-deficient hydroxyapatite cement may provide short-term structural reinforcement and modify the modulus to closer match bone. The longer-term resorption properties may also be improved, creating pathways for bone in-growth. The aim of this study was to investigate the resorption process of a calcium phosphate cement system containing either in polyglycolic acid tri-methylene carbonate particles or polyglycolic acid fibres. This was achieved by in vitro aging in physiological conditions (phosphate buffered solution at 37 degrees C) over 12 weeks. The unreinforced CPC exhibited an increase in compressive strength at 12 weeks, however catastrophic failure was observed above a critical loading. The fracture behaviour of cement was improved by the incorporation of PGA fibres; the cement retained its cohesive structure after critical loading. Gravimetric analysis and scanning electron microscopy showed a large proportion of the fibres had resorbed after 12 weeks allowing for the increased cement porosity, which could facilitate cell infiltration and faster integration of natural bone. Incorporating the particulate additives in the cement did not provide any mechanism for mechanical property augmentation or did not demonstrate any appreciable level of resorption after 12 weeks.
Journal of Materials Science Materials in Medicine 03/2010; 21(8):2263-70. DOI:10.1007/s10856-010-4021-9 · 2.59 Impact Factor