Ceramic cement as a potential stand-alone treatment for bone fractures: An in vitro study of ceramic-bone composites.

BACKGROUND: A vertebral burst fracture (VBF) treated with vertebroplasty using a ceramic cement consists of four regions; native bone fragments, native ceramic cement, ceramic cement-trabecular bone (ceramic-bone) composite and ceramic-bone interface. Although the mechanical properties of native bone and native ceramic cements have been well investigated, the mechanical properties of ceramic-bone composite and ceramic-bone interface remain unknown. Therefore, the aim of this study was to determine the mechanical properties of ceramic-bone composites and ceramic-bone interfaces. Two types of ceramic cement, calcium aluminate (CAC) with (w/F) and without (wo/F) fiber reinforcement, were investigated. METHODS: Ceramic-bone composite (Full, wo/F and w/F) and ceramic-bone interface (Fract, wo/F and w/F) groups were tested to determine their compressive and tensile properties. While a continuous bone cylinder was used for samples in the Full groups, each bone cylinder for the samples in the Fract groups contained a 3mm geometrical discontinuity to mimic the fracture gaps in VBFs. Two Cement groups (wo/F and w/F) and a Bone group were included in the study as controls. Micro-CT images were used to determine the bone morphological parameters, as potential predictors of the mechanical properties of Full and Fract groups. RESULTS: The compressive strengths of Full and Fract groups were substantially lower than native CAC, but higher than bone. The tensile strength of the Full group was equal to bone, while the tensile strength of the Fract group was equivalent to CAC. Variable relationships between the bone morphological parameters and mechanical properties of Full and Fract groups were observed. Fiber reinforcement at an injectable level had a minimal influence on the mechanical properties. CONCLUSIONS: CAC augmentation does not provide adequate stabilization of bone fragments. The interface between bone and cement represents a weak point. The effect of cement augmentation cannot be predicted by bone morphological properties.

In silico investigation of vertebroplasty as a stand-alone treatment for vertebral burst fractures.

BACKGROUND: The use of percutaneous vertebroplasty as a stand-alone treatment for stable vertebral burst fractures has been investigated in vitro and in clinical studies. These studies present inconsistent results on the mechanical response of vertebroplasty-treated burst fractures. In addition, observations of the loss of sagittal alignment after vertebroplasty raise questions on the applicability of vertebroplasty for burst fractures. Therefore, the aim of this study was to investigate the mechanical stability of burst fractures after stand-alone treatment by vertebroplasty. METHODS: Finite element simulations were performed with models generated from two laboratory-induced burst fractures in human thoracolumbar specimens. The burst fracture models were virtually injected with various cement volumes using a unipedicular or bipedicular approach. The models were subjected to four individual loads (compression, lateral bending, extension and torsion) and a multi-axial load case in the physiological range. FINDINGS: All treated burst fractures showed improvements in stiffness and a reduction in inter-fragmentary displacements, thus potentially providing a suitable mechanical environment for fracture healing. However, large volumes of the trabecular bone (<43%), cement (<53%) and bone-cement composite (<58%) were predicted to experience strain levels exceeding the yield point. While damage was not specifically modeled, this implies a potential collapse of the treated vertebra due to local failure. INTERPRETATION: To improve the primary stability and to prevent the collapse of treated burst fractures, the use of posterior instrumentation is suggested as an adjunct to vertebroplasty.

The effect of water on the mechanical properties of soluble and insoluble ceramic cements.

Ceramic cements are good candidates for the stabilization of fractured bone due to their potential ease of application and biological advantages. New formulations of ceramic cements have been tested for their mechanical properties, including strength, stiffness, toughness and durability. The changes in the mechanical properties of a soluble cement (calcium sulfate) upon water-saturation (saturation) was reported in our previous study, highlighting the need to test ceramic cements using saturated samples. It is not clear if the changes in the mechanical properties of ceramic cements are exclusive to soluble cements. Therefore the aim of the present study was to observe the changes in the mechanical properties of soluble and insoluble ceramic cements upon saturation. A cement with high solubility (calcium sulfate dihydrate, CSD) and a cement with low solubility (dicalcium phosphate dihydrate, DCPD) were tested. Three-point bending tests were performed on four different groups of: saturated CSD, non-saturated CSD, saturated DCPD, and non-saturated DCPD samples. X-ray diffraction analysis and scanning electron microscopy were also performed on a sample from each group. Flexural strength, effective flexural modulus and flexural strain at maximum stress, lattice volume, and crystal sizes and shape were compared, independently, between saturated and non-saturated groups of CSD and DCPD. Although material dissolution did not occur in all cases, all calculated mechanical properties decreased significantly in both CSD and DCPD upon saturation. The results indicate that the reductions in the mechanical properties of saturated ceramic cements are not dependent on the solubility of a ceramic cement. The outcome raised the importance of testing any implantable ceramic cements in saturated condition to estimate its in vivo mechanical properties.

The compressive modulus and strength of saturated calcium sulphate dihydrate cements: implications for testing standards.

Calcium sulphate-based bone cement is a bone filler with proven biological advantages including biodegradability, biocompatibility and osteoconductivity. Mechanical properties of such brittle ceramic cements are frequently determined using the testing standard designed for ductile acrylic cements. The aims of the study were (1) to validate the suitability of this common testing protocol using saturated calcium sulphate dihydrate (CSD), and (2) to compare the strength and effective modulus of non-saturated and saturated CSD, in order to determine the changes in the mechanical behavior of CSD upon saturation. Unconfined compression tests to failure were performed on 190 cylindrical CSD samples. The samples were divided into four groups having different saturation levels (saturated, non-saturated) and end conditions (capped and non-capped). Two effective moduli were calculated per sample, based on the deformations measured using the machine platens and a sample-mounted extensometer. The effective moduli of non-saturated groups were found to be independent of the end conditions. The saturated and capped group showed no difference in the effective moduli derived from different measurement methods, while the saturated and non-capped group showed a significant difference between the machine platen- and extensometer-derived moduli. Strength and modulus values were significantly lower for saturated samples. It was assumed that the existence of water in saturated CSD alters the mechanical response of the material due to the changes in chemical and physical behaviors. These factors are considered to play important roles to decrease the shear strength of CSD. It was proposed that the reduction in CSD shear strength evokes local deformation at the platen-sample boundary, affecting the strength and effective moduli derived from the experiments. The results of this study highlighted the importance of appropriate and consistent testing methods when determining the mechanical properties of saturated ceramic cements.