Novel methodology for assessing biomaterial–biofluid interaction in cancellous bone

Vertebral balloon kyphoplasty versus vertebral body stenting in non-osteoporotic vertebral compression fractures at the thoracolumbar junction: a comparative radiological study and finite element analysis (BONEXP study)

OBJECTIVE

To compare radiologically balloon kyphoplasty (BKP) and vertebral compression fracture (VCF) expansion and corroborate with a finite element (FE) analysis. The principle of BKP is to stabilize VCF by restoring vertebral body anatomy using bone expansion and cement filling. More recently, vertebral body stenting (VBS) has been developed to reduce the loss of vertebral height observed after balloon deflation.

METHODS

A retrospective, monocentric and continuous study of 60 non-osteoporotic fractures of the thoracolumbar junction treated by vertebral bone expansion was carried out over three years. The main endpoint was radiological correction of vertebral kyphosis (VK) at 3 months. The other studied parameters were vertebral height, index of Farcy, index of Beck, cement leakages and their location. A FE model was developed to analyze effects linked to the stent during cement injection, specifically throughout the risk of cement leakage evaluation.

RESULTS

After three months, average reduction of VK was 4.73° ± 4.8° after BKP, and 4.63° ± 2.7° after VBS. There was no difference between the two techniques, but cement leakage was significantly greater with BKP (41.7%) than with VBS (4.2%). FE analysis showed substantial changes of the cement flow orientation in the presence of a stent.

CONCLUSION

BKP and VBS offer comparable expansion with no added value of VBS in non-osteoporotic VCF reduction. VBS technique appears to prevent cement leakage due to its mesh architecture hindering the leaking process. In counterpart, such balloon expansion is likely to require higher pressure to deploy the stent. This could be an important parameter to take into account in young patients with high bone density.

Formulating injectable pastes of porous calcium phosphate glass microspheres for bone regeneration applications

Current trends in regenerative medicine treatments for bone repair applications focus on cell-based therapies. These aim to deliver the treatment via a minimally invasive injection to reduce patient trauma and to improve efficacy. This paper describes the injectability of porous calcium phosphate glass microspheres to be used for bone repair based on their formulation, rheology and flow behavior. The use of excipients (xanthan gum, methyl cellulose and carboxyl methyl cellulose) were investigated to improve flow performance. Based on our results, the flow characteristics of the glass microsphere pastes vary according to particle size, surface area, and solid to liquid ratio, as well as the concentration of viscosity modifiers used. The optimal flow characteristics of calcium phosphate glass microsphere pastes was found to contain 40 mg/mL of xanthan gum which increased viscosity whilst providing elastic properties (∼29,000 Pa) at shear rates that mirror the injection process and the resting period post injection, preventing the glass microspheres from both damage and dispersion. It was established that a base formulation must contain 1 g of glass microspheres (60-125 μm in size) per 1 mL of cell culture media, or 0.48 g of glass microspheres of sizes between 125 and 200 μm. Furthermore, the glass microsphere formulations with xanthan gum were readily injectable via a syringe-needle system (3-20 mL, 18G and 14G needles), and have the potential to be utilized as a cell (or other biologics) delivery vehicle for bone regeneration applications.

A Review of PMMA Bone Cement and Intra-Cardiac Embolism

Percutaneous vertebroplasty procedure is of major importance, given the significantly increasing aging population and the higher number of orthopedic procedures related to vertebral compression fractures. Vertebroplasty is a complex technique involving the injection of polymethylmethacrylate (PMMA) into the compressed vertebral body for mechanical stabilization of the fracture. Our understanding and ability to modify these mechanisms through alterations in cement material is rapidly evolving. However, the rate of cardiac complications secondary to PMMA injection and subsequent cement leakage has increased with time. The following review considers the main effects of PMMA bone cement on the heart, and the extent of influence of the materials on cardiac embolism. Clinically, cement leakage results in life-threatening cardiac injury. The convolution of this outcome through an appropriate balance of complex material properties is highlighted via clinical case reports.