Assessing the advantages of CFR-PEEK over titanium spinal stabilization implants in proton therapy-a phantom study.

High-density materials, such as titanium, used for spinal stabilization, introduces several critical issues in proton therapy (PT). Artefacts affect both contouring and dose calculation. Subsequently, artefacts need to be corrected which is a time-consuming process. Besides, titanium causes proton interactions that are unaccounted for in dose calculation. The result is a suboptimal treatment plan, and indeed decreased local controls have been reported for these patients. Carbon fiber reinforced polyetheretherketone (CFR-PEEK) implant material, which is of low density, potentially solves these issues. For this study, we designed a unique phantom to compare the effects of titanium and CFR-PEEK implants in PT. The phantom contains four interchangeable spinal inserts representing a native spine, and three different spinal stabilizations consisting of titanium only, CFR-PEEK only, and a combination of titanium and CFR-PEEK. All phantom scenarios received the standard treatment workup. Two planning approaches were investigated: a single field plan and a multi-field optimized plan with spinal cord sparing. For both plans we analyzed the following aspects: total volume of artefacts on CT images, time required for artefact correction, effect of planning CT correction on dose calculation, plan robustness to range and set up uncertainties, and finally the discrepancy between the calculated dose and the delivered dose with Gafchromic® film. The CFR-PEEK implant had a 90% reduction of artefacts on CT images and subsequently severely reduced the time for artefact correction with respect to the titanium-only implant. Furthermore, the CFR-PEEK as opposed to titanium did not influence the robustness of the plan. Finally, the titanium implants led to hardware-related discrepancies between the planned and the measured dose while the CFR-PEEK implant showed good agreement. As opposed to titanium, CFR-PEEK has none to minor effects on PT. The use of CFR-PEEK is expected to optimize treatment and possibly improve outcomes for patients that require spinal stabilization.

Biomechanical evaluation of a new augmentation method for enhanced screw fixation in osteoporotic proximal femoral fractures.

A biomechanical investigation on eight pairs of human cadaver proximal femurs was performed to evaluate the impact of a new augmentation method on the internal fixation of osteoporotic proximal femur fractures. The study focused on enhancing implant purchase to reduce the incidence of implant cut-out in osteoporotic bone. In a left-right comparison, a conventional hip screw fixation (control) was compared to the new cement augmentation method. After bone bed preparation through high pressure irrigation to remove fat, blood, and bone debris, the bones were augmented with low viscosity polymethylmethacrylate (PMMA) cement. Step-wise fatigue testing was performed by cyclically loading the femoral heads in a physiological manner, beginning at 1,500 N and increasing 500 N every 5,000 cycles to 4,000 N, and continuously monitoring head displacement. Failure was defined as >5.0 mm head displacement. The head displacement at 2,000 N was significantly smaller (p=0.018) for the augmented group as compared to the conventionally treated bones (0.09+/-0.01 mm vs. 0.90+/-0.32 mm; mean+/-SEM). The displacement rate at the second load step was significantly higher (p=0.018) for the conventionally treated bones as compared to the augmented ones. All of the nonaugmented specimens failed during testing, where 50% of the augmented specimens did not fail. The promising results of these experiments suggest that this new standardized irrigation/augmentation method enhances the implant anchorage and offers a potential solution to the problem of implant cut-out in osteoporotic metaphyseal bone.

Augmentation of implant purchase with bone cements: an in vitro study of injectability and dough distribution.

Vertebroplasty is widely used to treat (augment) osteoporotic fractures of the spine. This technique--with or without metallic implants--might have more widespread indications, if the mechanics of the injection and distribution of the cement dough through cannulated instruments and implants were better understood. This study was performed to investigate injectability of calcium phosphate and acrylic bone cements through implant prototypes, which featured different perforated sleeve designs. Using a custom-made capillary rheometer, the forces needed to inject 10 mL of the cement dough through standard cannulas were measured in the first series of experiments. In the second series, plastic sleeves were attached to the rheometer, simulating the implant. In both series, the dough was injected into ambient laboratory atmosphere, and in the second series, cement distribution was analyzed by means of an optical system. Injection of cement dough through the cannulas required forces between 50 and 400 N in the case of acrylic cements and between 40 and 500 N in case of the calcium phosphate cements. Using different sleeves did not have a significant influence on the distribution of the cement dough around the sleeve. The amount of cement dough injected was reduced when a perforated implant was attached to the cannula. More material was delivered through the proximal holes of the implant, leading to a V-shaped distribution of the cement dough. Among topics to be investigated in future studies is determination of the injectability of cement dough into trabecular bone or bone-like structures.

Augmentation of osteoporotic bone: effect of pulsed jet-lavage on injection forces, cement distribution, and push-out strength of implants.

Demographic change in the population leads to higher incidence of fragility fractures. Fracture fixation with standard implants may lead to implant cut-out due to reduced purchase. Augmentation of the bone stock with bone cements might overcome this problem. However, cancellous bone infiltration with the viscous cement dough reveals problems of fat embolism or high pressures during application of the cement. This study investigates the improved quality of bovine cancellous bone augmentation when pulsed jet-lavage is used for fat and marrow removal. Parameters such as injection forces, cement dough distribution through cannulated implants and mechanical strength of the fixation were applied for quantification. Injection of 5 mL of acrylic bone cement required significantly lower forces in the lavaged as compared to the untreated bone (50 N vs. > 300 N). Cement distribution was much more homogeneous and push-out forces significantly higher in the pretreated bone group (8.33 +/- 1.41 kN vs. 1.66 +/- 0.63 kN). The application of pulsed jet-lavage for fat removal prior to acrylic cement augmentation led to much more controlled outcomes of the augmentation. This seems to be a relevant step towards safe and efficient injection of bone cements into cancellous bone structures.

Intra-articular calcium phosphate cement: Its fate and impact on joint tissues in a rabbit model.

Clinical application of injectable ceramic cement in comminuted fractures revealed penetration of the viscous paste into the joint space. Not much is known on the fate of this cement and its influence on articular tissues. The purpose of this experimental study was to assess these unknown alterations of joint tissues after intra-articular injection of cement in a rabbit knee. Observation periods were from 1 week up to 24 months, with three rabbits per group. Norian SRS cement was injected into one knee joint, the contralateral side receiving the same volume of Ringers' solution. Light microscopic evaluation of histologic sections was performed, investigating the appearance of the cement, inflammatory reactions, and degenerative changes of the articular surface. No signs of pronounced acute or chronic inflammation were visible. The injected cement was mainly found as a single particle, anterior to the cruciate ligaments. It became surrounded by synovial tissues within 4 weeks and showed signs of superficial resorption. In some specimens, bone formation was seen around the cement. Degeneration of the articular surface showed no differences between experimental and control side, and no changes over time became apparent. No major degenerative changes were induced by the injected cement. The prolonged presence of cement still seems to make it advisable to remove radiologically visible amounts from the joint space.

Resorption patterns of calcium-phosphate cements in bone.

Two calcium phosphate cements, one monophasic and the other biphasic, have been used as bone void filler in a sheep model. The cements were injected into a slot defect in the proximal tibia and into a cylindrical defect in the distal femur. In this study, we focused on the resorption pattern of the two cement formulations and the subsequent biologic reaction. Bone remodeling occurred synchronously with the resorption of the implant material in a creeping substitution process. Cracks and pores in the monophasic cement were filled with osseous tissues. The biphasic cement showed faster resorption of the matrix. The more slowly resorbing granules were surrounded by newly grown bone, thus providing an inverse scaffold for cancellous bone regeneration. In highly loaded areas, the long-term support function of the fixation appears to be critical. Because cortical bridging of the defects was seen in only one case, it can be concluded that calcium-phosphate cements are preferentially suitable as cancellous bone substitute materials.

Development of an in vivo experimental model for percutaneous vertebroplasty in sheep.

INTRODUCTION: Several studies have described 'open' approach techniques for cementation of sheep and goat vertebrae; however, no percutaneous technique has been developed so far for use in non-primates. The aim of this study was to develop an animal model for percutaneous vertebroplasty under clinical conditions. METHODS: In a pilot study with dissected cadaveric ovine vertebrae, the technique and instruments as well as the optimal needle position were determined. In an in vivo animal study using 33 lumbar vertebrae of 11 sheep, a percutaneous vertebroplasty was performed under general anaesthesia. Needle position and cement volume were evaluated from high resolution, quantitative computed tomography imaging. RESULTS: The percutaneous technique for vertebroplasty was applicable to the vertebral bodies (L1 to L5) of the ovine lumbar spine without any related adverse effects for the animals. The procedure showed a steep learning curve represented by the reduction of the distance between the actual and planned needle positioning (7.2 mm to 3.7 mm; median value) and shorter surgery times (21.3 min to 15.0 min, average) with progression of the study. CONCLUSION: The described technique is feasible and repeatable under clinical conditions. This is the first percutaneous vertebroplasty technique for non-primates and we conclude that the sheep is a valid animal model to investigate the effects of cement augmentation in vivo.

[Solid body augmentation for comminuted calcaneal fractures : development and biomechanical testing of a hybrid osteosynthesis technique]. / Festkörperaugmentation bei Kalkaneustrümmerfrakturen : Entwicklung und biomechanische Testung einer Hybridosteosynthesetechnik.

BACKGROUND: Comminuted calcaneal fractures are a consequence of high impact trauma to the foot. Stable fixation and anatomically correct repositioning of the joint surfaces are often a problem. To improve fracture treatment, surgical techniques in combination with new augmentation materials have been tested. METHODS: This study presents a new concept of osteosynthesis of complex calcaneal fractures in combination with an alternative augmentation technique. Solid body augmentation was developed and mechanically tested against standard techniques. The solid body was used for augmentation of a central fracture void in combination with conventional plating. RESULTS: The results show a statistically significant higher stability of the new hybrid osteosynthesis concept against conventional plating techniques under in-vitro conditions. CONCLUSIONS: This work investigated a new concept of internal support of multifragmentary calcaneal fractures. Augmentation of defect voids in the calcaneus with a mechanically stable solid body implant in combination with stable screw anchorage in this implant leads to a higher stability compared to plate-fixation and augmentation with cancellous bone under in-vitro conditions.

Mechanical characterisation of a bone defect model filled with ceramic cements.

Ceramic bone substitute materials are often used to fill defects in comminuted articular fractures. In an in vivo study [1], calcium phosphate cements have been injected into highly loaded slot defects in the proximal tibial metaphysis. During healing, cracks were formed mostly in the proximal anterior aspect of the implanted cement and wedge-like gaps formed between the tibial plateau and the cement. Mechanical ex vivo tests were done to investigate the mechanical competence of the bone cement in such a defect situation. Entirely filled defects were loaded with up to 4.5 kN until they failed. Cyclic loading of the proximal tibiae caused micro fragmentation of the cement after 1000 cycles at 1.5-2.0 kN load. This aspect was comparable to cement fragmentation observed in vivo. Large defects in highly loaded areas should therefore additionally be stabilised with metallic implants. The ceramic cement can only be used as a filler material, which can be replaced by new bone upon resorption.

Topographical characterization and microstructural interface analysis of vacuum-plasma-sprayed titanium and hydroxyapatite coatings on carbon fibre-reinforced poly(etheretherketone).

In the present study, topographical characterization and microstructural interface analysis of vacuum-plasma-sprayed titanium and hydroxyapatite (HA) coatings on carbon fibre-reinforced polyetheretherketone (CF/PEEK) was performed. VPS-Ti coatings with high roughness values (Ra=28.29+/-3.07 microm, Rz=145.35+/-9.88 microm) were obtained. On this titanium, intermediate layer HA coatings of various thicknesses were produced. With increasing coating thickness, roughness values of the HA coatings decreased. A high increase of profile length ratio, Lr, of the VPS-Ti coatings (Lr=1.45) compared to the grit-blasted CF/PEEK substrate (Lr=1.08) was observed. Increasing the HA coating thickness resulted in a reduction of the Lr values similar to the roughness values. Fractal analysis of the obtained roughness profiles revealed that the VPS-Ti coatings showed the highest fractal dimension of D=1.34+/-0.02. Fractal dimension dropped to a value of 1.23-1.25 for all HA coatings. No physical deterioration of the CF/PEEK substrate was observed, indicating that substrate drying and the used VPS process parameter led to the desired coatings on the composite material. Cross-section analysis revealed a good interlocking between the titanium intermediate layer and the PEEK substrate. It is therefore assumed that this interlocking results in suitable mechanical adhesive strength. From the results obtained in this study it is concluded that VPS is a suitable method for manufacturing HA coatings on carbon fibre-reinforced PEEK implant materials.