R. Aquarius

Frictional and bone ingrowth properties of engineered surface topographies produced by electron beam technology

BackgroundElectron beam melting (E-beam) is a new technology to produce 3-dimensional surface topographies for cementless orthopedic implants.MethodsThe friction coefficients of two newly developed E-beam produced surface topographies were in vitro compared with sandblasted E-beam and titanium plasma sprayed controls. Bone ingrowth (direct bone–implant contact) was determined by implanting the samples in the femoral condyles of 6 goats for a period of 6xa0weeks.ResultsFriction coefficients of the new structures were comparable to the titanium plasma sprayed control. The direct bone–implant contact was 23.9 and 24.5% for the new surface structures. Bone–implant contact of the sandblasted and titanium plasma sprayed control was 18.2 and 25.5%, respectively.ConclusionsThe frictional and bone ingrowth properties of the E-beam produced surface structures are similar to the plasma-sprayed control. However, since the maximal bone ingrowth had not been reached for the E-beam structures during the relatively short-term period, longer-term follow-up studies are needed to assess whether the E-beam structures lead to a better long-term performance than surfaces currently in use, such as titanium plasma spray coating.

The fracture risk of adjacent vertebrae is increased by the changed loading direction after a wedge fracture

Study Design. In vitro biomechanical study. Objective. To measure the effect that off-axis vertebral loading has on the stiffness and failure load of vertebrae. Summary of Background Data. Adjacent level vertebral fractures not only are common in patients who received a vertebroplasty treatment but also occur in patients with conservatively treated wedge fractures. The wedge-like deformity, which is present in both groups, changes the spinal alignment. The load of vertebrae adjacent to the fractured vertebra will change from perpendicular to the endplate to a more shearing, off-axis, load. This change may induce a higher fracture risk for vertebrae adjacent to wedge-like deformed vertebrae. Methods. Twenty vertebrae, harvested from one osteopenic cadaver spine and three osteoporotic cadaver spines, were loaded until failure. The vertebrae were loaded either perpendicular to the upper endplate, representing vertebrae in a spine without wedge fractures (0° group, n = 10), or at an angle of 20°, representing vertebrae adjacent to a wedge fracture (20° groups, n = 10). Vertebral failure load and stiffness were the most important outcome measures. Results. The failure load was significantly higher (P = 0.028) when tested at 0° (2854 N, SD = 622 N), compared with vertebrae tested at 20° (2162 N, SD = 670 N). Vertebrae were also significantly stiffer (P < 0.001) when tested at 0° (4017 N/mm, SD = 970 N/mm) than those tested at 20° (2478 N/mm, SD = 453 N/mm). Conclusion. The failure load of osteopenic/osteoporotic vertebrae was 24% lower under off-axis loads (20°) than under axial loads (0°). This study may lead to a better understanding of the etiology of adjacent vertebral fractures after wedge-like deformities and demonstrates the importance of height reconstruction of wedge fractures in order to normalize the loading conditions on adjacent vertebrae.

Prophylactic vertebroplasty can decrease the fracture risk of adjacent vertebrae: An in vitro cadaveric study

Adjacent level vertebral fractures are common in patients with osteoporotic wedge fractures, but can theoretically be prevented with prophylactic vertebroplasty. Previous tests on prophylactic vertebroplasties have been performed under axial loading, while in vivo changes in spinal alignment likely cause off-axis loads. In this study we determined whether prophylactic vertebroplasty can also reduce the fracture risk under off-axis loads. In a previous study, we tested vertebral bodies that were loaded axially or 20° off-axis representing vertebrae in an unfractured spine or vertebrae adjacent to a wedge fracture, respectively. In the current study, vertebral failure load and stiffness of our previously tested vertebral bodies were compared to those of a new group of vertebral bodies that were filled with bone cement and then loaded 20° off-axis. These vertebral bodies represented adjacent-level vertebrae with prophylactic bone cement filling. Prophylactic augmentation resulted in failure loads that were comparable to those of the 0° group, and 32% greater than the failure loads of the 20° group. The stiffness of the prophylacticly augmented vertebrae was 21% lower than that of the 0° group, but 27% higher than that of the 20° group. We conclude that prophylactic augmentation can decrease the fracture risk in a malaligned, osteoporotic vertebra. Whether this is enough to actually prevent additional vertebral fractures in vivo remains subject of further study.

Does bone cement in percutaneous vertebroplasty act as a stress riser

Study Design. An in vitro cadaveric study. Objective. To determine whether percutaneous vertebroplasty (PVP) with a clinically relevant amount of bone cement is capable of causing stress peaks in adjacent-level vertebrae. Summary of Background Data. It is often suggested that PVP of a primary spinal fracture causes stress peaks in adjacent vertebrae, thereby leading to additional fractures. The in vitro studies that demonstrated this relationship, however, use bigger volumes of bone cement used clinically. Methods. Ten fresh-frozen vertebrae were loaded until failure, while registering force and displacement as well as the pressure under the lower endplate. After failure, the vertebrae were augmented with clinically relevant amounts of bone cement and then again loaded until failure. The force, displacement, and pressure under the lower endplate were again registered. Results. Stress peaks were not related to the location of the injected bone cement. Both failure load and stiffness were significantly lower after augmentation. Conclusion. On the basis of our findings, we conclude that vertebral augmentation with clinically relevant amounts of bone cement does not lead to stress peaks under the endplate. It is therefore unlikely that PVP, in itself, causes detrimental stresses in the adjacent vertebrae, leading to new vertebral fractures. Level of Evidence: N/A

Flow diverter implantation in a rat model of sidewall aneurysm: a feasibility study

Background More challenging animal models are needed to elucidate the efficacy of flow diverter (FD) designs and the mechanisms behind observed complications. The purpose of this study is to demonstrate the feasibility of implanting a FD in a sidewall aneurysm rat model. Methods An end-to-side anastomosis was created in the abdominal aorta of 36 rats using a decellularized donor pouch. A FD was subsequently implanted. Results After up to 3u2005months of follow-up, we observed that rats displayed normal growth and behavior. Mortality within the groups was low (2 rats, 5.6%). All aneurysms thrombosed after FD implantation and showed progressive soft tissue replacement of the thrombus during follow-up. The abdominal aortas remained patent. Conclusions This model can be used to test the effects of FDs in future studies.

Porous titanium particles for acetabular reconstruction in total hip replacement show extensive bony armoring after 15 weeks

Background and purpose — The bone impaction grafting technique restores bone defects in total hip replacement. Porous titanium particles (TiPs) are deformable, like bone particles, and offer better primary stability. We addressed the following questions in this animal study: are impacted TiPs osteoconductive under loaded conditions; do released micro-particles accelerate wear; and are systemic titanium blood levels elevated after implantation of TiPs? Animals and methods — An AAOS type-III defect was created in the right acetabulum of 10 goats weighing 63 (SD 6) kg, and reconstructed with calcium phosphate-coated TiPs and a cemented polyethylene cup. A stem with a cobalt chrome head was cemented in the femur. The goats were killed after 15 weeks. Blood samples were taken pre- and postoperatively. Results — The TiP-graft layer measured 5.6 (SD 0.8) mm with a mean bone ingrowth distance of 2.8 (SD 0.8) mm. Cement penetrated 0.9 (0.3–1.9) mm into the TiPs. 1 reconstruction showed minimal cement penetration (0.3 mm) and failed at the cement-TiP interface. There were no signs of accelerated wear, metallic particle debris, or osteolysis. Median systemic titanium concentrations increased on a log-linear scale from 0.5 (0.3–1.1) parts per billion (ppb) to 0.9 (0.5–2.8) ppb (p = 0.01). Interpretation — Adequate cement pressurization is advocated for impaction grafting with TiPs. After implantation, calcium phosphate-coated TiPs were osteoconductive under loaded conditions and caused an increase in systemic titanium concentrations. However, absolute levels remained low. There were no signs of accelerated wear. A clinical pilot study should be performed to prove that application in humans is safe in the long term.

Intracranial Aneurysm Expansion Might Cause Neurological Deterioration After Flow Diverter Treatment

OBJECTIVEnPatients with large and giant intracranial aneurysms (IAs) can experience neurological deterioration within 6 months after successful flow diverter (FD) placement. The purpose of the present study was to assess whether the occurrence of neurological deterioration can be linked to IA expansion within 6 months after FD treatment.nnnMETHODSnFrom 2010 to 2016, 45 FD procedures were performed in 44 patients with a large or giant IA. From this group, we selected all patients (14 patients with 15 IAs) with neurological deterioration within 6 months after FD treatment. All these patients had undergone follow-up imaging studies within the same period. The patients were then divided into 2 groups, those with mass effect-related and those with ischemia-related symptoms. The volumes of all treated IAs were determined through manual segmentation of the available pre- and postoperative imaging studies to determine IA expansion after FD treatment. To rule out false-positive findings, we only considered an IA volume increase of >20% after FD treatment as a true IA volume increase.nnnRESULTSnDuring the follow-up period, 6 IAs increased in volume and 9 IAs did not. More patients presenting with mass effect-related symptoms showed IA expansion (6 of 10 IAs) compared with patients presenting with ischemia-related symptoms (0 of 5 IAs; Fishers exact test, 2-sided; Pxa0= 0.044).nnnCONCLUSIONnThe volume of large and giant IAs can increase in the first 6 months after FD treatment. More patients presenting with mass effect-related symptoms showed IA expansion than patients with ischemia-related symptoms.

The Importance of Wall Apposition in Flow Diverters

BACKGROUNDnIt is assumed that high pore densities in flow diverters (FDs) are beneficial for intracranial aneurysm (IA) healing. However, various animal studies are not conclusive on the issue, suggesting that other factors are in play. One important factor might be wall apposition.nnnOBJECTIVEnTo (1) determine the relationship between FD pore density and aneurysm occlusion, and (2) determine the relationship between FD wall apposition and aneurysm occlusion.nnnMETHODSnSaccular aneurysms were microsurgically created in the aorta of 36 Wistar rats. Twelve rats received a low pore density FD (10 pores/mm2), 12 rats received a high pore density FD (23 pores/mm2), and the remaining 12 rats served as a control group. Six animals from each group were sacrificed 1 and 3 mo after surgery. We determined aneurysm occlusion, the number of struts not in contact with the aorta wall, and the average distance from malapposed struts to aorta wall through histology.nnnRESULTSnNo significant differences were found in aneurysm occlusion between the low pore density and high pore density groups (Pxa0>xa0.05) after 1 and 3 mo of follow-up. The average number of malapposed struts was lower for the occluded aneurysm group (4.4xa0±xa01.9) compared to the nonoccluded aneurysm group (7.7xa0±xa02.6, Pxa0<xa0.01). The average distance between malapposed struts and parent artery wall was lower for the occluded aneurysm group (33.9 μmxa0±xa011.5 μm) than for the nonoccluded aneurysm group (48.7 μmxa0±xa018.8 μm, Pxa0<xa0.05).nnnCONCLUSIONnWall apposition is more important than pore density for aneurysm occlusion.

Subtraction CTA: An Alternative Imaging Option for the Follow-Up of Flow-Diverter-Treated Aneurysms?

BACKGROUND AND PURPOSE: This was a pilot study to explore the diagnostic accuracy and safety of subtraction CTA combined with a single-energy metal artifact reduction algorithm (SEMAR) compared to DSA for the evaluation of intracranial aneurysm occlusion after flow diverter treatment. MATERIALS AND METHODS: We included patients treated with a flow diverter for an unruptured intracranial aneurysm between November 2015 and November 2016. The patient cohort comprised 2 groups: those who underwent follow-up imaging 1 month after flow-diverter treatment and those with a known residual intracranial aneurysm after flow diverter treatment who underwent imaging at regular follow-ups. Full-brain subtraction CTA was performed on a 320–detector row CT system. A low-dose non-enhanced volume acquisition was followed by a contrast-enhanced volume CTA. Iterative and noise-reduction filters, SEMAR, and SURESubtraction algorithms were applied. DSA was performed on a flat panel C-arm angiography system. Standard posteroanterior, lateral, 3D, and detailed 2D acquisitions were performed. Imaging was independently scored by 2 clinicians. Aneurysm occlusion (Raymond scale) was our primary outcome parameter. RESULTS: Thirteen intracranial aneurysms were evaluated with subtraction CTA and DSA. Nine aneurysm remnants were demonstrated by both subtraction CTA and DSA. The sensitivity and specificity of subtraction CTA for the detection of aneurysm occlusion were 100% (95% CI, 82.41%–100%) and 100% (95% CI, 67.55%–100%), respectively. Agreement between readers was perfect (κ = 1.0). The smallest neck remnant detected on subtraction CTA was 1.2 mm. No complications occurred. CONCLUSIONS: Subtraction CTA with single-electron metal artifact reduction is effective in the reduction of metal artifacts of flow diverters and might therefore be a viable alternative in the assessment of intracranial aneurysm occlusion after flow diverter treatment.

Presence of inflammatory proteins S100A8 and S100A9 in a giant intracranial aneurysm after flow diverter treatment

Abstract We demonstrate the presence of S100A8 and S100A9 proteins in the wall and thrombosed lumen of an enlarged intracranial aneurysm after flow diverter treatment. These proteins have shown to play an important role in vascular inflammation and may serve as a biomarker and potential therapeutic target for intracranial aneurysms.