Causes and effects of spinal fractures

Contains fulltext : 112258.pdf (publisher's version ) (Open Access)Radboud Universiteit Nijmegen, 2 juli 2013Promotor : Verdonschot, N.J.J. Co-promotores : Homminga, J.J., Tanck, E.J.M

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

Item does not contain fulltextSTUDY 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 degrees group, n = 10), or at an angle of 20 degrees , representing vertebrae adjacent to a wedge fracture (20 degrees groups, n = 10). Vertebral failure load and stiffness were the most important outcome measures. RESULTS: The failure load was significantly higher (P 5 0.028) when tested at 0 degrees (2854 N, SD 5 622 N), compared with vertebrae tested at 20 degrees (2162 N, SD 5 670 N). Vertebrae were also significantly stiffer (P, 0.001) when tested at 0 degrees (4017 N/mm, SD 5 970 N/mm) than those tested at 20 degrees (2478 N/mm, SD 5 453 N/mm). CONCLUSION: The failure load of osteopenic/osteoporotic vertebrae was 24% lower under off-axis loads (20 degrees ) than under axial loads (0 degrees ). 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

The contradictory effects of pores on fatigue cracking of bone cement.

Contains fulltext : 48199.pdf (publisher's version ) (Closed access)The beneficial effect of porosity reduction on the fatigue life of bone cement has been demonstrated in numerous experimental studies. Clinically, however, it seems that the beneficial effect of porosity reduction of cement around total hip replacement components can only be found in large follow-up studies. Little is known about the actual mechanical effect of a pore on fatigue crack formation in cement mantles. We studied the effect of pores on the crack formation process in a finite element model of a transverse slice of a total hip reconstruction. We created models with a single large pore and models with multiple pores at levels of 2, 4, and 9%. The models were cyclically torque-loaded, causing macrocracks to appear in the cement mantle. In all models, we found that pores acted as microcrack initiators. However, pores could have both a detrimental and a beneficial effect on the macrocrack propagation in the cement mantle. Both effects were seen in the models with a single large pore and in the models with multiple pores. Pores would either accelerate, deviate, or decelerate the macrocrack propagation in the cement mantle. The effect of the pores depended on the location of the pores with respect to the stress intensities in the model, but was independent of the pore size or the level of porosity. The results may explain why the beneficial effect of vacuum mixing is difficult to demonstrate clinically. Stress intensities that are present in a cement mantle in an in vivo situation may overshadow the detrimental effect of a pore, while the beneficial effect may become more pronounced

Finite-element analysis of failure of the Capital Hip designs.

Contains fulltext : 47857.pdf (publisher's version ) (Closed access)The Capital Hip implant was a Charnley-based system which included a flanged and a roundback stem, both of which were available in stainless steel and titanium. The system was withdrawn from the market because of its inferior performance. However, all four of the designs did not produce poor rates of survival. Using a simulated-based, finite-element analysis, we have analysed the Capital Hip system. Our aim was to investigate whether our simulation was able to detect differences which could account for the varying survival between the Capital Hip designs, thereby further validating the simulation. We created finite-element models of reconstructions with the flanged and roundback Capital Hips. A loading history was applied representing normal walking and stair-climbing, while we monitored the formation of fatigue cracks in the cement. Corresponding to the clinical findings, our simulation was able to detect the negative effects of the titanium material and the flanged design in the Capital Hip system. Although improvements could be made by including the effect of the roughness of the surface of the stem, our study increased the value of the model as a predictive tool for determining failure of an implant

Elevation of inflammatory S100A8/S100A9 complexes in intracranial aneurysms

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