Purpose
Simple 2-dimensional (2D) analyses of bone strength can be done with dual energy x-ray absorptiometry (DXA) data and applied to large data sets. We compared 2D analyses to 3-dimensional (3D) finite element analyses (FEA) based on quantitative computed tomography (QCT) data.
Methods
213 women participating in the Study of Women’s Health across the Nation (SWAN) received hip DXA and QCT scans. DXA BMD and femoral neck diameter and axis length were used to estimate geometry for composite bending (BSI) and compressive strength (CSI) indices. These and comparable indices computed by Hip Structure Analysis (HSA) on the same DXA data were compared to indices using QCT geometry. Simple 2D engineering simulations of a fall impacting on the greater trochanter were generated using HSA and QCT femoral neck geometry; these estimates were benchmarked to a 3D FEA of fall impact.
Results
DXA-derived CSI and BSI computed from BMD and by HSA correlated well with each other (R= 0.92 and 0.70) and with QCT-derived indices (R= 0.83–0.85 and 0.65–0.72). The 2D strength estimate using HSA geometry correlated well with that from QCT (R=0.76) and with the 3D FEA estimate (R=0.56).
Conclusions
Femoral neck geometry computed by HSA from DXA data corresponds well enough to that from QCT for an analysis of load stress in the larger SWAN data set. Geometry derived from BMD data performed nearly as well. Proximal femur breaking strength estimated from 2D DXA data is not as well correlated with that derived by a 3D FEA using QCT data.
Introduction
Coiling procedures for intracranial aneurysms (IAs) performed in the US have steadily increaseda, and volumetric efficiency may become an important consideration for hospitals. Coil volume depends on length and primary wind diameter (PWD), and volumetric efficiency can be achieved by either inserting more coils or using coils with larger volumetric filling. This scenario analysis evaluates the influence of PWD and length on total coil volume by comparing four similar Stryker and CEREPAK coils.
Methods
In this analysis, we test the influence of PWD (D2) and length (L) on the Coil Volume Formula: [Π(D2/2)2(L)]c. In two hypothetical scenarios, relative percent difference in total coil volume was calculated and compared between four Stryker Target 360 coils and four similar CEREPAK coils that were matched based on closest PWD and L. In scenario I, L remained constant and D2 varied. In scenario II, D2 and L were inversely varied. In both scenarios, coil volume achieved by CEREPAK and Stryker coils was calculated and descriptively compared.
Results
Scenario I: (a) Stryker Target XL 360 10mm x 40cm (D2 = 0.014”, length = 40cm) with volume of 39.726mm3 was matched to the CEREPAK Heliform XL 10mm x 40cm (D2 = 0.015”, length = 40cm) with 15% greater volume of 45.604mm3. (b)Stryker Target 360 3mm x 6cm (D2 = 0.010”, length = 6cm) with volume 3.040mm3 was matched to the CEREPAK Freeform 3mm x 6cm (D2 = 0.012”, length = 6cm) with 44% greater volume of 4.378mm3. Scenario II: (a) Stryker Target XL 360 12mm x 45cm (D2 = 0.014”, length = 45cm) with volume 44.692mm3 was matched to the CEREPAK Heliform XL 12mm x 42cm (D2 = 0.015”, length = 42cm) with 7% greater volume of 47.884mm3. (b)Stryker Target 360 5mm x 20cm (D2 = 0.010”, length = 20cm) with volume 10.134mm3 was matched to the CEREPAK Freeform 5mm x 15cm (D2 = 0.012”, length = 15cm) with 8% greater volume of 10.945mm3.
Conclusions
The four selected CEREPAK coils compared to four equivalent Stryker coils achieved higher total coil volume in all scenarios. An increase in PWD by as little as 0.001”‐0.002”, improved relative coil volume by 15%‐44% (with equivalent coil length) and 7–8% (with varied coil length by 3–5cm). Clinicians evaluate many coil characteristics when treating an IA, however, PWD might be given consideration over length due to its impact on total coil volume.
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