The accompanying shear force at the point of bone opposition is an important factor inherent to tibial fracture stability during axial loading. We determined at which angle of fracture obliquity shearing becomes a dominant force after stabilization with circular external fixation, and how modifications to the external fixator can reduce this effect. We constructed tibial fracture models with a successively increasing fracture angle obliquely (from 0°to 60°) to determine the stability in the classic Ilizarov frame and subsequent frame modifications during axial loading (maximum, 1000 N). Stability was determined by measuring the fracture line displacement for each fracture obliquity model after an applied axial load. Fracture line displacement was recorded as coordinate component changes as measured by an ultrasonic digitizer. We defined construct stability as less than 2 mm of fracture line migration with loading. More than 3500 data points were collected for this study. The classic Ilizarov construct successfully stabilized fractures with up to 30°of fracture obliquity, after which divergent instability occurs. The addition of proximal and distal perpendicular half-pins provides little benefit. Arced wires provided stability up to 40°fracture obliquity. A formal steerage pin construct provided stability for all fracture models (up to 60°of fracture obliquity) with all applied loads (up to 1000-N axial load).
Purpose: To examine experimentally the feasibility of transfemoral endoluminal repair of aneurysms containing the ostia of essential branch arteries. Methods: In a canine model (n = 4), suprarenal aortic aneurysms were created by suturing an artificial patch onto an anterior arteriotomy. Following a 2-week recovery period, the dogs underwent endovascular exclusion of their aneurysms using an aortic stent-graft with separate renal artery branch grafts. Outcome was evaluated using angiography, intravascular ultrasound (IVUS), Doppler flow, invasive pressure monitoring, and autopsy, respectively. Results: Successful creation and subsequent endovascular exclusion of the aneurysm using aortic stent-grafts and separate bilateral renal artery stent-grafts was achieved in all trials. Angiographically, all aneurysms were excluded from aortic flow and all renal arteries were patent at completion of the procedure. With IVUS, good graft apposition and absence of perigraft flow were demonstrated in all animals. Mean pressure in the aneurysmal sac at completion of the procedure was 40 ± 7 mmHg, compared to a mean systemic blood pressure of 105 ± 8 mmHg (p < 0.05). At autopsy, no gross intimal damage was seen in the aorta or the renal arteries, and intact aortic grafts and branch grafts without twisting, coiling, or kinking were found in all trials. Conclusions: In an acute animal model, suprarenal aortic aneurysms can be excluded from the circulation with preservation of renal flow using an endoluminally placed aortic stent-graft with separate branch grafts.
In an acute animal model, suprarenal aortic aneurysms can be excluded from the circulation with preservation of renal flow using an endoluminally placed aortic stent-graft with separate branch grafts.
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