Introduction: The aim of this study was to investigate if steroids enhance the vasoconstrictive effect of endothe-lin-1 (ET-1) on femoral arteries.

Materials and Methods: Ten female Wistar rats 59 to 88 days of age and 238 to 310 g of body weight, were used. Forty femoral artery segments were harvested. These arterial segments were mounted as ring preparations on a small vessel myograph. Two vessels from each animal were randomized to incubation with methylprednisolone 5 μg/ml [1] while the other 2 vessels were incubated with placebo. The arteries were stimulated cumulatively with endothelin-1. Isometric wall tension was quantified by the EC50; the vasoconstrictor concentration resulting in half maximal contraction.

Results: Thirty-eight arteries could be harvested in total; 20 were randomized to steroid treatment while 18 served as controls. The endothelin-1 dose-response curve displayed a stronger contraction for the steroid group in relation to the controls with increasing doses of ET-1. The EC50 of 4.4*10⁻⁸ M ± 1.8*10⁻⁸ M for the steroid vessels was lower compared to 5.9*10⁻⁸ M ± 3.4*10⁻⁸ M for the controls (mean ±SD; n.s.).

Discussion: Endothelin-1 is a potent vasoconstrictor. This study showed that incubation with methylprednisolone enhanced ET-1 mediated contraction of femoral arteries which can diminish blood flow within the vascular bed supplying the femoral head. This may be a relevant cofactor in the early pathogenesis of steroid-associated femoral head necrosis.

Introduction: The aim of this study was to investigate if steroids enhance the vasoconstrictive effect of nor-adrenaline on femoral arteries, which may result in femoral head blood flow reduction.

Materials and Methods: Ten male Wistar rats 62 to 88 days of age, 254 to 318 g of body weight, were used. Twenty femoral artery segments were harvested. These arterial segments were mounted as ring preparations on a small vessel myograph for isometric force measurements. The arteries were stimulated cumulatively with noradrenaline before and after incubation with methylprednisolone (5 μg/ml). Isometric wall tension was plotted and quantified by the EC50, the vasoconstrictor concentration resulting in halfmaximal contraction.

Results: The noradrenaline dose-response curve displayed a shift to the left for the steroid group in relation to the controls. This was reflected by a significantly lower EC50 of 9.5*10⁻⁷ M ± 5.1*10⁻⁷ M for the steroid vessels compared to 2.5*10⁻⁶ M ± 1.1*10⁻⁶ M for the control vessels (mean ± SD; p< 0.005).

Discussion: This study showed that incubation with methylprednisolone enhanced noradrenaline-mediated contraction of femoral arteries. Enhanced contraction of femoral arteries can diminish blood flow within the vascular bed supplying the femoral head. This may be a relevant cofactor in the early pathogenesis of steroid-associated femoral head necrosis.

Aims: We compared the primary rotatory stability of robot implanted hip endoprostheses with manually implanted stems. We examined three different types of prosthesisstems: Osteolock, CBC, Excia. Methods: 10 stems of each prosthesis type were implanted in identical polyurethan foam blocks: 5 manually, 5 robot assisted (CASPAR-System). The forces, which were necessary for the implantation of the stem were documented digitally. Now a deþnated rotatory stress was put on the stem with a torquing machine. The torsional moment was also documented digitally. Results: The strengthway- diagram of the implantation in robot assisted reamed foam blocks was homogeneous at each type of prosthesis. At the manually reamed blocks, the diagrams were very inhomogeneous.

The rotatory test showed also very unitary results at the robot implanted stems with only minimal variations of the results from the median. The range of results after manually implantation was much higher. In all types of protheses the use of the robot system lead to a signiþcantly higher rotatory stability. CBC stem is signiþcantly most stable for rotatory forces after robot assisted implantation compared to the other two types. After manual implantation there was no differrent stability between the CBC and the Osteolock stem. The Excia stem showed the signiþcantly lowers rotatory stability after manual and robot assisted implantation. Conclusions: With a robot system the primary rotatory stabilty of hip endoprosthesis is improved indenpendtly of the type of the prosthesis. The inßuence of the stem design is also important for the rotatory stability, too.