Experimental analysis of Hoffmann external fixation in various mountings.

The mechanical properties of four different configurations of the Hoffmann external fixation system were tested in an experimental setup using 4-mm stainless steel pins. Furthermore, stainless-steel pins and titanium pins 5 mm in diameter were applied in one of the fixators. The evaluation of the results was based on a paired t-test, with P less than 0.05 as the significance level. The quadrilateral transfixing Hoffmann-Vidal frame (HVF) proved to be the most rigid fixator under all loading conditions. The unilateral frame type supplied with two connecting bars and four ball joints was significantly more rigid than the unilateral single-bar device. By increasing the pin diameter from 4 to 5 mm a further increase of stiffness could be achieved, thus reaching about two-thirds of the rigidity of the HVF. The difference between titanium and stainless steel pins was not significant. Common for all the frame mountings was a fivefold greater rigidity in the lateral direction (in the plane of the pins) than in the anteroposterior direction (perpendicular to the pins).