Aims. to investigate the stiffness and strength of completely unstable pelvic fractures þxated both anteriorly and posteriorly under cyclic loading conditions. Methods: In 12 specimens a Tile C1 pelvic fracture was created. We compared the intact situation to anterior plate þxation combined with one or two SI screws. In 2000 measurements each pelvis was loaded with a maximum of 400N. The translation and rotation stiffness of the þxations were calculated using a 3-dimensional video system. Furthermore the load to failure and the number of cycles before failure were determined. Results: Both translation and rotation stiffness of the intact pelvis were superior to the þxated pelvis. No difference in stiffness was found between the techniques with one or two sacroiliac screws. However a signiþcantly higher load to failure and signiþcantly more loading cycles before failure could be achieved using two sacroiliac screws compared to one screw. Conclusions: Although the combination of anterior plate þxation combined with two sacroiliac screws is not as stable as the intact pelvis, in this study embalmed aged pelves could be loaded repeatedly with physiological forces. Given the fact that the average trauma patient is younger and given the fact that the quality (or grip) of the þxation was a signiþcant covariable for longer endurance of the þxation, this suggests that further clinical research into direct postoperative weight bearing can be undertaken safely.

Aims. to investigate whether the stability of partially unstable pelvic fractures can be improved by combining plate þxation of the symphysis with a posterior sacroiliac screw. Methods: In 6 specimens a Tile B1 (open book) pelvic fracture was created. We compared the intact situation to isolated anterior plate þxation and plate with SI screw þxation. Using a 3-dimensional video system we measured the translation and rotation stiffness of the þxations and the load to failure. Results: Neither absolute displacements at the os pubis or at the sacroiliac joint or stiffness of the ilium in respect to the sacrum were signiþcantly different for the techniques with or without sacroiliac screw or the intact situation. Load to failure was only reached in one of the six cases. In all other cases the þxation of the pelvis to the frame failed before failure of the þxation itself. In these cases a load of about 1000N or more could be applied. Conclusions: The addition of a sacroiliac screw in a Tile B1 fracture does not give signiþcant additional stability. Although cyclic loading was not tested, in these experiments forces could be applied similar to full body weight. Clinical experiments into direct postoperative weight bearing are recommended to examine the clinical situation.