[Complex ligament instabilities after "open book"-fractures of the pelvic ring - finite element computer simulation and crack simulation].

BACKGROUND: Instability of pelvic ring fractures is also caused by ligament disruption. Classifications are based on the major forces leading to fracture. Data from injury mechanisms as well as clinical and radiological criteria are used to determine the degree of instability. The major aim of all kinds of stabilisation is the anatomic reconstruction of the bony pelvic ring. The injured ligamentous apparatus is still ignored. Some clinical trials assume that soft-tissue injuries may be the reason for the poor patient outcome in "open book" pelvic ring fractures. The aim of the study was to develop a realistic finite element (FE) computer model to simulate "open book" fractures and predict injury-associated instabilities for osteosynthesis planning. PATIENTS/MATERIAL: We developed a realistic FE computer model of the pelvic ring based on CT data. With anatomic studies a computer model of the ligamentous apparatus was created and inserted into the pelvic ring to complete the bone-ligament complex. Numerical simulations were performed to identify the influence of single pelvic ligaments on the shifting at the intact anterior and posterior pelvic ring. Additionally, a biomechanical validated virtual crack simulation with anterior-posterior compression forces was undertaken to predict complex instabilities in "open book" pelvic ring fractures. RESULTS: The pelvic ligaments have local and general stabilising functions. The sacrospinous and sacrotuberous ligaments are providing the vertical load transfer, whereas the ligaments of the iliosacral joint and the iliolumbal ligament are necessary for the horizontal load transfer. In "open book" fractures ligaments are ruptured stepwise from anterior to posterior. If the intraosseous and posterior ligaments of the iliosacral joint are intact, only single rotational instability along the ipsilateral iliosacral joint occurs. If the ligaments at the posterior pelvic ring are ruptured too, a second axis across both iliosacral joints was measured. In this particular case additional stabilisation of the posterior pelvic ring should be performed. CONCLUSION: With numerical simulations, prediction of injury-associated instabilities is possible. Because of incomplete radiological data the implementation of patient-specific FE pelvic computer models into the clinical routine is still not realistic.