[Complex ligament instabilities after "open book"-fractures of the pelvic ring - finite element computer simulation and crack simulation]. / Komplexe ligamentäre Instabilitäten nach "open book"-Verletzungen des Beckenrings - Finite-Elemente-Computersimulation und Bruchversuch.

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.

The sacrotuberous and the sacrospinous ligament--a virtual reconstruction.

Little is known about the morphometric properties of the sacrotuberous ligament (ST) and the sacrospinous ligament (SS). The influence of ligaments on pelvic stability and the extent of reconstruction in case of instability are controversially discussed. The ST and the SS of 55 human subjects fixed in alcohol solution and of four fresh cadavers were measured. Both ligaments were defined as geometric figures. The ST was a contorted bifrustum, while the SS was a contorted frustum, both with elliptic planes. In all cases investigated, the ST and the SS fibres were twisted. For men, the ST and the SS had a mean length of 64 and 38 mm. For women, lengths of 70 and 46 mm were measured in the ST and the SS. The ST length, height and cross-sectional area showed gender-specific differences at statistically significant level. The ST and the SS volumes correlated closely, regardless of gender or side. Measurements of fresh ligaments of four unfixed cadavers showed similar results. The data obtained were then used to generate computer-based three-dimensional models of both ligaments, using the Catia software. Conclusively, the virtually generated ST and SS are suitable models to be included in pelvic fracture simulation, using the finite element method.