Biomechanical approach to "open-book" pelvic ring injuries with flexible implants in comparison to rigid fixation

Status:

completed 12/2011

Aims:

The biomechanical stability of the pelvic ring is more than a relationship between the bony segments, it is the foundation of the entire musculoskeletal function. So far, various methods have been adopted to capture the movements of pubic symphysis with a focus on the non-injured anatomy. However, the existing biomechanical models, simulating either one-leg stance [Kraus, 1998] or symmetrical loading on both legs [Kim, 1999; Pohlemann, 1992; Varga, 1995], differ from the alternating physiological load during the gait. The aim of this study was to develop a new biomechanical testing model with two-leg alternate pelvic loading in order to measure movements at the pubic symphysis closer to reality.

Activities/Methods:

Six human cadaver pelvises with proximal femora and intact ligaments were mounted on a testing frame. The distal ends of the femora were constrained, allowing to move in the direction of the force, applied through the torsional actuator, and to rotate around the sagittal axis. The pelvis was allowed to rotate around the sacrum axis. Non-destructive cyclic sinusoidal loading with an increasing amplitude from 170 N to 340 N was applied over 1000 cycles. The movements at the pubic symphysis in all six degrees of freedom were evaluated in terms of translations and rotations in a co-ordinate system, adopted from Walheim, 1984a, using motion tracking.

Results:

The values of the translations and rotations at the symphysis were comparable to the data, collected from living subjects and reported in [Walheim, 1984a, 1984b] (Table 1). In addition, the study showcases a new biomechanical testing model with two-leg alternate pelvis loading allowing measurement of movements in pelvic ring joints in all six degrees of freedom, not biomechanically feasible with previous methods. A biomechanical testing model, simulating physiologic loads in the pelvic ring, is developed.

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