In vitro testing of a novel implant for angular stabilisation of the posterior pelvic ring

Dorsal pelvic ring fractures occur in younger patients due to high-energy trauma or in elderly patients due to osteoporosis as fragility fractures of the pelvis (FFP). To date, there is no consensus on the optimal stabilization technique to treat fragility fractures of the posterior pelvic ring. The purpose of this biomechanical in vitro study was to evaluate a novel angle-stable nail system with respect to its stabilising ability in comparison with established procedures.

Eight fresh frozen human pelvic specimens (51-90 years, BMD 40-111 mg CaHA/cm³), were destabilised using a standardised FFP IIb fracture model according to Rommens and Hofmann (equivalent to AO/OTA 61C1.3) and consecutively stabilised with the different implant systems. The intact, fractured, and surgically treated pelvises were tested in a custom-developed pelvic test set up integrated into a universal spine tester. For simulating daily-life loading scenarios, physiological loads were applied to the specimen via the femora and four muscle pulls. The test protocol consisted of a two-legged stance in two loading conditions, respectively, which was followed by an alternating, gait-like stance testing protocol. Instability was assessed via the relative displacements at the fracture gaps.

The relative displacements of the fractured pelvic specimens showed significant destabilization of the pelvis compared to the intact state (p < 0.05) which could be reversed with the novel implant as well as with all conventional treatment techniques to a certain extent.

Surgical instrumentation of dorsal pelvic ring fractures appear to be primary stable enough to allow immediate weight bearing. From a biomechanical point of view, the novel nail implant seems to be comparable or even slightly superior to already established procedures for stabilization of pelvic insufficiency fractures. However, the current clinical standard of treating FFP type IIb fractures with S1 screws has been biomechanically confirmed. Lumbopelvic suspension and S2 screws should not primarily be used for stabilization of dorsal pelvic fractures of type IIb or higher but may alternatively be used in patients in whom implantation of the novel implant or S1 screws is not possible due to anatomic conditions.