Biomechanical comparison of two stabilization techniques for unstable sacral fractures.

AIM: The purpose of the study was to assess the stability provided by an ilio-iliac dorsal plate fixation technique using an AO narrow DCP on the pelvic brim in vertically and rotationally unstable type-C pelvic ring injuries. MATERIALS AND METHODS: We examined 12 fresh cadaver pelvises in a single limb stance load. A type-C pelvic ring injury (a type I lateral sacral fracture in the classification of Denis with symphysis pubis rupture) was performed on the cadaver specimen and fixed with a four-hole narrow dynamic compression plate to stabilize the symphysis pubis rupture; the sacrum fracture was stabilized either anteriorly with two 3-hole reconstruction plates ("anterior plate osteosynthesis") or with a posterior fixation using a 12-hole narrow DCP. A cyclic load of between 100 and 250 N was applied to the fifth lumbar vertebra of the specimen. An extensometer was attached to both sides of the sacrum fracture to detect movements at the fracture site. RESULTS: We were able to achieve usable measurements in nine specimens. Three measurements were performed on each specimen, and the movements recorded at the fracture gap in trans-sacral plate fixation were higher than or similar to those observed for anterior plate synthesis in 23 out of 27 cases. CONCLUSION: Dorsal ilio-iliac bridge plate fixation provides somewhat reduced stability compared to anterior plate fixation, but the difference is not significant.

Critical analysis of in vitro stability testing of spinal implants and proposal for standardization.

BACKGROUND: The American Society for Testing and Materials (ASTM), considered the gold standard worldwide, requires only testing in physiological saline solution to simulate in vivo conditions in standard testing of spinal implants. RESEARCH DESIGN AND METHODS: We conducted an in vitro study to identify an industrial lubricant with characteristics that are most similar to those of biologically lubricating fat, blood, and tissue fluids. The use of such a material could standardize the results of in vitro mechanical tests for better clinical applications. RESULTS: Our study has shown that the lubricity of physiological saline was well below that of human soft tissues and tissue fluids, and among the motor oils, Castrol GTX3 provided a testing environment similar to that of a living organism. CONCLUSIONS: With the intention of standardizing and preventing a biological hazard, we have developed a reproducible mechanical testing proposal based on our experiments, which, in addition, would allow us to avoid many misunderstandings and contingencies.

Further development of our finite element pelvic model to compare fixation methods for pelvic fractures.

OBJECTIVES: In this study, we aimed to create a realistic model which is suitable for computerized simulation of any kind of fractures and provides reliable results. PATIENTS AND METHODS: We used a plastic pelvic model to construct advanced specimens. The data were retrieved from the computed tomography scans of a healthy pelvis. A geometrically exact model by the means of three-dimensional scanning of the plastic pelvis was obtained. The material properties of the bony parts based on the data retrieved from the computed tomography scans were modified. The pelvis was divided into distinct segments and the proportion of the cortical and cancellous bone substance in each segment were determined to make the material properties accurate. In the validation of the pelvic model, a type C pelvic injury was simulated and the fracture of the sacrum and the symphyseolysis were stabilized with plates. These data were compared with those of previously performed cadaver experiments. RESULTS: Based on the simulation performed on the new model, the shift values between the fragments of the broken sacrum approximated the reported values of our cadaver experiments and also arising strains remained in the tolerable interval. CONCLUSION: Our new finite element pelvic model represents the pelvis more accurately than the former one. As the validation of the model was successful, it is suitable for computerized simulation of any kind of fractures offering reliable results.

Does surgically fixation of pubic fracture increase the stability of the operated posterior pelvis?

OBJECTIVES: This study aims to investigate whether surgical treatment of pubic rami fractures increases the stability of the posterior pelvis. PATIENTS AND METHODS: A finite element pelvic model with improved geometric and material characteristics was analyzed. By imitating a standing position, a type I Denis sacrum fracture and a unilateral pubis fracture, we measured the differences in tension and displacement. The posterior injury was treated with a direct plate synthesis or transsacral plate synthesis, while the pubis fracture was left without fixation or fixed with either a retrograde pubic screw or plate synthesis. RESULTS: The operative fixation of pubic rami fractures decreased the movement in the fracture gap not only at the site of the pubis fracture, but also at the site of the fixed sacrum fracture. The plate synthesis provided greater stability of the anterior fracture than the retrograde screw. The tensions in the implants were below the allowed values. CONCLUSION: We concluded that surgically fixation of pubic fracture increases the stability of the operated posterior pelvis.