[Comparison of internal fixation methods for the symphysis in multi-directional dynamic gait simulation]

For the stabilization of the ruptured pubic symphysis, rigid forms of fixation such as plate osteosynthesis and flexible fixations such as wire loops or PDS banding have been recommended. All methods have only been tested by static unidirectional loading until failure of the system. By this experimental arrangement Ecke and Hofmann found comparable results for flexible and rigid methods of internal stabilization of the pubic symphysis. They preferred flexible methods to maintain mobility of the symphysis and to prevent symphyseal fusion. We tested dynamic compression plate osteosynthesis, reconstruction plate osteosynthesis, wire loops and PDS banding for internal fixation of injured pubic symphysis in a dynamic multidirectional experimental arrangement simulating gait conditions. The specimens were loaded with 85 N in vertical (y-) direction and 34 N in sagittal (z-) direction, which represent 50% of the forces acting at the pubic symphysis during walking and with a frequency of 1.5 Hz over 55,500 loads simulating the conditions over a 6-week mobilization period. Loading with 100% of the acting forces (corresponding to full weight bearing mobilization) led to early failure of the system. Our experimental analysis showed that neither wire loops nor PDS banding is able to stabilize the ruptured pubic symphysis, even immediately after fixation before loading. During the tests instability increased until failure of the system due to cutting of the bone or breaking of the wires or PDS banding. Success of plate osteosynthesis was dependent on the initial stability of the fixation. Overwinding of the screws, as in osteoporotic bone, lead to increasing loosening during repeated loading, whereas primary stable fixation of the screws was almost completely maintained during the test. In consequence, neither wire loops nor PDS banding should be used for stabilization of injured pubic symphysis if early mobilization with partial weight bearing is desired. Plate osteosynthesis (DC or reconstruction plate) tolerates early half weight bearing in patients with "open-book" injury only if safe screw fixation is guaranteed.