Comparison of different methods of internal fixation of symphyseal disruptions under multidirectional dynamic conditions: an experimental analysis simulating gait conditions

Abstract

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.

Novel minimally invasive tape suture osteosynthesis for instabilities of the pubic symphysis: a biomechanical study

“…The forces applied to the symphysis during this study were based on prior studies of Meissner et al and Walheim et al These authors studied the physiological mobility of the pubic symphysis and the concomitant impacting forces [8,13,31]. Accordingly, when applying physiological forces to the isolated symphysis with the biomechanically significant posterior pelvic ring previously excluded, the symphysis is not able to bear the entire load and will inevitably rupture, independently from any applied osteosynthesis [13]. Consequently, the authors suggested a maximum of + 75 N and a minimum of −75 N during cyclic loading which was adopted in this study in order to ensure a reasonable biomechanical comparison of the tested osteosynthesis methods [13].…”

“…The pelvises were mounted into an all-electric industrial loading machine (Instron ElectroPuls ™ E10000 Linear-Torsion, Norwood, MA, USA) (see Fig. 2) and an 8-step testing protocol based on Meissner et al [13] (see Table 1) was applied. In this study, Meissner et al initially tried to simulate full body weight on an isolated symphysis which, 1 3 however, led to the failure of all implants [13].…”

“…2) and an 8-step testing protocol based on Meissner et al [13] (see Table 1) was applied. In this study, Meissner et al initially tried to simulate full body weight on an isolated symphysis which, 1 3 however, led to the failure of all implants [13]. Ultimately, the original forces were then cut in half, leading to realistic biomechanical results [13] and finally preparing the ground for the forces used in this experimental study.…”

“…The statistical analysis was performed with IBM SPSS Statistics (Windows, version 26.0, IMB Corp., Armonk, NY, USA). Based on data presented by Meissner et al [13], we estimated that nine specimens would yield 94% power at the 5% significance level.…”

“…To address these issues, several approaches have been investigated using numerous internal fixation methods such as cerclages and self-degrading Polydioxanon (PDS)-bandings [13], internal fixators [14] and two-hole plates [11,15]. Yet, these methods also display a high rate of implant failure based on an insufficient fixation of the symphyseal joint prior to a ligament healing [13,16].…”