Locked versus standard unlocked plating of the pubic symphysis: a cadaver biomechanical study.
ABSTRACT Although locked plating has been shown to have advantages for diaphyseal and metaphyseal fracture fixation, its benefits for pubic symphyseal disruption have not been established. With traditional plate fixation of the disrupted pubic symphysis, normal physiological symphyseal pelvic motion eventually results in plate breakage, screw breakage, and loosening of screws. A concern exists that common modes of locked plate construct failure could result in abrupt and complete loss of symphyseal fixation. The purposes of this study were to determine, using an open-book pelvic injury model, whether locked plating of the pubic symphysis 1) offers any advantage over standard unlocked plating; and 2) results in a potential increased risk of abrupt fixation failure.
Twelve osteopenic cadaver pelvic specimens were acquired and dual-energy x-ray absorptiometry scans were obtained to ensure uniformity of the specimens' bone density. Sacrospinous, sacrotuberous, and anterior sacroiliac ligaments were released and the symphysis pubis was transected to simulate a partially stable open book (AO/Orthopaedic Trauma Association 61-B3.1) injury. Using a six-hole 3.5-mm plate specifically designed for the symphysis pubis with the capability of fixation in locked or unlocked mode, six pelvises were fixed with locked screws and six pelvises were fixed standard unlocked bicortical screws. There was no significant difference between these 2 groups with regard to bone density (P = 0.47). Two equally osteopenic pelvic specimens from each fixation group were selected for the purpose of obtaining failure data and determining an acceptable load for trialing. Both specimens failed at 1985 N. The remaining 10 pelvises were then mounted on a materials testing apparatus using the bilateral stance model as described by Tile. In accordance with the failure data, each pelvis was stressed at 440 N for a total of one million cycles (equivalent to 6.5 months of daily walking) or until fixation failure.
All pelvic specimens in both fixation groups completed one million cycles without plate or screw failure. However, diastasis of the initial pubic symphysis reduction was found in all pelvises (mean, 2.45 mm; range, 1.5-4.0 mm) regardless of fixation method. This loss of reduction was not significantly different between the 2 fixation groups (P = 0.914).
No abrupt failures occurred in either plating group. Consequently, any fear of catastrophic (ie, abrupt and complete) failure of locked symphyseal plates appears to be unfounded for open-book injuries treated in patients with low bone density. However, minor loss of the symphyseal reduction was evident in all pelvises regardless of the fixation method. Therefore, locked plating of the pubic symphysis does not appear to offer any advantage over the standard unlocked technique for an AO/Orthopaedic Trauma Association 61-B3.1 partially stable open-book pelvic injury pattern in osteopenic bone.
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ABSTRACT: The benefits of locked plating for pubic symphyseal disruption have not been established. The purpose of this biomechanical study was to determine whether locked plating offers any advantage over conventional unlocked plating of the pubic symphysis in the vertically unstable, Type-C pelvic injury. In each of eight embalmed cadaver pelvis specimens, sectioning of the pubic symphysis in conjunction with a unilateral release of the sacroiliac, sacrospinous, and sacrotuberous ligaments and pelvic floor was performed to simulate a vertically unstable Type-C (Orthopaedic Trauma Association 61-C1.2) pelvic injury. The disrupted SI joint was then reduced and fixed using two 6.5mm cannulated screws inserted into the S1 body. Using a six-hole 3.5mm plate specifically designed for the symphysis pubis having both locked and unlocked capability, four pelvises were fixed with locked screws and four pelvises were fixed with standard unlocked bicortical screws. Both groups were similar based on a dual-emission X-ray absorptiometry evaluation (P=0.69). Each pelvis was then mounted on a servohydraulic materials-testing apparatus using a bilateral stance model to mainly stress the symphyseal fixation and was cycled up to 1 million cycles or failure, whichever occurred first. Five specimens experienced failure at the jig mounting/S1 vertebral body interface, occurring between 360,000 and 715,000 cycles. Frank failure of the anterior or posterior instrumentation did not occur. However, end-trialing diastasis of the initial pubic symphysis reduction was found in all pelvises. There were no differences between the groups with respect to this loss of symphyseal reduction (P=0.69) or average cycles to failure (P=1.0). Pubic symphyseal locked plating does not appear to offer any advantage over standard unlocked plating for a Type-C (OTA 61-C1.2) pelvic ring injury.Injury 11/2013; DOI:10.1016/j.injury.2013.11.017 · 2.46 Impact Factor
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ABSTRACT: Background Implant loosening is frequently detected after fixation of Open Book injuries. Though many authors do not see this as a complication, it is often the reason for hardware removal or reinstrumentation in the case of remaining instability. We hypothesized that the flexibility of the implant has an influence on loosening and thus failure of the construct. Methods We used 6 fresh-frozen pelvic specimens and tested them with our recently introduced test setup for two-leg alternate loading. We subjected them to a non-destructive quasi-static test in the intact condition followed by a non-destructive cyclic test under axial sinusoidal loading with progressive amplitude. Afterwards we simulated an open book injury and performed fixation with three different configurations of a modular fixation system (1-, 2- or 4-rod configuration) in randomized order. Subsequently, specimens were subjected to 3 cyclic tests with the same loading protocol as previously defined. Finally, each construct was cyclically tested to failure keeping the final rod configuration. Findings We detected significantly greater mobility after 1-rod-fixation and no significant differences after 2-rod or 4-rod-fixation compared to the intact symphysis condition. In the destructive test series the 4-rod-fixation failed first followed by the 1-rod-fixation. The 2-rod-fixation sustained almost 3 times as many load cycles prior to failure as the 4-rod-fixation, while 1-rod-fixation sustained twice as many cycles as 4-rod-fixation. Interpretation In conclusion, flexible fixation of the ruptured pubic symphysis in human specimens shows superior behaviour with respect to load bearing capacity and ability to withstand cyclic loading compared to stiff constructs.Clinical Biomechanics 06/2014; DOI:10.1016/j.clinbiomech.2014.04.010 · 1.88 Impact Factor
European Journal of Trauma and Emergency Surgery 10/2014; 40(5):601-606. DOI:10.1007/s00068-013-0362-7 · 0.38 Impact Factor