| Pelvic fractures are clinically complex injuries, accounting for 3.64% of fractures in adults, and occur as a result of high-energy trauma, such as falls and motor vehicle accidents. 68.3% of pelvic fractures are unstable fractures, which are serious injuries, and the mortality rate is up to 19%. Selecting appropriate treatment for unstable pelvic fractures remains a challenging problem for orthopaedic physicians. The stability of the pelvis is mainly related to the integrity of posterior pelvic ring. Therefore, the treatment of unstable pelvic fractures need to restore the continuity and stability of posterior pelvic ring as far as possible.Treatments of unstable pelvic fractures include conservative treatment and operative treatment. Conservative treatment has a significant chance of long-term complications: nonunion and malunion, pain, and neurologic dysfunction, more recently, scholars advocate operative treatment. Although the external fixation has the advantages of small wound and easily operation, there are some disadvantages of less stiffness, infection and loose. Greater stability of posterior pelvic ring can be achieved by internal fixation. There are a variety of methods available, including iliosacral(IS) screws, sacral bars, tension band plate(TBP), triangular osteosynthesis and so on. However, they have limitations.To address these limitations, we introduced a novel minimally invasive adjustable plate(MIAP) according to the structure characteristics of posterior pelvic ring. The primary biomechanical experiment found that MIAP could provide the stability of the pelvic ring. In this study, the pelvic fracture model was designed in standing position. And this article was designed to compare the stability of posterior pelvic ring disruptions fixed with three types of internal fixation in the following parts. Part 1 Biomechanical comparison of the stability of the Tile C pelvic fractures fixed with three kinds of internal fixatorObjective: To compare the stability of the Tile C pelvic fractures fixed with two IS screws, TBP and MIAP.Methods: Six embalmed specimens of adult pelvis were used, removing soft tissue but retaining intact spines from the fourth lumbar vertebra to the proximal one third of both femurs, intact pubic symphysis, bilateral sacroiliac joints and ligaments, bilateral hip joints, bilateral sacrotuberous ligaments and bilateral sacrospinous ligaments. The Tile C pelvic fractures were made. The symphysis pubis was fixed with plate, and the fracture of posterior pelvic ring was fixed with three kinds of internal fixator in random order. The specimens were placed in the biomechanical machine at a standing neutral posture. Vertical load of up to 500 N was applied and the displacement was recorded. The shift of fracture gap was measured by the grating ruler.Rusults: Under different vertical loads, the shift of fracture gap and displacement of the pelvic fractures fixed with two IS screws were similar to that fixed with MIAP, which was significantly smaller than that fixed with TBP.Conclusion: The stability of the Tile C pelvic fractures fixed with MIAP is similar to that fixed with two IS screws, and better than that fixed with TBP, under vertical load. Part 2 Establishment on three-dimensional finite element model of pelvisObjective: To build a normal pelvic finite element model. To analyze the strain, stress and the displacement distribution under vertical load.Methods: A normal adult male was chosen and scanned by computerized tomography(1-mm slice thickness). The results were conserved in DICOM format. The finite element model was made using the software of Mimics, Geomagic Studio, Solid Works, Abaqus. A loading of 500 N was put and the bilateral acetabulum was constrained. The strain, displacement and stress nephograms were obtained.Results: Under 500 N vertical load, the stress passed through sacrum, bilateral sacroiliac joint, the arcuate line to the bilateral acetabulum. The stress at pelvic anterior ring was very small. The strain concentrated of the model was small.Conclusion: The pelvis is a steady structure. Three dimensional finite element analysis provides a new method for the study of orthopeadic biomechanics, which will play more important role in the field of orthopeadic.Part 3 Three-dimensional finite element analysis of the stability of the unstable pelvic fractures fixed with three kinds of internal fixatorObjective: To compare the stability of unstable pelvic fractures fixed with three kinds of internal fixator by three-dimensional finite element analysis.Methods: To build the finite element model of unstable pelvic fracture. The fracture of posterior pelvic ring was fixed with three kinds of internal fixator. A loading of 500 N was put and the bilateral acetabulum was constrained. The strain, displacement and stress nephograms of the pelvic model and the shift of fracture gap were obtained.Results: Under 500 N vertical load, the strain concentrated of the model was very small. The displacements of pelvic model were IS model(1.863mm); MIAP model(6.887mm); TBP model(9.103mm). The shift of fracture gap in pelvic model was IS model(1.749mm); MIAP model(2.999mm); TBP model(9.103mm).Conclusion: Under vertical load, the stability of the unstable pelvic fractures fixed with MIAP is less than that fixed with two IS screws, and better than that fixed with TBP. Part 4 Comparison on efficacy of two internal fixations for unstable pelvic fracturesObjective: To compare the efficacy of the minimally invasive adjustable plate(MIAP) and two iliosacral(IS) screws in treatment of unstable pelvic fractures.Methods: This study involved 43 patients with unstable pelvic fractures from May 2009 to November 2012.Of these, 21 patients had injury caused by traffic accident, 16 by fall from height, and 6 by crush. Twenty-two patients were treated with MIAP(Group A) and 21 were treated with two IS screws(Group B). Preoperative mean injury severity score(ISS) was 14.5 points in Group A and 11.7 points in Group B. According to AO classification, Group A had 9 patients with type B and 13 patients with type C injuries, and Group B had 11 patients with type B and 10 patients with type C injuries. This two internal fixations were compared in aspects of intraoperative blood loss, operation duration, length of incision, number of X-ray exposures and Majeed postoperative functional evaluation.Results: All 43 patients were followed up for 13-48 months(mean duration 25.6 months). Operation duration, length of incision, and intraoperative blood loss in Group A were longer than that in Group B, however, the number of X-ray exposures in Group A was significantly less than that in Group B. There was no statistical difference for postoperative Majeed function score between the two groups. Fracture malunion occurred in two patients in Group B postoperatively.Conclusion: Both MIAP and two IS screws can provide sufficient fixation for unstable pelvic fractures. The MIAP is easy to perform with technically safe, good reduction and less radiation exposure. |
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