| BackgroundUnstable pelvic fractures resulted mostly from high-energy injury, often associated with serious blood vessels, nerves and other organ injury, and have higher mortality and morbidity. The aim of early treatment is to save lives and reduce mortality. The subsequent treatments are aimed at reconstruct the continuity and stability of the pelvic ring in order to reduce complications and restore the labor and life skills. With the development of modern medical technology and further understanding of anatomy, injury mechanism and biomechanics features of the pelvis, it has made great progress in the management of pelvic fracture. However, unstable pelvic fractures are still a challenging problem both in the immediate post injury phase and later when definitive fixation is undertaken.Posterior pelvic ring is the critical area of weight-bearing and transmitting loads, and it is also the major stabilizing structure of pelvic ring. Biomechanical study has shown that60%of pelvic stability comes from the posterior structures,40%from the anterior. And the reconstruction of posterior pelvic ring has been the focus of clinical and biomechanical research. The current methods of treatment include sacral bars, anterior sacroiliac plates, iliosacral screws, triangular osteosynthesis and tension band plate. However, these fixation techniques have the advantages and disadvantages respectively. And the optimal fixation methods remain unclear.It has achieved excellent clinical results using the tension band plate for unstable pelvic ring injury. The posterior tension band plate osteosynthesis presents a comparatively stable, minimally invasive method for the posterior pelvic ring reconstruction in unstable pelvic injury. However, there are few biomechanical analysis of the tension band plate for unstable pelvic fracture. This study is designed to provide biomechanical basis for further reasonable and effective application of tension band plate for posterior pelvic ring injury by systematic biomechanical study. Furthermore, we design a new modified tension band plate and evaluate the biomechanical stability of posterior pelvic ring fixed with the modified tension band plate in the current study.PART I Effects of fixation position on the stability of posterior pelvic ring fixed using tension band plate:a biomechanical studyObjectiveTo compare the effect of three different fixation positions on the stability of the posterior pelvic ring fixed with tension band plate in cadaver pelvis specimens in order to identify the optimal fixation position of tension band plate for posterior pelvic ring reconstructionMethods8adult cadaver pelvic specimens (male5, female3, aged from24to53) were used to simulate the AO type C1.2pelvic injury (pubic symphysis diastasis and unilateral sacroiliac joint disruption). Each intact pelvic specimen was firstly tested as a control group before the model of unstable pelvic injury was made. The posterior ring of each pelvis was constructed in randomized order with tension band plate in the following three different position:Fixation position1:the plate was fixed to bilateral posterior superior iliac spines, and the plate at both ends pointed to the pubic symphysis (roughly parallel with the pelvic boundaries, point downward and forward); Fixation position2:the plate was located at the posterior of iliac crest above the posterior superior iliac spine level, the plate at both ends pointed forward. Fixation position3:the plate was located at the posterior of iliac crest under the posterior superior iliac spine level, the plate at both ends pointed upward and forward. The anterior pelvic ring of each specimens of was fixed with3.5mm reconstruction plate. All pelvic specimens were mounted in the bio-mechanical testing machines in order that a0-600N vertical load and a0～8N·m torsional load were performed. The vertical displacement and torsional angle of the whole pelvic were measured and recorded by the displacement sensors of the bio-mechanical testing machine. The axial stiffness and torsional stiffness of the pelvis were calculated. Under0～600N vertical load, the relative displacement of the sacrum and ilium of the involved sacroiliac joint in the vertical, horizontal, and anteroposterior direction and the rotation of sacrum relative to the iliac in the sagittal plane were measured and recorded by the prepositioned posterior pelvic ring displacement sensors. Statistical analysis was performed using the analysis of variance test (ANOVA) with repeated-measures for multiple comparisons.ResultsUnder0～600N vertical load, the whole pelvic vertical displacement of the fixation position1was the smallest (2.470±0.201mm), compared with the fixation position2(2.896±0.271mm) and the fixation position3(2.714±0.232mm), the difference was statistically significant (P<0.05). The difference between the fixation position2and the fixation position3was also statistically significant (P<0.05). The whole pelvic axial stiffness of the fixation position1was73.3%of the intact pelvis,62.5%and66.7%in the fixation position2and the fixation position3respectively. The differences were statistically significant (P<0.05). Under0～8N·m torsional loads, the whole pelvic torsional angle of the fixation position1was the smallest (3.285±0.354°), compared with the fixation position2(3.644±0.388°) and the fixation position3(3.610±0.420°), the difference was statistically significant(P<0.05). The whole pelvic torsional stiffness of the fixation position1was72.7%of the intact pelvis, the fixation position366.2%, and the fixation position265.5%. Under0～600N vertical load, the displacement of the sacroiliac joint in the vertical, horizontal, and anteroposterior direction and the rotation displacement in the sagittal plane of the fixation position1, compared with fixation positions2and3, was smallest, and the difference was statistically significant (P<0.05). The displacement of fixation position1was minimum (vertical displacement:1.390±0.118mm, horizontal displacment:0.340±0.070mm, anteroposterior displacement:0.441±0.056mm, sagittal rotation:1.125±0.282°), followed by a fixation position3(vertical displacement:1.570±0.069mm, horizontal displacement:0.438±0.107mm, anteroposterior displacement:0.548±0.098mm, sagittal rotation:1.475±0.212°), and the fixation position2was the largest (vertical displacement:1.661±0.072mm, horizontal displacement:0.484±0.105mm, anteroposterior displacement:0.621±0.066mm, sagittal rotation1.613±0.285°). The difference between the fixation position3and the fixation position2was also statistically significant (P<0.05).ConclusionsUnder both vertical and torsional load, it is the optimal fixation position of tension band plate osteosynthesis for posterior pelvic ring injury that the tension band plate is fixed to bilateral posterior superior iliac spines and the plate at both ends point to the pubic symphysis. And the tension band plate which is fixed under the posterior superior iliac spine level (the plate at both ends point to the pubic symphysis) is better than the tension band plate fixed above the posterior superior iliac spine level(the plate at both ends pointed forward). PART Ⅱ Biomechanical testing of a new modified tension band plate for unstable posterior pelvic ringObjectiveTo evaluate the biomechanical stability of posterior pelvic ring fixed with a modified tension band plate, and compare with two iliosacral screws and standard tension band plate. Methods8adult cadaver pelvic specimens (male6, female2, aged from29to54) were used to simulate the AO type C1.2pelvic injury (pubic symphysis diastasis and unilateral sacroiliac joint disruption). Each intact pelvic specimen was firstly tested as a control group before the model of unstable pelvic injury was made. The posterior ring of each pelvis was constructed gradually in randomized order with the following three different implants. The modified tension band plate:a precontoured M-shaped reconstruction plate was used similarly to the standard tension band plate, and a screw was implanted to involved alae sacralis through the plate; The standard tension band plate:the plate was fixed to bilateral posterior superior iliac spines, and the plate at both ends pointed to the pubic symphysis (roughly parallel with the pelvic boundaries); Two iliosacral screws. The anterior pelvic ring of each specimens of was fixed with3.5mm reconstruction plate. All pelvic specimens were placed in the bio-mechanical testing machine in order that a0～600N vertical load and a0～8N·m torsional load were performed. The vertical displacement and torsional angle of the whole pelvic were measured and recorded by the displacement sensors of the bio-mechanical testing machine. The axial stiffness and torsional stiffness of the pelvis were calculated. Under0～600N vertical load, the relative displacement of the sacrum and ilium of the sacroiliac joint in the vertical, horizontal, and anteroposterior direction and the rotation of sacrum relative to the iliac in the sagittal plane were measured and recorded by the prepositioned posterior pelvic ring displacement sensors. Statistical analysis was performed using the analysis of variance test (ANOVA) with repeated-measures for multiple comparisons.ResultsUnder0～600N vertical load, the overall pelvic vertical displacement of the modified tension band plate (2.261±0.383mm) was significantly smaller than the displacement of the standard tension band plate (2.646±0.394mm), the difference was statistically significant (P<0.05). Compared with the two sacroiliac screws (2.144±0.324mm), the overall pelvic vertical displacement of the modified tension band plate was larger than two sacroiliac screw, but the difference was not statistically significant (P>0.05). The overall pelvic axial stiffness of the modified tension band plate was83.1%of the intact pelvis, which increased by12.4%compared to the standard tension band plate (70.7%). The difference between the modified tension band plate and the two sacroiliac screws (87.4%) was not statistically significant (P>0.05). Under0～8N·m torsional load, the overall pelvic torsional angle (2.719±0.507°) of the modified tension band plate was less than the standard tension band plate (3.089±0.472°), and the difference was statistically significant(P<0.05). Compared with the two sacroiliac screws, the overall pelvic torsional angle of the modified tension band plate was larger than two sacroiliac screws (2.608±0.419°), but the difference was not statistically significant (P>0.05). The torsional rigidity of the modified tension band plate is84.8%of the intact pelvis, which increased by10.5%compared to the standard tension band plate (74.3%), and the difference was statistically significant (P<0.05). The difference between the modified tension band plate and the two sacroiliac screws (88.1%) was not statistically significant (P>0.05). Under0～600N vertical load, the displacement of the sacroiliac joint in the vertical, horizontal, and anteroposterior direction and the rotation displacement in the sagittal plane, the two sacroiliac screws was minimum (vertical displacement:0.741±0.164mm, horizontal displacement:0.214±0.031mm, anterioposterior displacement:0.308±0.085mm, sagittal rotation displacement:0.975±0.271°), followed by the modified tension band plate (vertical displacement:0.824±0.183mm, horizontal displacement:0.235±0.030mm, anterioposterior displacement:0.318±0.078mm, sagittal rotation displacement:1.088±0.300°), the standard tension band plate (vertical displacement:1.248±0.205mm, horizontal displacement:0.291±0.034mm, anterioposterior displacement:0.475±0.107mm, sagittal rotation displacement:1.425±0.377°). The difference between the modified tension band plate and the standard tension band plate was significant (P<0.05). Compared with the two sacroiliac screws, the displacement of the modified tension band plate was larger than two sacroiliac screw, but the difference was not statistically significant (P>0.05). The displacement of the standard tension band plate was largest, the difference between the standard tension band plate and the two sacroiliac screws was also significant (P<0.05).ConclusionThe modified tension band plate which is added a screw placed on sacral ala shortens the fixed distance and further mimics the tension band formed by ligaments of the sacroiliac joint complex. Under both vertical and torsional load, the modified tension band plate can offer superior stability for unstable sacroiliac joint than the standard tension band plate, and it is similar to the two sacroiliac screws. It offers a novel and alternative method for the treatment of the unstable sacroiliac joint injury. |
PDF Full Text Request