| Background The sacrum is one of the important structure of the pelvic posterior ring, the incidence of unstable sacral fractures accounted for17%-30%. In pelvic injury,clinically, traumatic spine-pelvic separation often occurred secondary to the type "U"or"H"sacral fracture,the type of "U’sacral fracture is a joint damdge which consist of longiludinal fracture which lie in bilateral of sacrum and the transverse fracture which lie in Denis III, the "U" type of sacral fracture accounting for2.9%of the pelvic fractures,which is relatively rare, it also not in standard classification of fractures of the sacrum to accurately describe the type, the "U"type of sacral fracture is usually has nerve injury,if diagnosis and treat improperly,it can cause nerve progressive dysfunction and and continuous lumbar-sacral pain, in recent years, plenty of evidence has showed that compared with nonoperative treatment, operative can obviously reduce the mortality rate, because this type often has nerve injury, the long-term follow-up results has not yet reached consensus,now,in clinicai, the internal fixation mainly for the type "U" type is sacroiliac screw, nail-bar system,.etc. some studies have shown that the biomechanical strength of sacroiliac screws can be relatively satisfied, but its security channel is narrow, it can easily cause secondary damage of the nerve. With spine-pelvic fixation model has been affirmated and recognized by the most scholars,this technique will be primoted gradually, the nail-rod system is one of the types of spine-pelvic fixation pattern,which treatment is good, but the rod-system used in the treatment of the "U"type sacral fractures can not have enough biomechanics research support, what is more,the corresponding clinical datas are rarely reported.Objective To research the biomechanical strength of the nail-rod system which are used to fix the "U"type of sacral fracture in cadavaric specimen, and the results will be in comparison of sacroiliac screw fixation strength and normal pelvic biomechanical strength, which can supply biomechanical support and theoretical basis for the widely use of nail-rod system to fix the type "U" sacral fracture.Methods The first step:Prepare specimens Take12adult anticorrosive bodies, men six bodies, female six bodies, which were divided into three groups,nail-nod group, sacroiliac screws group and normal pelvic group.Since the L4、5and double leg below the1/3junction cross-sectional bodies, to get12pelvic specimens.The second step:"U" type fracture model established, use fhigh-speed power saws tools to make "U" of the sacrum fracture line, not to destroy the body bone ligaments, retain ties with sacroiliac joints of the ligament in structure and sacrotuberous ligament, sacrospinous ligament, seprate facies auricularis to make the measurement results more actually,The third step:Fracture model fixed:1) nail-rod group:Clear S1pedicle screws site and twist into the screws, strip the soft tissue in the spinailiaca posterior superior, expose the needle points, install Schanz nail,and model form and install the connection rod2) Sacroiliac screws group:Confirm the intersection point in spinailiaca anteriorsuperior and spinailiaca posteriorsuperior the third after the attachment. The hollow drill with the guide bored after the needle, twist into the proper length7.3mm in diameter hollow cancellous screws. The specimens implanted2sacroiliac screws. The Fourth Step:Biomechanics of measurement:All the pelvic specimens are tested with electronic universal test machine,simulated the human body standing posture,and fixed on experimental mechanics machine,then measuring mechanical properties between the sacroiliac screws group、nail-rod group and normal pelvic group. The Fifth Step:Data Statistic Analysis:Measurement data indicated by x±s, Statistics with SPSS13.0statistical software package (version11.5, Chicago, IL, USA), P<0.05for differences with a statistical significance.Results The results of vertical compression load showed axial stiffness, F test analysis showed that there is statistical difference between three groups data, need to compare each other,utimate-load and yield-load of the nail-rod group are larger than the sacroiliac screws group, and the displacement is less than the sacroiliac screws group (P<0.05), there was no statistically significant difference. The three-dimensional movement instrument test results, F test analysis showed that there is statistical difference between three groups data, need to compare each other, show that the angular displacement of nail-rod group is less than normal pelvis, but has no statistically significant difference,in the condition of anteflexion、extension, lateral curvature and rotation, the angular displacement of sacroiliac screws group was larger than the nail-nod group, there has statistically significant difference. Conclusions Compared with sacroiliac screws group, the nai-rod system has Obvious mechanical advantage in axial stiffness, utimate-load and yield-load and displacement, which can provide enough mechanical strength to maintain the normal motion state of the body, also meet fixation strength in the the "U" type of sacrum fracture... |
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