The Biomechanical Evaluation And Clinical Application Of Double Unilateral Static External Fixators With Cross Pins Fixation For The High-energy Injury Of Proximal Tibia Metaphysic

Objective: With the development of communication and building industry, the incidence of high-energy mechanism injury,comminuted fracture always merged with severe soft tissue injury, is on the rising. The high-energy injury of proximal tibia metaphysic is one of the commonest injury, which always associated with high rate of severe complications. As a portion of polytrauma, the treatment has essential difference from those simple closed fractures. As an alternative treatment option for this injury, we choosed a configuration of external fixation which has some advantages as stable, mini invasive and so on. The purpose of this study is to summarize standard application of this external fixation and to explore the effective method in treatment of this kind of disease by the ways of biomechanical evaluation in which 5 different fixation be compared at different loading level in test machine and clinical study in which 26 cases using double unilateral static external fixators with cross pins fixation.Methods: 1 The biomechanical test of 4 different fixation be compared to this frame at different loading level in test machine. The specimen we select fresh freeze focile of donkey instand of embalmed human tibia. Fifteen 4.1.A3 simulated fracture has been done according to the AO/ASIF classification. After devided into three groups random, these simulated fracture was stabilized using the following fixation: unilateral external fixators,double unilateral static external fixators with cross pins fixation,hybrid external fixators,unilateral plates and dual plates. Then each model was loaded cyclically at standard vertical and torsional loading rates on the biomechanical test machine. The data of displacement and torsion angle were recorded and laid in SPSS 11.5 respectively. Statistical analysis was done with methods of one way ANOVA and Student- Newman -Keuls.2 The clinical application From January 2006 to December 2007,30 cases of high-energy injury of the proximal tibia metaphysics were treated with double unilateral static external fixators with cross pins fixation. 26 cases, a total 27 sides were followed up. Of them, 16 sides were open fracture (account for 59.3%). According to Gustilo-Anderson classification, the cases severer than typeⅡrepresent to 65%.11 cases 11 sides were closed fracture(account for 37%),in which approximately 63.6% was occupied by the patients severer than stageⅡbased on Tscherne. Poor soft tissue envelop always merged with comminuted fracture, according to the classification of AO/ ASIF,7 sides were type A2,18 sides type A3 and 2 sides type C2.In them, 3 cases accompanied with rupture of spleen,1 case cerebral trauma and 1 case hemopneumothorax, the fracture of mandible was 2,the number of femur fracture was 10. The duration of fracture union,range of motion and the rate of complication were recorded in full.Results: 1 The results of biomechanical test In the verti- cal loading test, the displacement enlarged with the load increasing. When loading to 600N,the displacement of every group is that 0.397±0.080 mm in the group of unilateral plates,0.144±0.008 mm in dual plate group,2.035±0.071mm in unilateral external fixator group,0.562±0.082mm in the group of double unilateral static external fixators with cross pins fixation and 3.797±1.344mm Hybrid external fixator group. In the torsional test, the torsional angle augmentated with the increasing of torsional moment, when turning to 10Nm,the torsional angle of every group is 26.468±0.420°, 7.527±0.120°, 26.720±0.610°,18.382±0.330°and 26.528±0.500°. Foll- owing the statistical results of S-N-K method, in the vertical loading test, the Mean of double unilateral static external fixators with cross pins fixation,dual plate group and unilateral plate group is 0.562,0.144,0.398,the probability equal 0.529,the null hypothesis was accepted, there is no significent difference according to 0.05 size. Compared to the other two group, significent difference respectively. The torsional test showed that there is no significent difference among unilateral external fixator group,unilateral plate group and Hybrid external fixator group. Compared to the group of double unilateral static external fixators with cross pins fixation and dual plate,there was difference significently.2 The results of clinical application All the patients received 6~20.5 months follow-up, an average of 12.5 months. All cases with good joint function achieved fracture union in 5 months averagely. There were a total of 173 pin sites, 41(account for 23.7%) with reaction or superficial infections and 11 (account for 6.4%)with deep infections. No osteomyelitis and suppurative arthritis emerged. Only one case was discovered tendon injury when he exercise. There is no embolism of deep veins of lower limb detected, no osteofascial compartment syndrome and no excursion of tibia axial line in the process of treatment.Conclusion: 1 The biomechanical test data indicate that this frame of double unilateral static external fixators with cross pins configuration can provide adequate anti-bending stiffness stability and excellent anti-torsion biomechanical properties.2 Because of the following advantages, such as stable, mini invasive, not influence R.O.M, low the incidence of nonunion and the rate severe complication, this kind of method is effective and can be used as last treatment in high-energy injury of proximal tibia metaphysic.