下胫腓联合损伤三种内固定方式稳定性重建生物力学评价

Biomechanical Evaluation for the Stability Reconstruction of Ankle Joints with Distal Tibiofibular Syndesmosis Injury via 3 Different Internal Fixation Methods

目的观测下胫腓联合损伤采用一枚螺钉、两枚螺钉或加1/3管型钢板固定稳定性重建的生物力学性能,为临床选择有效内固定提供理论依据。方法采集6具新鲜成人下肢尸体标本,制成正常组(N)、损伤组(I)和固定组,固定组固定方式包括下胫腓联合损伤复位后分别用1枚螺钉固定(A1)、2枚螺钉固定(B1)、2枚螺钉加1/3管型钢板固定(C1)等三种固定方式,行生物力学实验应力分析,模拟足运动中立位、跖屈位(30°)、背屈位(20°)、旋后外旋位等4种运动工况,测量踝关节的强度、刚度和稳定性。结果 1下胫腓联合损伤后,在4种运动工况下,踝关节的强度、刚度发生异常变化,内外踝应力强度分别下降21%,39%,前后踝穴处,应力强度分别下降29%和35%;轴向压缩刚度(EF),水平剪切刚度(GF)分别减少27%和28%,与正常标本(N)比较差异有统计学意义(P<0.05);2下胫腓联合复位后,三种内固定方法均能够使踝关节恢复到正常稳定状态,踝关节的应力强度均超过正常组,其中A1组与正常组(N)差异无统计学意义(A1/N,P>0.05),而B1、C1组与正常组(N)差异有统计学意义(B1/N,C1/N,P<0.05),但两组间差异无统计学意义(P>0.05);踝关节的轴向压缩刚度(EF)、水平剪切刚度(GF)三组均超过正常组(N)差异有统计学意义(A1/N,B1/N,C1/N,P<0.05),B1与A1比较,EF、GF平均增加14%和15%,B1与C1相比,两组差异无统计学意义(P>0.05)。结论一枚螺钉三皮质固定(A1组)的力学性能更接近正常组,而后两种固定则更为坚强。但坚强的固定会使踝关节对关节活动的顺应性下降,而使螺钉所受的应力增加,易产生螺钉的松动或疲劳断裂。

Objective To investigate the biomechanics of the stability reconstruction of ankle joints with distal tibiofibular syndesmosis injury by means of three cortical single screw, three cortical two screws or three cortical two screws plus 1/3 tube type plate fixation, in order to provide a scientific basis for clinical selection of effective internal fixation method. Methods Lower limbs from 6 fresh adult cadaver were used to make standard ankle in-jury models and then were divided into normal group, distal tibiofibular syndesmosis injury group, fixation with three cortical single screw group（A1）, fixation with three cortical 2 screws group（B1）, and fixation with three cor-tical 2 screws plus 1/3 tube type and plate fixation group （C1）. The load was applied on tibiofibular bone of the shank to simulate the 4 physiological movement of the foot, i.e. neutral position, plantar flexion（30o）, dorsal flexion （20o）, and supination external rotation, and the strength, stiffness, and stability of ankle joint were measured after-wards. Results After the distal tibiofibular syndesmosis injury, the strength and stiffness of the ankle joint signifi-cantly decreased compared to normal group： the stress intensity of the medial and lateral malleolus reduced by 21% and 39%, respectively; the stress intensity of the anterior and posterior malleolus decreased by 29% and 35%,respectively; the EF and GF reduced by 27% and 28%, respectively（all P〈0.05）. The ankle joint after syndesmotic restoration with A1, B1 and C1 methods successfully gained stability; the stress intensity in A1 group was not sig-nificantly different from that in normal group （P〉0.05）, and that in B1 and C1 groups were significantly higher than that in normal group（P〈0.05）, but no significant difference was found between the former 2 groups（P〉0.05）. The EF and GF in A1, B1, and C1 groups were higher than that in normal group （P〈0.05）. The EF and GF in B1 group increased by 14% and 15% compared with those in A1 group （P〈0.05）, while no significant difference was found between B1 group and C1 group （P〉0.05）. Conclusion The fractured ankle treated with three cortical single screw fixation has similar mechanical properties to normal ankle, and those treated with other 2 methods have more strength. Too much strength may lead to decrease of joint activity compliance and stress increase, result-ing in screw loosening or fatigue fracture of the ankle syndesmosis.