有限元法分析不同固定方式在胫骨远端粉碎性骨折骨愈合中的生物力学差异

Biomechanical difference of different fixation methods in bone healing of distal tibial comminuted fractures analyzed by finite element method

背景:胫骨远端粉碎性骨折伴软组织损伤的治疗具有挑战性,新型逆行胫骨髓内钉、外置接骨板是重要的治疗手段,但其在骨折愈合不同时期、不同负重情况时的骨折端应变、应力遮挡情况未见报道。目的:通过有限元分析法探讨骨折愈合不同时期逆行髓内钉及外置接骨板的生物力学差异,为临床应用及康复锻炼提供科学参考。方法:利用1名40岁健康男性的胫骨CT数据,建立胫骨远端粉碎骨折的有限元模型,构建胫骨逆行髓内钉、外置接骨板固定模型及骨痂模型并根据骨折的固定原则进行装配。使用ANSYS软件进行有限元分析,比较骨折愈合不同时期时逆行髓内钉及外置接骨板2种固定方式的骨折端位移、胫骨应力遮挡、骨痂应力、胫骨及固定装置应力分布情况。结果与结论:①胫骨骨折端相对位移随着骨折愈合的进行逐渐减小,在术后3个月后位移明显减少;术后0,1个月,外置接骨板组的垂直位移及总位移均大于逆行髓内钉组,2种固定方式的Z轴位移(水平内外侧位移)均较X、Y轴位移明显,且接骨板模型的Z轴位移差异最明显;2种固定方式的Z轴位移最大位置均位于胫骨外侧,位移最小位置均位于胫骨内侧;②骨折愈合的应力遮挡率随骨折时间延长而逐渐降低;逆行髓内钉的应力遮挡率在骨折愈合不同时期均高于外置接骨板;术后3个月后外置接骨板的应力遮挡率降低到4%左右,逆行髓内钉的应力遮挡率降低到40%左右;③2种固定方式骨痂应力集中部位的应力随着载荷的增大而增加,外置接骨板组骨痂的应力始终大于逆行髓内钉组;2种固定方式中,骨痂最大应力大致分布一致,均位于胫骨外侧部分;④随着骨折愈合2种固定方式的胫骨最大应力逐渐降低,外置接骨板组的应力始终大于逆行髓内钉组;1500 N载荷下外置接骨板组胫骨最大应力区域平均应力为285 MPa,而逆行髓内钉组为26 MPa;⑤随着骨折愈合2种固定模型中固定装置的应力逐渐降低,外置接骨板组的应力均明显高于逆行髓内钉组;术后3个月以后,2种固定装置的应力下降幅度明显变缓;⑥提示在骨折愈合早期,胫骨逆行髓内钉组中骨折端应变小、胫骨最大应力适中,允许早期负重;外置接骨板组骨折端存在应变过大、胫骨最大应力过大,需在保护下部分负重、不能完全负重;在骨折愈合中后期,胫骨逆行髓内钉及外置接骨板组均可完全负重,接骨板的应力遮挡率明显低于胫骨逆行髓内钉。

BACKGROUND:The treatment of distal tibial comminuted fractures with soft tissue injury has always been challenging.The new retrograde tibial nailing and supercutaneous locking plate are important treatment methods,but their strain and stress shielding at the fracture end during different periods of fracture healing and different load conditions have not been reported.OBJECTIVE:To explore the biomechanical stability of retrograde tibial nailing and supercutaneous locking plate in different periods of fracture healing by finite element analysis to offer a scientific foundation for clinical application and rehabilitation exercise.METHODS:The finite element model of distal tibial comminuted fracture was established by utilizing the CT data of the tibia from a 40-year-old healthy male.Retrograde tibial nailing,supercutaneous locking plate,and callus models were assembled in accordance with the principle of fracture fixation.The finite element analysis was performed using ANSYS software to compare the displacement of the fracture end,the stress shielding of the tibia,the stress of the callus,and the stress distribution of the tibia and the fixation device during different periods of fracture healing.RESULTS AND CONCLUSION:(1)The relative displacement of the tibial fracture decreased gradually with the healing of the fracture,and the displacement decreased significantly after 3 months.At 0 and 1 months after operation,the vertical displacement and total displacement of the supercutaneous locking plate group were higher than those in the retrograde intramedullary nail group.The Z-axis displacement(horizontal medial and lateral displacement)of the two fixation methods was more obvious than the X-axis and Y-axis,and the Z-axis displacement of supercutaneous locking plate group was the most obvious.The maximum Z-axis displacement of the two fixation methods was located on the outside of the tibia,and the minimum displacement was located on the inside of the tibia.(2)The stress shielding rate at different periods of fracture healing gradually decreased with time.The stress shielding rate of the retrograde intramedullary nail was higher than that of the supercutaneous locking plate at different stages of fracture healing.After 3 months,the stress shielding rate of the supercutaneous locking plate was reduced to about 4%,and the stress shielding rate of the retrograde intramedullary nail was reduced to about 40%.(3)The stress of the stress concentration site of the callus in the two fixation methods increased with the increase of the load,and the stress of the callus in the supercutaneous locking plate group was always greater than that in the retrograde intramedullary nail group.The maximum stress distribution of the callus was approximately equally distributed among the two modes of fixation,both in the lateral portion of the tibia.(4)As the fracture healed,the maximum stress of the tibia in the two groups decreased gradually,and the stress in the supercutaneous locking plate group was always greater than that in the retrograde intramedullary nail group.The average stress of the maximum stress area of the tibia in the supercutaneous locking plate group under 1500 N load was 285 MPa,while that in the retrograde intramedullary nail group was 26 MPa.(5)As the fracture healed,the stress of the fixation device in the two groups decreased gradually,and the stress in the supercutaneous locking plate group was significantly higher than that in the retrograde intramedullary nail group.After 3 months,the stress of the two fixation devices decreased significantly.(6)It is indicated that in the early stage of fracture healing,the strain on the fracture end in the retrograde intramedullary nail group is small,and the maximum stress of the tibia is moderate,allowing early loaded.The fractured ends in the supercutaneous locking plate group had too large strain and too large maximum stress of the tibia,which needed to be partially loaded under protection and could not be fully loaded.In the middle and late stages of fracture healing,the tibial retrograde intramedullary nail and the supercutaneous locking plate could be completely loaded,and the stress shielding rate of the supercutaneous locking plate was significantly lower than the tibial retrograde intramedullary nail.