跟骨舌狀骨折之生物力學研究：有限元素分析

Abstract

跟骨骨折的種類複雜性高，將骨折類型以系統性分類，有助於術前診斷與手術治療的選擇。目前常用分類系統為Sanders和Essex-Lopresti。Essex-Lopresti中的舌狀骨折類型，由於阿基里斯腱連接舌狀碎骨，將影響碎骨的穩定度，對於跟骨舌狀骨折，受到阿基里斯腱造成的生物力學反應是非常值得探討。 跟骨骨折以開放性復位內固定為主要標準的手術方式，但對於使用固鎖螺釘與非固鎖螺釘的固定能力，仍有爭議性。近年來微創內固定手術的研究相當熱門，目前臨床研究認為跟骨舌狀骨折，適合以微創內固定手術治療，但對於骨釘位置的擺放並無共識，因此骨釘植入的固定方法仍有待研究。 本研究將以足部有限元素模型分析Sanders type IIB的舌狀骨折，評估植入物的穩定度與跟骨內部生物力學分析。本研究將分為兩部分：(1)針對開放性復位內固定手術，比較固鎖骨釘與非固鎖骨釘使用於跟骨舌狀骨折的穩定能力；(2)針對微創內固定手術，比較三種骨釘植入位置所造成的差異性。 開放性復位內固定手術的模擬結果中，使用固鎖骨釘與非固鎖骨釘的兩種固定方式，所造成之Bohler’s angle相差均小於1度。微創內固定手術模擬結果中，三種不同骨釘固定方式，造成之Bohler’s angle 相差小於1度。跟骨骨頭在距骨下關節面處均有較高的應力分佈。其中，骨釘由跟骨粗隆上方植入至跟骨骰骨關節面的位置，舌狀碎骨下方有較小的應力分佈，且將碎骨間的應力由舌狀碎骨轉移至跟骨的Anterior process碎骨。 相較跟骨舌狀骨折在開放性復位內固定手術和微創內固定手術兩者而言，其穩定能力相當。開放性復位內固定手術在兩種不同骨釘的選用，均能提供良好的固定能力。微創內固定手術中，對於骨釘不同位置的擺放，會造成跟骨碎骨間的應力分佈差異。

The classification of calcaneal fractures is helpful for the preoperative diagnosis and the decisions of treatment due to the high complexity of types. Nowadays, the most common classification system is Sanders and Essex-Lopresti. In the tongue type fracture of Essex-Lopresti system, tongue fragment connects to the Achilles tendon. The force caused by Achilles tendon may affect the stability of the tongue fragment. Therefore, the biomechanics of tongue type fracture is worth analyzing. Open reduction and internal fixation (ORIF) is a standard surgery for calcaneal fracture, but the stability of fracture fixation between locking and nonlocking screws has been a controversy until now. Recently, minimally invasive techniques using percutaneous fixation (PF) is provoked to reduce these complexity. Because the type of calcaneal fracture is complex and the fixation method of screws is inconsistent, the arrangement of screws must be considered when the calcaneal fracture is treated by PF. The purpose of this study is to use the finite element model to simulate early weight bearing stage in order to evaluate the biomechanical influence and the stability of implant in tongue type. This study will divided two parts: (1) ORIF treatment will compare the stability of the fixation between locking and nonlocking screws. (2) PF treatment will evaluate the difference in three kinds of screws position. In the simulation result of ORIF, the difference of bohler’s angle between locking and nonlocking screws is less than 1ﾟ. Comparably, in the simulation result of PF, the bohler’s angle difference between three kinds of screw positions is less than 1ﾟ. All cases have the high stress on the surface of the subtalar joint. One case of two screws position implanted in parallel from the inferior tuberosity to the posterior facet can transmit the ground reaction force equally and make the less stress on the surface of subtalar joint. The other case of screw position implanted from the superior tuberosity to calcaneocuboid joint has less stress on the inferior tongue fragment. The function of this screw can shift the stress from tongue fragment to the anterior process. ORIF and PF have good stability in tongue type of calcaneal fracture. ORIF with plate using nonlocking or locking screws provided good stiffness and might allow earlier weight-bearing. In the PF, the implanted position of screws might affect the difference of the internal stress distribution between the calcaneal bone fragments.