Biomechanical Evaluation of Calcaneal Fracture：Finite Element Analysis

• Main Authors: Chen, Ching-Hsuan, 陳璟璿
• Other Authors: Hung, Chinghua
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/486u8n

博士 === 國立交通大學 === 機械工程系所 === 106 === Calcaneal fractures are the most common fractures of the tarsal bones. The stability of fixation is an important factor for the successful reconstruction of calcaneal fractures. Open reduction and internal fixation (ORIF) with a plate is the standard treatment for displaced intraarticular calcaneal fractures. However, ORIF with an extensive L-incision and fixed with a plate may be complicated by soft tissue issues and wound infection. These complications have led to the development of minimally invasive techniques using percutaneous screw fixation (PSF). For ORIF, the difference in the biomechanical effect between the locking screws and nonlocking screws used remains uncertain. Moreover, secondary arthrodesis is performed more frequently in PSF than ORIF. This means that PSF has to improve its fixation stability for the prevention of traumatic subtalar arthritis and secondary arthrodesis. Calcaneal fracture line patterns and the extent of comminutions can vary greatly. The Essex-Lopresti classification describes the location of the secondary fracture line, producing joint depression or tongue types. The purpose of this study was threefold: First, to analyze the biomechanical influence of plate fixation with different combinations of locking and nonlocking screws through ORIF for treating joint depression and tongue-type calcaneal fractures. Second, this study evaluated the stability differences offered by different PSFs in joint depression and tongue-type calcaneal fractures. Finally, an optimization tool was used to design the optimal screw orientation for improving the stability of PSF. A three-dimensional FE foot model was established, which comprised bones, cartilages, plantar fascia, and soft tissue. Static standing was simulated by applying ground reaction force and Achilles tendon force. To validate this intact foot model, the foot pressure, measured by a force-measuring system, was compared with those calculated from the intact foot FE model. After validation, this model was justified to evaluate the biomechanical influence of ORIF and PSF for calcaneal fractures. Finally, this study used a partial rear foot model for optimization analysis to determine the optimal screw orientations. This definition of the optimization objective function was employed to minimize maximal vertical posterior facet joint displacement. For treating joint depression-type calcaneal fracture with ORIF, this analysis showed that all the locking screws have greater stability than all the non-locking screws. Some hybrid screw configurations generated stability similar to that of all the locking screws. However, ORIF using each kind of screw provided good rigidity for tongue-type calcaneal fractures. This analysis also found that the three types of PSFs in this study all provided greater stability in joint depression or tongue-type calcaneal fractures. In the stress-based analysis, the PP type of PSF, the two screws of which were parallel-inserted from the posterior tuberosity inferior to beneath the posterior facet joint, might moderately alleviate stress between the fragments. In addition, one of the screws in the AS type of PSF for tongue-type calcaneal fracture, which was inserted from the posterior tuberosity superior to the anterior process, might reduce the stress in the tongue fragment. Finally, the analysis of the partial rear foot model showed that the stability of ORIF with different bone qualities was similar. However, the stability of PSF was significantly decreased with the poor bone quality. This study also revealed that the stability of PSF might be improved with the poor bone quality when using the optimization method to design the optimal screw orientation. The results of this study might provide surgeons with useful information for choosing the most appropriate implants for the fixation of calcaneal fractures.