Locking plate fixation for calcaneal fractures of Sanders type IV: a finite element analysis

Abstract

Objective To evaluate the biomechanical performance of a calcaneal locking plate in fixation of calcaneal fractures of Sanders type IV through finite element（FE） analysis. Methods A healthy male volunteer was enrolled for this study who were 26 years old and 70 kg in weight. A 3D FE model of calcaneal fracture of Sanders type IV fixated with a ealcaneal locking plate （Synthes） was reconstructed using software Mimics 13.0 and Geomagic 10. 0 based on the 3D CT images of the volunteer＇s both feet. An axial load of 700 N was applied through the talus. The stress distribution and peak stress of fracture fragments and internal fixator, and the maximum stress point and maximum displacement area of the calcaneus and internal fixator as well, were analyzed. Results The lateral stresses on the calcaneus were concentrated on the 4 areas： the medial side of the subtalar joint （15. 224 MPa）, the bone-screw interface below the subtalar joint （13. 083 MPa）, the bone-screw interface beside the heel （9. 786 MPa） and the bone-screw interface beside the calcaneocuboid joint （7. 632 MPa）. The peek stress on the plate was about 260. 1 MPa, distributed on the fracture line between the posterior fragment and the median-anterior fragment. The maximal displacements occurred on the sustentaculum tali （0. 403 mm）, the interface between the posterior fragment and median fragment （0. 320 mm） and the interface between the anterior fragment and median fragment （0. 319 ram）. The maximal displacement of the plate-screw occurred on the distal side of the proximal screws, especially the one used to fixate the sustentaculum tali, about 0. 390 mm. Conclusions Since fixation with a locking plate for calcaneal fractures of Sanders type IV may lead to a high risk of traumatic arthritis, it is suggested that primary external fixation followed by subtalar fusion be a better choice or appropriate modifications be made of the current locking plate to achieve better mechanical performance. Key words: Calcaneal fracture; Finite element analysis; Computer simulation; Fracturefixation, internal