The importance of Böhler’s angle in calcaneus geometry: A finite element model study

Abstract

Objectives: Calcaneal fractures are the most common tarsalfractures following a foot-ankle trauma. The Böhler’s angle is animportant measurable angle before, during, and after surgery. Inthis study, we aimed to investigate correlation between Böhler’sangle, calcaneal strength, and subtalar joint stress using a finiteelement analysis (FEA).Patients and methods: Between January 2016 and December2016, computed tomography (CT) scans were used with MIMICS®software for FEA. The ankle and foot of a 23-year-old maleperson with a height of 180 cm and weighing 80 kg was modeledas reference. Raw coronal CT images were obtained in DigitalImaging and Communications in Medicine format with theresolution of 512¥512 pixels and 0.3-mm slice intervals in 135 kV.The structures including tibia, fibula and 26 other bones (talus,calcaneus, cuboid, navicular, three cuneiforms, five metatarsals,and 14 components of phalanges), cartilage and ligamentoustissues were modeled to form ankle joint. After determiningBöhler’s angle as 35 degrees for the reference model, a fractureline was created on calcaneus. Calcaneus was remodeled with theBöhler’s angle of 45, 40, 30, 25, 20, 10, and 0 degrees respectively.All models were transferred to ANSYS software for FEA and theloads on the lower extremities with normal posture were appliedon models.Results: Analysis of all models based in the reference modelrevealed that maximum tension values on calcaneus increased,while the Böhler’s angle decreased, indicating a statisticallysignificant difference. The decreased Böhler’s angle indicatedstatistically significantly higher maximum tension values (p=0.04).Action force in subtalar joint was evaluated by comparing withthe forces in reference model. The increased Böhler’s angle wasfound to be associated with statistically significantly decreasedamount of load on subtalar joint. The decreased Böhler’s anglewas related to the statistically significantly increased amount ofload on subtalar joint.Conclusion: Our study results suggest that decreased Böhler’sangle increases the possibility of subtalar arthrosis, althoughovercorrection of the Böhler’s angle seems not to increase the riskof subtalar arthrosis.