Comparison of stress distribution between normal and malunion calcaneus

Objective To compare the stress distribution of calcaneal compression articular surface and normal surface in biomechanical analysis.Methods The posterior articular facet of the normal finite element model was wedged resected from inside to outside and from front to back,to imitate the malunion model with subtalar articular surface collapse after fracture.The B(o)hler angle was 35° before wedged,and 0° after wedged.On heel and Achilles tendon attachment point,320 N and 160 N loads were applied vertically upwards respectively.Compare calcaneal Vonmises stress distribution between malunion and normal model.Results Judging from the general stress distribution of malunion of calcaneal,subtalar joint stress reduced.The main stress area of normal bone joints was in articular surface,while the main stress area of malunion model was in the lateral calcaneal close to the calcaneocuboid joint.The main stress of the outboard is high-er than that of inboard.Outboard is the main part of supporting load.Judging from the detailed comparison with bone structure,first of all,the subsidence of subtalar joint top resulted in partial backward of the main stress of the calcaneus,which shifted to the Achilles tendon attachment point.It increased from normal (1.51±0.22) MPa to (3.11±0.24) MPa.Joint top of the stress reduced from normal (6.71±0.37) MPa to (2.83± 0.49) MPa.Secondly,the calcaneus stress of the former calcaneocuboid articulation significantly increased,which increased from normal (0.46±0.15) MPa to (2.13±0.15) MPa,and sustentaculum tali stress decreased from 5.18 MPa to 1.41 MPa.Conclusion By finite element model of this subject,the study proves that subtalar joint surface collapsed in calcaneal fractures is the main causes of most pathological changes.The problem of the joint surface subsidence should be resolved firstly in a clinical treatment,and the normal height of the calcaneus should be restored.The internal stress distribution of calcaneal is essential to the pain in the related part of calcaneal. Key words: Finite element analysis;  Calcaneus;  Fracture healing;  Stress, mechanical