Finite element analysis of the effect of sagittal angle on ankle joint stability in posterior malleolus fracture: A cohort study

Objective: Aim of this study was to establish three-dimensional finite element model of the posterolateral-oblique type of posterior malleolus fracture with different sagittal angle and to explore the effect of sagittal angle on ankle joint stability. Methods: CT data of ankle were collected from a normal male volunteer. Established finite element model of the normal ankle and verified its reliability. Five posterior malleolus fracture models with different sagittal angles were established. Finite element analysis(FEA) was carried out to simulate the conditions of vertical loading in neutral position with a total weight of 600 N. Recorded the data and did statistical analyses. Results: (1) The contact area was 483.55 mm2 and the maximum contact stress was 3.793 MPa in the model of the normal ankle joint. (2) There was a positive correlation between the sagittal angle(SA) and the contact area (CA)(r = 0.925, P < 0.05). Regression equation was CA = 316.755 + 1.749*SA. The correlation between the sagittal angle and the maximum contact stress(MCS) was negative (r = -0.988, P < 0.01). Regression equation was MCS = 5.214-0.018*SA. There was a negative correlation between the sagittal angle of fracture and relative displacement(RD)(r = -0.950, P < 0.05). Regression equation was RD = 1.388-0.009*SA. Conclusion: The greater the sagittal angle of fracture was, The more stable the ankle joint was. The sagittal angle of fracture could be used as a relative index to reflect ankle stability for posterior malleolus fracture.