Static finite element analysis of the stability of osteotomy after hallux valgus surgery based on wrapped curtain method with external fixation

BACKGROUND: Integrated Traditional Chinese and Western Medicine minimally invasive treatment for hallux valgus based on wrapped curtain method with “8”-shaped bandage and sub toe pad external fixation has been used for a long time in the clinic. This method abandons the internal implant fixation and external plaster fixation. After surgery, patients could take care of themselves. However, the activity of the broken end may cause fracture nonunion, which once aroused scholars’ question. Recently, with the continuous improvement of foot biomechanics research, foot finite element model and applications become a reality. OBJECTIVE: To evaluate the stability of osteotomy after the operation of wrapped curtain method with “8”-shaped bandage and sub toe pad external fixation on the basis of static finite element method. METHODS: A young female volunteer with hallux valgus was selected, whose body weight was 58 kg, and right foot hallux abductor valgus angle was 24°; intermetatarsal angle was 13°; proximal articulator set angle was 7°; distal articulator set angle was 7°. CT was used to scan the right foot. ABAQUS software was applied to establish a finite element model of right foot hallux valgus bone, and model of the first metatarsal neck minimally invasive osteotomy was simulated based on wrapped curtain method with external fixation. Von Mises stress and displacement at the osteotomy end were calculated. RESULTS AND CONCLUSION: (1) The maximum stress was 0.067 MPa without external fixation, and the maximum stress was 1.258 MPa with the external fixation. Stress was mainly distributed in the outer edge of the osteotomy. (2) The maximum absolute displacement was 0.363 mm without external fixation, and the maximum absolute displacement was 0.716 mm with external fixation. The two largest displacements were both in the Z-axis direction. Statistical analysis confirmed that the four nodes absolute displacement and stress were significantly different (P < 0.01). (3) The maximum relative displacement was 0.101 mm. The maximum relative displacement was 0.046 mm with external fixation. The maximum relative displacement without external fixation was 0.102 mm and occurred in the Z-axis. The maximum relative displacement with external fixation was 0.110 mm and occurred in the Y-axis. (4) One-way analysis of variance confirmed that the four nodes relative displacements were not statistically significant in X-axis and Y-axis (P > 0.05). The four nodes relative displacements were statistically significant in Z-axis (P < 0.05). (5) These findings suggest that the external fixation based on wrapped curtain method after hallux valgus surgery could effectively reduce osteotomy displacement. The moderate stress and elastic fixation are conducive to fracture healing.