Comparison of different internal fixation models in ankle arthrodesis using 3D finite-element analysis.

BACKGROUND: The purpose of this study is to use three-dimensional finite-element analysis to better understand the biomechanical features of various internal fixators for ankle arthrodesis. METHODS: We used finite-element analysis to compare four different types of internal fixations in ankle arthrodesis: Group A had three crossed screws (Ø6.5 mm); Group B had two crossed screws (Ø6.5 mm) and an anterior plate (Ø2.7 mm); Group C only had an anterior anatomical plate (Ø3.5 mm); Group D had one anterior anatomical plate (Ø3.5 mm) and one posterior-lateral screw (Ø6.5 mm). We adopted Ansys 21.0 software to analyze and compare the four types in terms of the displacement of the arthrodesis surface and the stress peak and stress distribution of these models under intorsion, extorsion, dorsiflexion torque, and neutral vertical load. RESULTS: ① Displacement of the arthrodesis surface: In Group A, the maximum displacement was larger than Group D under neutral vertical load and dorsiflexion torque but less than it under intorsion and extorsion torque. In Group B, the maximum displacement against dorsiflexion, neutral vertical load, intorsion, and extorsion was less than that in the other three fixation models. In Group C, the maximum displacement against the above four loading patterns were significantly higher than that in another three fixation models. ② Stress peak and stress distribution: based on the stress distribution of the four models, the peak von Mises stress was concentrated in the central sections of the compression screws, plate joints, and bending parts of the plates. CONCLUSIONS: The fixation model consisting of two crossed screws and an anterior outperformed the other three fixation models in terms of biomedical advantages; thus, this model can be deemed a safe and reliable internal fixation approach for ankle arthrodesis.

The Treatment Experience of Different Types of Flaps for Repairing Soft Tissue Defects of the Heel.

OBJECTIVE: To summarize the clinical application effects of three different types of flaps for repairing soft tissue defects of the heel, and to discuss the importance of tissue repair and heel reconstruction. METHODS: A total of 46 cases with skin tissue defects of the heel with deep tissue exposure were treated. The reasons for the defect were trauma (n = 26), burns and electric shocks (n = 12), chronic ulcers (n = 2), postoperative infection of the calcaneus and Achilles tendon (n = 5), and tumor resection (n = 1). The scope of wound defect was 2.0×2.5 to approximately 15.0×20.0 cm. The flaps used were medial plantar island flaps (n = 9), distal pedicled sural neurovascular island flaps (n = 23), and free anterolateral thigh (perforator) flaps (n = 14). The flap cutting range was 3.0×3.5 to approximately 16.0×22.0 cm. RESULTS: After surgery, all 46 flaps survived. In two cases, patients experienced partial epidermal necrosis at the distal end of the flap that healed after local dressing exchange, and after this treatment, the complete skin grafts survived. Follow-up was conducted in 40 cases, with an average follow-up duration of 8.2 months (3-44 months) and the two-point discrimination of 5-14 mm. The average American Orthopaedic Foot and Ankle Society scale was 89.2 points with good flap color and texture, satisfactory appearance, and normal gait. CONCLUSION: The repair method should be selected according to the"5-zone method": The plantar medial island flap is suitable for small area (<5 cm) of medial, posterior and plantar defects. The distal pedicled sural neurovascular flap is suitable for lateral, posterior, and medium-range (6-10 cm) joint area defects. The free anterolateral thigh perforator flap is suitable for large-scale (>10 cm) joint area defects.