Quantitative initial safety range of early passive rehabilitation after ankle fracture surgery.

Background: Early rehabilitation training after ankle fracture surgery is critical to healing and avoiding complications. Inappropriate or excessive motion may impede healing or even lead to secondary injury. Currently, there is a lack of scientific quantitative postoperative rehabilitation methods after ankle fracture. Our purpose was to develop a universal method of quantifying early passive rehabilitation training after surgery by finite element (FE) analysis.

Methods: A three-dimensional (3D) FE model of normal ankle was reconstructed from a computed tomography scan of a healthy male adult. Six types of ankle fractures were considered based on AO classification. We exerted joint motion load to explore the effect of movement on ankle joint mechanics after surgery. The corresponding relationship between the Inter-bone displacement and range of motion was measured to quantifying the ankle range of motion. The 44A3.3 fracture was used as an example to describe the implementation process in detail.

Results: During ankle movement, most of the stress was sustained by the internal fixation devices, and the ratio of stress borne by the implants ranged from 67.9 to 94.9%. Flexion/extension exercise did not cause extra stress on the ankle contact surfaces. Ligament traction was the reason for ankle load during flexion/extension motion. The range of early passive postoperative rehabilitation training for six types of ankle fractures (AO classification) were provided.

Conclusion: A quantitative method of early passive rehabilitation training after ankle fracture surgery was developed using FE analysis. This modeling method has universality for any fracture that can be reconstructed.