Characteristic of anterior Pilon fracture and biomechanical mechanisms: a retrospective study and finite element analysis

Background Anterior pilon fractures are generally believed to result from axial loading applied to the foot in a dorsiflexed position. However, the patterns of associated periankle injuries and their underlying biomechanical mechanisms remain unclear. This study aimed to characterize the injury associated with anterior pilon fractures and investigate their potential biomechanical mechanisms using finite element analysis. Methods A retrospective analysis was performed on the clinical data of 51 patients with anterior pilon fractures who were treated at our institution from March 2018 to August 2026. Clinical data, including medical history, imaging examinations, and surgical records, were collected, and fracture patterns were evaluated to identify the morphological characteristics associated with this injury.Based on these findings, a biomechanical hypothesis regarding the occurrence of anterior pilon fractures was proposed.A finite element model of the ankle joint was established to simulate stress distribution and potential injury sites under different loading conditions.The simulation results were compared with the clinical fracture patterns to validate the proposed injury mechanism. Results A total of 51 patients with anterior pilon fractures were included. Among them, talar cartilage (TC) injuries were identified in 18 patients, anterior talofibular ligament (ATFL) injuries in 42 patients, deltoid ligament (DL) injuries in 15 patients, and no calcaneofibular ligament (CFL) injuries were observed.Finite element analysis demonstrated that the Von Mises stress of all evaluated structures generally increased with increasing axial loads from 300 N to 600 N and 1200 N.Among these structures, the stress increases in the DL and ATFL were the most pronounced. The mean stresses of the DL and ATFL increased from 5.52 MPa and 4.39 MPa under a 300 N load to 21.41 MPa and 16.22 MPa under a 600 N load, and further increased to 35.78 MPa and 33.57 MPa under a 1200 N load, respectively.The mean stress of the TC increased from 0.10 MPa at 300 N loading to 4.12 MPa at 600 N and 7.12 MPa at 1200 N.In contrast, the mean stress values of the CFL under the three loading conditions were 1.27, 1.61, and 2.31 MPa, respectively, and remained relatively low throughout.The preoperative VAS score of all patients was 8.2 ± 1.3. No significant pain relief was observed on the first postoperative day, with a VAS score of 7.6 ± 1.5 (P > 0.05). However, the VAS scores at 1 month, 3 months, 6 months, 12 months after surgery, and the final follow-up were 2.96 ± 0.90, 1.87 ± 0.44, 0.94 ± 0.38, 0.83 ± 0.44, and 0.87 ± 0.32, respectively. All values showed statistically significant differences compared with the preoperative score (P < 0.05), indicating that pain levels significantly decreased compared with preoperative values and gradually stabilized during follow-up.The AOFAS score of all patients increased rapidly from 20.1 ± 8.5 preoperatively to 78.5 ± 7.2 at 1 month after surgery.Subsequently, the score showed a continuous and gradual increase, reaching 95.0 ± 3.1 at 6 months after surgery.At the final follow-up, the AOFAS score remained stable at 94.8 ± 3.5. Conclusions Anterior pilon fracture is an intra-articular injury involving the bone–cartilage–ligament complex, and potential occult injuries should be given considerable attention.Ankle arthroscopy facilitates the identification and management of occult injuries.Among these injuries, anterior talofibular ligament (ATFL) injuries and talar cartilage injuries were the most common, followed by deltoid ligament (DL) injuries, while no calcaneofibular ligament (CFL) injuries were observed.Finite element analysis demonstrated significant stress concentration in the anterior talofibular ligament and deltoid ligament, followed by the talar cartilage, whereas the stress in the calcaneofibular ligament remained consistently low.The clinical distribution of injuries and biomechanical analysis collectively suggest that stress transmission, concentration, and local amplification under specific loading conditions may occur during the development of anterior pilon fractures, resulting in the characteristic injury patterns of the ankle joint described above.This study provides a theoretical basis for further understanding the injury mechanism of anterior pilon fractures and optimizing clinical diagnostic and treatment strategies.