Twelve fresh frozen human ankle specimens with an average age of 57.2±5.1 years (range from 44 to 63 years) were selected and divided into 2 groups with 6 specimens in each group by random number table method. The LARS group was in group A, and the normal ligament group was in group B. The two groups had comparable age distributions. Ankle specimens were frozen at -20°C and thawed for 24 hours at room temperature before use.
Group A: A 3cm arc incision was performed from the anterior and inferior fibula in Group A. The subcutaneous tissue was separated layer by layer to expose the anterior talofibular ligament and the inferior extensor retinoid. Examine all ligaments for visible injury and proper tension, exposing ATFL attachment points on the fibula and talus. The anterior fibular ligament is severed at the fibula attachment. A LARS ligament (LARS®) with a length of around 60mm was produced and marked. A 3.0mm needle was used to drill the fibula tunnel and talus tunnel. The fibula tunnel is placed in the anterolateral fibula at the origin of the anterior talofibular ligament(ATFL), and direction from front down to back up, at a 45°angle to the horizontal line. The talus tunnel was located near the cervical junction of the talus bone, pointing to the tip of the medial malleolus. Make sure the LARS ligament is 20mm long in the talus, fibula, and joint. The LARS ligament was tensioned and fixed with two 3.7mm interference screws (LARS®) after successful installation(Fig 3) . All of the procedures were carried out by a renowned sports medicine surgeon.
Group B: The anterior talfibular ligament and the subextensor retinacular band were exposed in the same manner without the talfibular ligament being cut.
All natural soft tissue was completely removed on the tibia and fibula prior to biomechanical testing. All muscle and soft tissue should be removed. Tibia, posterior talar fibular ligament, calcaneal fibular ligament, and other soft tissue and joint capsule should all be removed. Only the ATFL that has been fixed is kept. In a similar method previously described (20), each specimen was rigorously fixed to a plate with five screws (6mm in diameter), two screws for the instep and two screws for the calcaneus. A 6mm screw was used to secure the subtalar joint. The foot was loaded with 20 degrees of valgus and 10 degrees of flexion relative to the vertical fibula, and all specimens were put on a custom-made steel frame. Two vertical Kirschner pins are used to secure the fibula in a customized model, ensuring that it is perpendicular to the ground during stress(Fig 5). Before the test, the steel frame is finally installed on the test machine. A dynamic tensile test machine was used to conduct biomechanical tests (Motorized PulsE1000, Instrumental Systems, Norwood, MA).
The distance between the fibula and the talus was measured (Instron Systems). The foot is placed in 20°of inversion and 10°of plantar flexion relative to the vertical fibula. To eliminate slack, the sample was prestretched to 5N and then gradually loaded to 15N over 10 seconds. This load was then held for 5 seconds to remove potential creep and then loaded to failure by displacing the fibula at a rate of 20 mm/min. The instrument BlueHill 2 software recorded time, load, and displacement data (instrument system). Excel was used for additional calculations and statistical analysis (Microsoft, Seattle, Washington). According to the load-displacement curve, the final failure load was recorded, the stiffness (N/mm) was computed based on the slope of the curve, and the cause and type of failure were documented.
All analyses were performed using SPSS 20.0 for Windows (SPSS Inc., Chicago, IL, USA), and significance levels were set at P <0.05. All data were normally distributed in Kolmogorov - Smirnov test. Independent T test was used to analyze the differences between groups of maximum failure load and stiffness.
For t tests that demonstrated a statistically significant difference, A post hoc Tukey's honestly significant difference test was conducted to assess the location of the means that were statistically significant between the groups.
Fig5 Left ankle specimen secured in a custom fixture and mounted to the load actuator of a dynamic tensile testing machine before biomechanical testing. The foot is placed in 20°of inversion and 10°of plantar flexion relative to the vertical fibula.