The Effect Of Fibular Shortening On Biomechanical Contact Characters In Tibiotalar Joint

Objective: For a long time, clinical doctors usually pay attention to the treatment of tibia and ankle fracture when they deal with the injury of a leg. Hardly a scholar concerns more about the fracture of fibula. Furthermore, fibula is often used as the material of graft harvest and cut without a limit because of diseases. Many scholars thought that if the distal fibula was left, the leg which proceeded a graft harvest will never have any trouble. But, some recent studies found a fibular shortening will lead to a valgus of the talar and the ankle. The patient will have a series of complications, such as instability of the ankle joint and hard in walking, it leads to traumatic arthritis with obviously pain on ankle. Therefore, the treatment of fibular fracture, especially the recovery of the length of the fibula, have been more and more respected recently, however, in what extent the obvious effect on biomechanical characters in the ankle joint will appear is still a question, which is rarely reported in our country. The objective of our study is to evaluate the effect of fibular shortening on biomechanical characters of tibiotalar joint,such as contact area, mean contact pressure and peak contact pressure, with more advanced test methods. It will prescribe the most acceptable extent of fibular shortening and provide reference for clinical surgeon. Methods: Six fresh cadaveric specimens were disarticulated though the knee, and the soft tissues, except for the important ligaments and the ankle joint capsul, were removed from the knee to the level of the ankle joint. Each specimen was fixed to a loading jig. Load was applied to it with the ankle in the neutral position and the subtalar joint was placed in approximately 5 degrees of valgus. A external fixation device was secured to the fibula, then, served at the middle point of the fibula, the fibular shortening model was made by adjusting the external fixation device. The medial malleolus was served, the pressure sensitive film was inserted into the gaps of the tibiotalar joint and the medial malleolus was reduced and fixed. Increasing load was applied through the tibia plateau, at a rate of 25N/s, to the peak value of 700N and last for 1/2 minute. The change of the contact pressure and area in the tibiotalar joint, both in normal and in fibular shortening condition, were measured with the use of the professional instruments and software. Every group of specimen carried out a biomechanical test in the turn of intact, anatomic position, 2mm shortening, 4mm shortening, 6mm shortening. To find the change of the tibiotalar joint after fibular shortening, we took every group of specimen's X-ray imaging of the ankle. The tested pressure sensitive film was divided into four quadrants named as "anteromedial", "posteromedial", "anterolateral"and"posterolateral"; their contact area and pressure were measured and the data was analyzed to draw a conclusion. Results 1. The contact area and pressure of the normal tibiotalar joint: The total contact area is about 284.8±27.3mm2. In the anteromedial quadrant, the contact area is about 77.4±8.3 mm2, the mean pressure is about 2.09±0.46MPa, the peak pressure is about3.24±0.44 MPa. In the anterolateral quadrant, the contact area is about 67.8±6.2 mm2, the mean pressure is about 2.30±0.48MPa,the peak pressure is about3.38±0.47 MPa. In the posteromedial quadrant, the contact area is about 78.1±6.5 mm2, the mean pressure is about 1.73±0.41 MPa, the peak pressure is about2.89±0.38 MPa. In the posterolateral quadrant, the contact area is about 61.5±9.2 mm2, the mean pressure is about 1.87±0.43 MPa, the peak pressure is about3.02±0.41 MPa. 2. The change of the contact area in the tibiotalar joint with the development of the fibular shortening: Through the test, we found that, compared with the intact specimen, the total contact area of the tibiotalar joint tended to decrease in the fibular shortening model; from 4 mm fibular shortening, the value had displayed a statistical difference (p<0.05); and from 2 mm fibular shortening, the mean contact area in every quadrant tended to have a redistribute. With the development of the fibular shortening, the contact area in anteromedial quadrant and posteromedial quadrant tended to decrease, while,in anterolateral quadrant and posterolateral quadrant, they tended to increase. Furthermore, the change in the anteromedial quadrant and posterolateral quadrant was particularly significant, from 2mm fibular shortening, they had shown a statistical difference (p<0.05). 3. The change of the contact pressure in the tibiotalar joint with the development of the fibular shortening: Through the measurement of the pressure, we found that with the development of the fibular shortening, comparing with the intact specimen, the contact pressure of the different quadrants in tibiotalar joint displayed a significant change. The mean contact pressure and peak contact pressure in anteromedial quadrant and posteromedial quadrant tended to decrease, while, in the anterolateral quadrant and posterolateral quadrant, the value tended to increase. Moreover, the change in the anteromedial quadrant and posterolateral quadrant was particularly significant, from 2mm fibular shortening, they had shown a statistical difference (p<0.05). 4. The result we found in the X-ray imaging of the ankle: We found that fibular shortening will lead to the lift of lateral malleolus, the widening of the talus'dome and the lateral shift of the talus. Because of the pull of the lateral collateral ligament, the talar tended to have a valgus and the medial gap of the tibiotalar joint became wider., while the lateral gap became narrower. We have identified that with the study of the X-ray imaging of the ankle.