RESUMEN
Objective:To determine the relationship between tibial plateau stresses and malunion by exploring the changes in mechanical conduction in the knee joint after malunion of Hoffa fracture of the tibial plateau.Methods:This study selected 28 knee joint specimens treated with formalin for preservation, half of which were from male and half from female individuals with an age of (51.4±9.5) years. Their structures were intact, and flexion-extension activities normal. X-ray examinations excluded osteoporosis, tuberculosis, and diseases that could have potentially affected bone quality. The knee specimens were divided into a control group (intact tibia) ( n=4) and 6 groups of tibial plateau Hoffa fracture malunion model: 3 vertical malunion groups (groups V1, V2, and V3, with a vertical displacement of 1, 2, and 3 mm, respectively, n=4) and 3 separation malunion groups (groups S3, S5, and S7, with a separation displacement of 3, 5, and 7 mm, respectively), with half males and half females in each group. After a 600N vertical load was applied at passive knee flexions at 0°, 30°, 60°, 90°, and 120°, the stress levels in the medial and lateral compartments of the knee joint were measured using pressure-sensitive films. Results:Under a vertical load of 600 N, when the knee joint was in a neutral position (flexion of 0°), the differences in the medial and lateral tibial plateau stress values were not statistically significant between the malunion models groups and the control group ( P>0.05). When the knee flexion increased to 30°, the medial tibial plateau stress in the V3 and S7 groups was significantly greater than that in the control group ( P<0.05). At a knee flexion of 60°, the medial plateau stress was significantly greater in the V3, S5 and S7 groups than that in the control group, and the differences were significantly greater than the comparisons at a knee flexion of 30° (all P<0.05). When the knee flexion was 90°, the medial plateau stress in the V2, V3, S5 and S7 groups was significantly greater than that in the control group ( P<0.05), but the lateral tibial plateau stress in the V3 group was significantly smaller than that in the control group ( P<0.05). When the knee flexion was further increased to 120°, the differences in the medial and lateral plateau stress values were statistically significant between all the malunion groups and the control group ( P<0.05), and the differences significantly greater than the comparisons at a knee flexion of 90° (all P<0.05). Under a vertical load of 600 N, the differences in the stresses on the medial and lateral plateaus were not statistically significant between the control group and all the malunion groups at a knee flexion of 0° ( P>0.05). When the knee flexion increased to 30°, the difference between the medial and lateral stresses was not statistically significant in the control group ( P>0.05), but was statistically significant in the V3 and S7 groups ( P<0.05). When the knee flexion reached 60°, 90°, and 120°, the differences between the medial and lateral tibial plateau stresses in all the groups were statistically significant ( P<0.05). Conclusions:The peak knee stresses after malunion of Hoffa fracture of the tibial plateau correlate with the severity of malunion and knee flexion angles. The mechanical properties are not significantly different between a mild malunion knee and a normal knee, but a significant displacement (vertical displacement >2 mm and separation displacement ≥5 mm) may increase the peak knee stresses to increase the risk of knee osteoarthritis. When the severity of malunion is certain, an increase in knee flexion angle increases the difference in the peak stress between the medial and lateral tibial plateaus, thus increasing the risk of knee osteoarthritis.