Biomechanical analysis of hip-knee joint impact injury in typical postures

Hip and knee soft tissues are susceptible to different forms of impact injury risk in typical postures, the biomechanical mechanism of hip-knee joint impact injury is not clear yet. We developed a multi-flexible body finite element model for human unilateral hip-knee joint to study the impact injury patterns and biomechanical characteristics. Based on the CT and MRI images, a biomechanical finite element model of the hip-knee joints was established with soft tissues at different flexion angles. The biomechanical characteristics of the hip-knee joints and the risk of the soft tissues impact injuries are investigated under different impact loading conditions. The total displacement and total stress of the hip and knee joints were basically the same under point and surface impact loading conditions; Under four impact locations such as femoral midshaft, knee joint, proximal third tibial region, and proximal third fibular region, relative to the upright position, the overall increase in displacement at 30° flexion position of the hip-knee joints was 128%, 60.7%, 82.6%, and − 77%, and the increase in stress was 36.8%, 11.0%, 55.9%, and − 67.3%, respectively. In the seated position (90° flexion), the stresses in the acetabular cartilage and hip bone decreased as the longitudinal impact angle increased. The stresses and displacements in the hip bone and acetabular cartilage peaked at the − 10° transverse impact angle. The biomechanical risk of human unilateral hip-knee joint injuries in different impact patterns and typical flexion postures was investigated for hip-knee joint protection.