The gap between the femur and tibia joint may be caused by sports injury, degenerative disease, inflammatory disease and other reasons. 1. Sports injuries: frequent hiking, squatting and other sports, may lead to the medial and lateral collateral ligament strain disease, such as fat pad injury or meniscus injury will lead to the femur and tibia joint gap. 2. Degenerative diseases: the gap between the femur and tibia in the elderly is considered to be a degenerative disease, such as osteoarthritis, osteoarthritis joint instability in the late stage, bone spur formation, may stimulate the surrounding joint capsule tissue, and the phenomenon of the femur and tibia joint gap will occur. 3. Inflammatory diseases: Inflammatory diseases such as patellofemoral osteoarthritis or other inflammatory diseases can cause bone spurs around the femur and tibia, instability of the patella, stimulation of the surrounding soft tissues and lead to the femur and tibia joints with gaps. If there is a gap between the femur and tibia, it is recommended that the patient seek medical attention in a timely manner and take appropriate treatment under the guidance of a doctor.