There are many causes of knee weakness in patients, common causes include trauma, degenerative changes in the knee joint, calcium deficiency, and lumbar spine pathology, as follows: I. Trauma: Patients who suffer trauma to the knee joint, causing meniscal injury, joint capsule injury, fracture, dislocation, or ligament injury, which later requires strict local protective braking, will result in stiffness of the joint and muscle atrophy, thus cause weakness of the knee joint. Second, degenerative changes in the knee joint: such as common knee osteoarthritis, chondromalacia patella, over time will also lead to muscle atrophy, causing weakness of the knee joint. Calcium deficiency: If there is a prolonged calcium deficiency, it will also lead to weakness of the knee joint. Fourth, lumbar spine lesions: patients with lumbar spine lesions, such as lumbar disc herniation, when the compression of the spinal nerve roots, will also lead to weakness of the knee joint.