Sudden pain in the knee can not walk may be caused by trauma, lumbar disc herniation, arthritis and other reasons. 1. Trauma: due to strenuous exercise, fall, impact and other traumatic injuries caused by the knee joint medial and lateral, cruciate ligament strain or meniscus tear or fracture around the joint, the patient may appear to have a sudden onset of pain, can not walk and other symptoms. 2. Lumbar intervertebral disc herniation: mostly due to the acute stage of lumbar intervertebral disc herniation or external force, causing acute herniation to compress or stimulate the nerve root, resulting in sudden onset of radiating pain in the knee area, inability to walk and other symptoms. 3. Arthritis: including rheumatic, rheumatoid, osteoarthritis, gouty arthritis and other diseases, the patient in the activity or cold, causing local inflammation aggravation which leads to the patient suddenly appeared knee pain, can not walk symptoms. Sudden pain in the knee can not walk may also have other reasons, it is recommended that patients go to the hospital in a timely manner to improve the examination, to clarify the specific causes of the disease, according to the condition of the further treatment.