Knee sprain bending and straightening pain but not painful to touch, may be caused by degenerative osteoarthropathy after sprain, or knee joint wear and tear, infection and inflammation after injury and other factors. 1. Degenerative osteoarthropathy: If a knee sprain is left untreated for a long time, it may cause degenerative osteoarthropathy, which may lead to aggravation of the damage, and then there will be the symptom that it hurts to straighten it out and it doesn’t hurt to press it. 2. Knee wear and tear: if the knee sprain is not treated in time, repeated wear and tear or often do some heavy labor, will lead to different degrees of damage to the knee joint, resulting in knee bending and straightening pain, but not pain when touching. 3. Infection: After a knee sprain is not treated in time, resulting in internal infection and inflammation causing an inflammatory reaction, there may be straightening pain, but no pain when pressed. If you have a sprained knee, you should consult a doctor in time to understand the degree of damage through X-ray examination, and then analyze whether there is an increase in blood by checking the blood routine, and combined with the results of the diagnosis of targeted treatment as prescribed by the doctor.