Hidden pain in the left thigh root may be related to physiological factors such as long time walking and overwork, or pathological factors such as hip arthritis, synovitis and necrosis of femoral head. 1. Physiological factors: due to long time walking, overwork and other factors, can lead to the thigh root of the soft tissues of the tension strain, the accumulation of lactic acid in the body, can cause the left thigh root hidden paroxysm of pain, belong to the normal physiological phenomenon, can be gradually relieved after rest. 2. Hip arthritis: Hip arthritis is a degenerative disease of the hip joints, causing damage to the soft tissues around the joints, inflammatory stimulation will lead to pain in the hip joints, and the symptoms will be aggravated by activities, accompanied by limitation of hip joint activities. 3. Synovitis: synovitis is an inflammatory change of synovial membrane caused by trauma, infection, tuberculosis and other factors. If synovitis occurs in the hip joint, it will lead to local soft tissue pain, swelling and limitation of joint activities. 4. Necrosis of femoral head: Necrosis of femoral head refers to the damage or interruption of blood supply to the femoral head leading to the death of bone marrow or bone cells, which will cause the collapse and structural change of the femoral head, causing pain in the hip joint and groin area. The left thigh root always hidden pain may have other causes, it is recommended that the patient timely hospital consultation, clear causes for targeted treatment.