Possible causes of left inner thigh pain include: high lumbar disc herniation, femoral head necrosis, hip osteoarthritis, ankylosing spondylitis, muscle strain and so on. 1. High lumbar disc herniation: lumbar disc herniation is mostly located in L4-5 or L5-S1 interspace, which is manifested as pain in the waist, buttocks and lower limbs. However, a small number of patients with high lumbar disc herniation, compression of the corresponding high nerve roots can cause pain in the anterior medial thigh or groin area. 2. Necrosis of femoral head: Reduction or interruption of blood supply to the femoral head caused by various reasons can result in ischemic necrosis of the femoral head, and the patient will experience discomfort and pain in the groin, thigh root or buttocks, and the symptom worsens progressively, which can be accompanied by hip joint activity disorder. 3. Osteoarthritis of hip joint: Osteoarthritis of hip joint can be the result of joint degeneration, or secondary to hip dysplasia, fracture, dislocation, and necrosis of the femoral head. Patients mainly show pain in the groin area or buttock area around the hip joint, which can radiate to the thigh or knee joint. 4. Ankylosing spondylitis: Ankylosing spondylitis patients mostly start from sacroiliac joints, which can be manifested as discomfort, soreness and stiffness in the lower back, groin area or buttocks. 5. Muscle strain: excessive hip joint activity can cause thigh muscle strain and thigh root pain, patients usually have a clear history of trauma. It is recommended that patients with thigh pain go to the hospital as soon as possible to find out the cause of the pain and treat it accordingly.