Thigh pain can occur in several areas, anterior, posterior, medial, and lateral thighs, and today I want to talk about pain in the lateral thigh, and I want to analyze whether it is muscle-induced pain or nerve-induced pain. From a muscular point of view: there are no specific muscle groups in the lateral thigh, mainly the broad fascia tensor (iliotibial bundle) is here, which supports the lower limb upright function. If the iliotibial bundle injury its pain is mainly in the buttocks, but can be affected along the lateral thigh to the lateral calf, and the lower and middle 1/3 junction of the lateral thigh is its pressure pain sensitive point, so the pain of the lateral thigh is basically due to the injury of the broad fascia tensor muscle (iliotibial bundle). Contracture of the vastus lateralis muscle: the muscle injury pain is mainly concentrated in the anterolateral aspect of the femoral trochanter, involving pain in the hip joint and extending to the anterolateral part of the thigh, and rarely down the thigh to the lateral knee. It occurs in people who often walk on slopes, sleep with their bodies curled up, or sit with their hips flexed. It is difficult to maintain a sitting position with the hip flexed at 90 degrees or more for long periods of time, and the pain is felt after sitting with the knee flexed for long periods of time. Frequent bending and sitting work with the hip in a flexed position can cause shortening degeneration and aseptic inflammation of the broad fascial tensor muscle. When one side of our waist and hip, knee, calf or ankle cannot walk with weight due to painful lesions, the other leg has to carry the whole weight, so that long-term single-leg weight-bearing can cause strain lesions in the broad fascial tensor muscle on the healthy side. In the case of sudden posterior extension of the thigh and knee extension, it often causes acute injury to the broad fascial tensor muscle, and the broad fascial tensor muscle will contract protectively. When the contracture of the broad fascia tensor is present, it usually persists in small to moderate amounts of activity, but the symptoms worsen at the beginning and at the end, especially when doing body rotation, hip extension and rapid changes in direction of movement. When the condition is relatively severe and prolonged, there is a numbness in the anterior external aspect of the hip, and the pain often radiates along the lateral thigh to the knee area. When the broad fascial tensor is tight, it is difficult for the patient to lean himself against the wall and hyperextend the hip while standing in order to keep the hip in mild flexion. There is no pain when the hip is moved in flexion. When walking with a support, the pain disappears. If the contracture of the iliotibial bundle degenerates, the hip will snap against the femoral trochanter during extension and flexion, resulting in a “snapping hip”. The outer thighs may even become tight, as if the bowstring is tightened, making it difficult to control walking, with the toes pointing outward, resulting in a transverse limp and a crab-like gait. From a nerve perspective, it is lateral femoral dermatomal neuritis. In lateral femoral cutaneous neuritis, although there can also be pain in the lateral thigh, there is more predominantly abnormal sensation, numbness, and decreased skin sensation in the upper and middle part of the lateral thigh. Lateral femoral cutaneous neuritis: pain caused by damage to the lateral femoral cutaneous nerve is a syndrome of abnormal skin sensation and pain in the anterolateral thigh caused by damage to the lateral femoral cutaneous nerve from a variety of causes, mostly in patients of middle age and older. The lateral femoral cutaneous nerve is a sensory nerve that originates from the posterior roots of the lumbar 2 and 3 crestal nerves. After extending from the lateral border of the psoas major muscle, the nerve crosses the deep surface of the iliacus muscle to the anterior superior iliac spine and passes medially below the inguinal ligament to the femoral region. It then descends along the lateral aspect of the suture muscle and travels 5-10 cm from the anterior superior iliac spine to the broad fascia of the thigh and divides into anterior and posterior branches to the anterolateral femoral skin. The etiology of this disorder is complex and often complicated in patients with low back pain because the nerve is compressed at the point of passing through the inguinal ligament or penetrating the broad fascia of the thigh in relation to the pulling, tightening and spasm of the soft tissues in these areas, and the compression factor can be the root cause of the disease. The main symptoms of lateral femoral dermatome neuralgia are unilateral, and the main symptom is abnormal sensation in the anterolateral thigh, such as pain, numbness, burning, stiffness, tingling or bundling. The pain is often tingling, mildly paroxysmal and associated with fatigue and cold; in severe cases, it is persistent and may increase with walking and standing. There are obvious pressure points on the medial aspect of the anterior superior iliac spine and below it, and the skin of the anterior lateral femur can often be examined for hyperalgesia of different sizes and shapes. It is important to draw attention to the fact that the lateral thigh is not innervated by motor nerves and that the sciatic nerve only runs down the posterior side of the thigh and does not pass through the lateral thigh, so when there is pain in the lateral thigh, it should not be identified as sciatica without thinking. Unfortunately, misdiagnosis of this basic common sense often occurs in clinical practice. As long as one is familiar with the anatomy and has knowledge of it, it is easy to differentiate it from the location. In fact, if we take a closer look at the muscles and nerves that cause lateral thigh pain and analyze the relationship between them, it is easy to see that the lateral femoral cutaneous nerve can easily get stuck at the broad fascia, so very often, treating the muscle also has in treating the nerve and treating the nerve also has in treating the muscle, which are complementary and cannot be separated. The source of posterior lateral thigh swelling and pain: sometimes, the location of the thigh soreness and pain is not exactly at the lateral side or directly behind, but is located at the posterior lateral side, that is, the swelling and pressure pain of the biceps femoris muscle, and the semitendinosus and semimembranosus muscles are not affected, which cannot be explained by sciatic nerve or by iliotibial bundle injury. This phenomenon is mostly caused by injury to the femoral square muscle, and it is difficult to find the painful point in the general examination position. In this position, manipulation of the femoral square muscle and the biceps femoris can have an immediate effect. In this patient, a disorder of the fifth lumbar vertebra or a spasm of the sacrospinous muscle on that side can be detected, and if this is treated at the same time, the result will be faster and more stable. The relationship may be that the femoral square muscle is innervated by the sacral plexus branch and the biceps femoris is innervated by the sciatic nerve.