The length of the lower extremity can be measured by the following methods: first, measuring the distance between the anterior superior iliac spine and the tip of the medial or lateral ankle. Second, the distance between the greater trochanter of the femur and the tip of the inner or outer ankle is measured. By measuring the length of the lower extremities, it is possible to observe whether both lower extremities are symmetrical, whether there is lateral pelvic tilt, and even indirectly reflect lumbar scoliosis. If a fracture or femoral head necrosis has occurred in the lower extremity, measuring the length of the lower extremity can determine the choice of prosthesis for surgery and can ensure that both lower extremities are symmetrical after surgery. Therefore, the measurement of the lower extremity length is crucial, and any deviation in the measurement may affect the post-surgical results, and patients may even experience serious consequences such as bilateral lower extremity asymmetry and limb claudication.