What is the hip joint? The hip joint consists of the acetabulum and the femoral head, which is a multi-axis ball and socket joint connecting the trunk and lower extremities, surrounded by the strongest muscles and ligaments in the body. The acetabulum is composed of the iliac bone, pubic bone and sit bones, which is commonly known as the “hip bone”. (Figure 1) Figure 1 Femoral head: the upper end of the femur facing inwards and upwards, spherical in shape, associated with the acetabulum. The femoral head is the spherical end of the “big stick bone” of the animal we normally eat. (Figure 2) Figure 2 Because the hip joint is the deepest joint in the human body, the acetabulum is so far forward and downward that it almost completely covers the head of the femur, which is very similar to the mortar and pestle tool used by ordinary people to pound grain or medicine. Therefore, it is also regarded as the most typical and perfect “mortar and pestle joint” in the human body. The “pestle” is equivalent to the femoral head of our hip joint, while the “socket” is equivalent to the acetabular part of our hip joint (Figure 3). Figure 3: Analogy between the pestle and the hip joint This form of construction is also designed to accommodate the weight-bearing needs of the lower extremity, and the deeper fossa makes the hip joint more stable, which is the opposite of the upper extremity, which requires more flexibility, and therefore the “head” of the shoulder joint is larger than the “socket”. “This is in contrast to the upper extremity, which requires more flexibility. As a result, the shoulder joint is more mobile, while the hip joint is more stable. In addition, there are as many as 20 muscles that act around the hip joint, and they play an important role in ensuring the mobility function of the hip joint. The hip capsule and surrounding ligaments work together to ensure the stability of the hip joint. What is the function of the hip joint? The hip joint is a multi-axis joint that can flex, straighten, abduct, adduct, internally rotate, and externally rotate. Although its mobility is not as extensive as that of the shoulder joint, it plays an extremely important role in supporting the body and lower limb activities such as walking, running and jumping, especially when people exercise, whether it is running, apparatus, aerobics, etc. It plays a pivotal role. The following figure shows the range of motion of the hip joint in a normal person. (Figure 4) Figure 4 (from the fourth edition of Practical Orthopedics) When there is a hip joint lesion, it is often accompanied by a change in the range of motion of the hip joint, with different degrees of limitation of movement. You can check yourself to see if you can perform the various movements in the above figure. When hip pain occurs, if it is accompanied by difficulty in squatting, you should be alert to the presence of hip joint disease, and some patients will also be unable to “stilt”, leg can not be outward, etc., you should go to the hospital as soon as possible to exclude hip joint disease. What are the forces on the hip joint? How to protect the hip joint? The hip joint is the weight-bearing joint of the lower limbs. In different states of the body, the hip joint is subjected to different forces throughout the body: 1, in a quiet single-leg stand, the force transmitted through the hip joint is 2-2.8 times the body weight; 2, when standing on both legs, the force on a single hip joint is about half of the force when standing on one leg; 3, when walking, the force on the hip joint is 3 times the body weight; 4, when going up stairs, it is 10 times the body weight, and when going down stairs, it is 20 times the body weight. weight, 20 times the weight when going down the stairs; 5. 1.2 times the weight of the hip when riding a bicycle. Speaking of this, we should be able to see that we should try to avoid single-leg weight bearing, and cycling is a relatively favorable exercise for the protection of our hip joint, in addition, downstairs than upstairs hip joint is more strain, more likely to aggravate the injury. Understanding these, I believe that we will choose a more good lifestyle according to our own situation and protect our hip joint.