What Is the Acetabulum?

The hip joint is one of the largest and most stable joints in the human body, and is a typical ball and acetabular joint. The hip joint has both good internal stability and flexible mobility.

The hip joint is one of the largest and most stable joints in the human body, and is a typical ball and acetabular joint. The hip joint has both good internal stability and flexible mobility.

Chinese name

Acetabulum

Foreign name

acetabulum

Make up

Sit, sit, shame

Department

head

Anatomical features and kinematics of acetabulum

The acetabulum is located in the center of the outer side of the hip bone, and is semi-spherical deep concave, with a diameter of about 30-50 mm, and the surface is covered with transparent articular cartilage with a thickness of about 2 mm. In the center is the acetabular fossa, which is not covered by cartilage. It is filled by the Harvard gland. It can be squeezed out or inhaled as the pressure in the joint increases or decreases to maintain the pressure balance in the joint. The circular glenoid labrum at the edge of the acetabulum can deepen and widen the acetabulum, so that the acetabulum can accommodate the large part of the femoral head and is in a stable position, which strengthens the stability of the hip joint.

The main activities of the hip joint can be decomposed into three mutually perpendicular planes: flexion and extension on the sagittal plane, adduction and abduction on the coronal plane, and internal and external rotation on the transverse plane. The range of motion of the hip joints in 3 planes is different. The maximum range of motion of the sagittal plane is 0 ° ~ 140 ° of forward flexion, 0 ° ~ 15 ° of posterior extension and 0 within 0 ° ~ 30 ° of coronary abduction. ° ~ 25 ° In the cross section, when the hip joint is flexed, the external rotation is 0 ° ~ 90 ° and the internal rotation is 0 ° ~ 70 °. When the hip joint is straightened, the rotation is smaller, and the internal and external rotation are 45 °. The hip joint flexion and extension movement is about + 40 ° ~ -5 °, and the adduction and abduction and internal and external rotation movements are about + 5 ° ~ -5 °. When going upstairs, the range of motion is large, and the range of flexion and extension is 67 °. The adduction and abduction and internal and external rotation are 28 ° and 26 °, respectively. When running, the range of flexion and extension on the sagittal plane will increase. The movement of the hip joint is mainly flexion on the sagittal plane. The normal adult acetabulum is an inverted cup-shaped deep socket in the middle of the lateral side of the hip bone, facing forward, outward, and downward, with an abduction angle of about 40 ° to 47 ° and an anteversion angle of 4 ° to 20 °. These two angles have significant biomechanical effects and are fully adapted to the kinematics of human hip joints in the sagittal plane flexion, which is essential for hip motor function. The abduction angle is the angle between the longitudinal axis of the body and the central axis of the acetabulum. When the pelvis is tilted forward 60 ° ~ 70 °, the abduction angle of the acetabulum is the largest, the acetabulum covers the femoral head the most, and the joints are the most stable. As the pelvic anteversion increases or decreases, the abduction angle decreases. The abduction angle changes greatly during human hip extension, and the abduction angle changes slightly during hip flexion. This change is compensated by the transformation of the acetabular anteversion angle during flexion. The acetabular anteversion is the angle formed by the acetabular opening and the sagittal plane, which is very important to maintain the stability of hip flexion. The shape of the anterior and posterior edges of the acetabulum has an important influence on the anteversion angle.

Studies have shown that the posterior edge of the acetabulum is linear at the proximal side and curved at the distal end, and the shape of the anterior edge of the acetabulum is also curved, straight, and irregular, making the acetabular anteversion angle larger in individuals. variation. Ziber et al. Believe that the pelvic anteversion angle gradually decreases from the posterior angle of the acetabulum to the anteversion angle. The anteversion angle of the acetabulum gradually decreases when sitting, the anteversion angle does not change much when standing, and the anteversion angle of the supine position decreases. The anteversion angle of the acetabular opening edge gradually increased from the bottom to the top, and the average increase was 0.51 ° ± 0.56 °. Moed and Maruyama's research proved that the open surface of the acetabular margin is not a plane. On the one hand, the acetabular anteversion angle can make the flexion range of the hip joint larger than that of the upright movement, and adapt to the human upright movement mode; on the other hand, it can maintain the stability of the hip joint in the state of motion. The acetabular anteversion angle gradually increases from bottom to top, so that the flexion movement of the hip joint in the sagittal plane is not blocked by the anterior edge of the acetabulum, which is conducive to increasing the flexion activity of the hip joint. Studies have shown that with the increase in hip flexion, the abduction angle of the acetabulum gradually increases, the coverage of the acetabulum on the femoral head decreases, and the hip joint tends to be unstable; if the acetabulum has no anteversion, the hip flexion reaches 90 ° The abduction angle becomes 0 ° and the coverage of the acetabular head is zero. The existence of the acetabular anteversion angle, during the hip flexion process, gradually changes the anteversion angle to the abduction angle, which maintains the effective coverage of the acetabular head to the femoral head. Therefore, physiological acetabular anteversion is very important to maintain the stability of the hip joint in flexion.

Acetabular acetabular vein and acetabular sinus

The acetabular vein is formed by the confluence of round ligament veins and hip bone veins (3 to 5 branches) in the acetabular notch. The confluent or oval-shaped enlarged sinus is often formed at the confluence. Eleven of the 28 cases had a visible sinus, accounting for 39.29%. The size of the sinus was approximately 5.0 mm x 3.0 mm. The sinus was located just outside the acetabular transverse ligament, and 4 to 6 genera branched into the sinus in fingers. There were 17 cases without sinus formation, accounting for 60.71%. The acetabular vein exits the acetabulum through the acetabular hole below the transverse ligament of the acetabulum, and merges with the venous ring of the acetabular part outside the acetabular hole, passes inward and upward through the posterior branch of the obturator vein, and is finally injected into the internal iliac vein. The veins of the acetabulum are connected inward and downward with the medial femoral circumflex and superior gluteal veins.