Hip range of motion

The hip joint is the most important part of the human skeleton. If there is a problem with the hip joint, it will easily limit the free movement of the hip joint. The hip joint is composed of ligaments, periosteum and fat. Under the action of the ligaments, the hip joint can move freely. Under normal circumstances, the gap width of an adult is about 4-5mm, and the joint can move freely in life without restriction.

Hip range of motion

The hip joint, composed of the femoral head and the acetabulum, is a ball and socket joint and a typical bar-to-acetabulum joint.

Anatomy

The femoral articular surface accounts for 2/3 of the head area and is embedded in the acetabulum. The acetabular rim surrounds the acetabular socket, which is filled with fat; the acetabular labrum is attached to the rim of the socket to increase the depth of the socket. The transverse acetabular ligament closes the acetabular notch, and the nerves and blood vessels pass under the ligament to enter and exit the joint. The gap between the acetabulum and the articular surface of the femoral head is the hip joint space, which is 4 to 5 mm wide in normal adults. The upper half of the space is narrower, showing the distance between the two opposing bony articular surfaces. The lower half is wider, showing the distance between the femoral head and the floor of the acetabulum. In the frontal view, although the lower edge of the femoral neck and the upper edge of the obturator foramen of a normal person are not connected, they together form a relatively natural arc curve, called the Shenton curve. The joint capsule is generally thick and strong, but weaker in the posterior and inferior parts; in the hip bone, it is attached to the periphery of the acetabulum and the transverse ligament; in the femur, it is attached to the intertrochanteric line in front, near the greater and lesser trochanters above and below, and about 1 cm away from the intertrochanteric ridge in the posterior part.

Hip capsule and ligaments

Figure 1 Hip joint capsule and its ligaments (A, front view B, back view)

1. Ilium 2. Joint capsule 3. Iliofemoral ligament 4. Femur 5. Ischial bursa ligament

Auxiliary structures

The joint capsule itself is reinforced by ligaments

① The iliofemoral ligament is the strongest ligament in the body. It runs obliquely downward and outward from the anterior inferior iliac spine, divides into two strands, and is attached to the intertrochanteric line.

② The pubofemoral ligament runs obliquely downward and outward from the vicinity of the superior pubic branch and transitions to the joint capsule.

③ The ischiofemoral ligament runs obliquely from the posterior part of the acetabulum (ischial body) to the posterior and superior part and transitions to the joint capsule. But the lower posterior part of the joint capsule remains a weak point.

④ The orbicularis oculi is a thickening of the circular fibers on the inner surface of the fibrous capsule that surrounds the femoral neck.

⑤ The femoral head ligament is triangular in shape, with its tip attached to the femoral head concavity and its base fused with the transverse acetabular ligament. Its function is still controversial.

The characteristic of the synovial layer of the joint capsule is that in addition to lining the fibrous capsule, it also folds back and wraps around the femoral neck where the fibrous capsule is attached, forming a support band that extends to the periphery of the articular cartilage. The support band contains blood vessels to the head and neck. The arteries that reach the joint are mainly the superior and inferior gluteal arteries, the internal and lateral femoral circumflex arteries, and branches of the obturator artery. The femoral nerve, obturator nerve, and quadratus femoris nerve all have branches entering the joint. The hip joint is capable of multi-axial movement, but because the femoral head is deeply embedded in the acetabulum and is restricted by various ligaments, its range of motion is far less than that of the shoulder joint. When the knee is in extension, the hip joint can only flex to 80 degrees; when the knee is flexed, it can reach more than 110 degrees. Extension is limited by the iliofemoral ligament to only about 30 degrees. Extension is limited by the pubofemoral ligament, iliofemoral ligament and greater trochanter; adduction is limited by the lateral part of the iliofemoral ligament; the range of motion of extension and adduction is about 45 degrees. The vertical axis of femoral rotation is the line from the femoral head to the acetabulum to the medial and lateral condyles (not the longitudinal axis of the femoral body). The total range of rotation when upright is 40 to 50 degrees.