Hip Joint Anatomy and Its Role in Movement

In anatomy, the hip is defined as the joint between the pelvis and thighbone (femur) and the area adjacent to this particular joint. To describe the hip joint, we can say that it has a structure of a ball-and-socket joint, where the round head of the femur rests in a cavity (also called the acetabulum), which allows free rotation of the limb. Various organisms contain different sized hip in body parts.

Hip - In Animals

Reptiles and amphibians contain relatively weak pelvic girdles, and the femur gets extend horizontally. This prevents the animals from effectively resisting gravity, and their trunks often rest partially on the ground. Whereas, in mammals, the hip joint allows the femur to drop vertically, hence permitting the animal to hold itself off the ground and leading to the specializations for leaping and running.

Hip Joint

Scientifically, the hip joint is known as the acetabulofemoral joint (art. coxae), which is the joint between the acetabulum and femur of the pelvis and its main function is to support the body weight in both dynamic (for example, running and walking) and static (for example, standing) postures. The hip joints contain very crucial roles in balance retaining and maintaining the angle of pelvic inclination.

The pain of the hip could be the result of numerous causes, including osteoarthritic, nervous, traumatic, infectious, and genetic.

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Structure

Region

The greater trochanter is frequently the only palpable bony structure in the hip region since the proximal femur is more heavily protected by muscles.

Articulation

To describe, the hip joint is a synovial joint formed by the rounded head of the cup-like acetabulum and the femur of the pelvis articulating together. It also forms the primary connection between the lower limb and the bones and the axial skeleton of the pelvis and trunk. Both the joint surfaces are covered with a strong but lubricated layer, which is known as hyaline articular cartilage.

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The above hip diagram represents a healthy human hip joint radiograph.

Articular Angles of Hip

• The transverse angle of the acetabular inlet (which is also called Sharp's angle and it is generally the angle called acetabular angle without further specification) is described by measuring the angle between a line passing from the superior to the horizontal plane and inferior acetabular rim; an angle that normally measures 51° in infants and 40° in adults that affects the lateral acetabular coverage of the femoral head and many other parameters.

• Wiberg's centre-edge angle (which is called CE angle) is defined as an angle between a line from the centre of the femoral head and the vertical line to the most lateral part of the acetabulum, which can be seen on an anteroposterior radiograph.

• The sagittal angle of the acetabular inlet is described as an angle between a line that passes from the anterior to the sagittal plane and the posterior acetabular rim. in adults; it also measures 7° at birth and increases to 17°.

Femoral Neck Angle

The angle which lies between the longitudinal axes of the shaft and femoral neck is called the caput-collum-diaphyseal angle or simply CCD angle, generally measures nearly 150° in newborn and as 126° in adults (which is called as coxa norma).

An abnormally large angle is called coxa valga and an abnormally small angle, as coxa vara. Since changes in femur shape affect the knee, coxa valga is often associated with genu varum (also known as bow-leggedness), while coxa vara causes genu valgum (knock-knees).

Capsule

The capsule usually attaches to the hip bone that is outside the acetabular hip, which therefore projects into capsular space. Whereas, on the femoral side, the distance between the cartilaginous rim head and the capsular attachment at the neck's base is constant that leaves a wider extracapsular neck part at the back than at the front.

The strong but loose fibrous capsule present on the hip joint permits the hip joint to contain the second-largest range of movement (which is second, only to the shoulder) and yet supports the weight of the arms, body, and head.

Ligaments

The hip joint is the one, which is reinforced by four ligaments, where three are extracapsular and one is intracapsular.

The extracapsular ligaments are given as the ischiofemoral, iliofemoral, and pubofemoral ligaments that are attached to the pelvis bones (the ischium, ilium, and pubis, respectively). All these three strengthen the capsule and prevents an excessive range of joint movement. The iliofemoral ligament, which is twisted and Y-shaped, is the strongest ligament in the human body or the hip in the human body. It also stops the trunk from dropping backwards in the upright position without the need for muscular action. In the sitting position, it becomes relaxed, allowing the pelvis to tilt backwards into the sitting position.

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Blood Supply

The lateral circumflex femoral arteries and the medial circumflex femoral arteries, which are both generally branches of the deep artery of the thigh (also known as profunda femoris), supply blood to the hip joint. However, there are a number of variations, and either one or both can also arise directly from the femoral artery.