Hip (anatomy)

For other uses of the term, see hip (disambiguation).

In anatomy, the hip is the bony projection of the femur, known as the greater trochanter, and the overlying muscle and fat. The hip joint is the joint between the femur and the acetabulum of the pelvis and its primary function is to support the weight of the body in both static (e.g. standing) and dynamic (e.g. walking or running) postures.

Movements

Six different kinds of movements are possible in the hip joint:

Flexion and extension
Abduction and adduction
Internal (medial) and external (lateral) rotation

A synovial joint that can produce movement in more than one axis is called a multiaxial joint.

Anatomy of the hip joint

Articulation

The hip joint is a multiaxial ball and socket synovial joint formed by the articulation of the rounded head of the femur and the cuplike acetabulum of the pelvis. It forms the primary connection between the bones of the lower limb and the axial skeleton of the trunk and pelvis. Both joint surfaces are covered with a strong but lubricated layer called articular hyaline cartilage. The cuplike acetabulum forms at the union of three pelvic bones and the joint may not be fully ossified (the process of forming bone) under the age of 25 years. The depth of the acetabulum is increased by a fibrocartilaginous rim called a labrum that grips the head of the femur and secures it in the joint.

The large head of the femur is completely covered in hyaline cartilage except for a small area called the fovea or pit. This is the site of attachment for an intracapsular ligament that attaches directly from the head of the femur to the acetalum. The head of the femur is attached to the femur by a thin neck region that is often prone to fracture in the elderly, mainly due to the degenerative effects of osteoporosis.

Capsule

The strong but loose fibrous capsule of the hip joint permits the hip joint to have the second largest range of movement (second only to the shoulder) and yet support the weight of the body, arms and head. As the line of gravity falls posterior to the axis of the hip joint, the combined weight of the body seeks to extend the hip joint in normal standing and make the trunk fall backwards to the ground. To resist the stretching action on the anterior joint capsule in normal upright posture, the hip has developed two very strong anterior ligaments.

Ligaments

The hip joint is reinforced by three main ligaments.

At the front of the joint, the strong iliofemoral ligament attaches from the pelvis to femur. This Y-shaped ligament is also known as the ligament of Bigelow. This ligament seeks to resist excessive extension of the hip joint. It is often considered to be the strongest ligament in the human body.
The pubofemoral ligament attaches across the front of the joint from the pubis bone of the pelvis to the femur. This ligament is oriented more inferiorly than the iliofemoral ligament and reinforces the inferior part of the hip joint capsule. It also blends with the medial parts of the iliofemoral ligamemt.
The posterior of the hip joint capsule is reinforced by the ischiofemoral ligament that attaches from the ischial part of the acetabular rim to the femur.

There is also a small ligament called ligamentum teres or the ligament of the head of the femur. This structure is not that important as a ligament but can often be vitally important as a conduit of a small artery to the head of the femur. This arterial branch is not present in everyone but can become the only blood supply to the bone in the head of the femur when the neck of the femur is fractured or disrupted by injury in childhood.

Blood supply and nerve supply of the hip joint

The hip joint is supplied with blood from the medial circumflex femoral and lateral circumflex femoral arteries, which are both usually branches of the deep artery of the thigh (profunda femoris), but may also arise directly from the femoral artery. There is also a small contribution from a small artery in the ligament of the head of the femur which is a branch of the posterior division of the obturator artery, which becomes important to avoid avascular necrosis of the head of the femur when the blood supply from the medial and lateral circumflex arteries are disrupted (e.g. through fracture of the neck of the femur along their course).

The hip joint is supplied by a number of nerves (proprioception, nociception, etc...) including the femoral nerve, the obturator nerve, superior gluteal nerve, and the nerve to quadratus femoris.

Muscles producing movements at the hip joint

The muscles that cause movement in the hip can be divided into four groups according to their orientation around the hip joint: the gluteal group, the lateral rotator group, the adductor group, and the iliopsoas group. These muscles produce flexion, extension, lateral rotation, medial rotation, abduction, and adduction. Many of the hip muscles are responsible for more than one type of movement in the hip, as different areas of the muscle act on tendons in different ways.

Cultural Significance of Hips

It should also be noted that hips, particularly those of women, have long been associated with both fertility and general expression of sexuality. Since broad hips facilitate child birth and also serve as an anatomical queue of sexual maturity, they have been seen as an attractive trait for women for thousands of years. Many of the classical poses women take when sculpted, painted or photographed often serve to emphasize the prominence of their hips. Similarly, women's fashion through the ages has often drawn attention to the girth of the wearer's hips.

American standards of beauty for the last few decades have tended to favor women with more narrow hips. Sociological reasons for this counter-intuitive shift in aesthetics have ranged from general cultural stigma against anything resembling obesity, to a feminist theory that patriarchal institutions present narrow-hipped women as an ideal due to their closer resemblence to pre-pubescent girls.

External links

Skeletal system | Lower limb anatomy

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