“To keep the body in good health is a duty...”~Buddha
The hip joints are responsible for bearing the weight of our bodies. When a person is standing, the weight of the upper body is divided in half where the spine meets the pelvis and distributed evenly between the two hip joints. Since each of these joints must bear one half of the body weight, we would expect them to be extremely stable, strong joints. Surprisingly, the hip joint is one of the most flexible joints in the body, second only in flexibility to the shoulder joint.
This joint is a ball and socket joint formed where the ball-shaped head of the thigh bone, or femur, fits into an indentation, or shallow socket, in the pelvis called the acetabulum. This type of joint allows for movement in almost any direction. The hip is capable of flexing, extending, abducting (moving away from the center of the body), adducting (moving toward the center of the body), or a combination of all these movements called circumduction, which allows for hip rotation.
The joint is lined with a pearly blue hyaline cartilage. This type of cartilage is strong but flexible and elastic and is found in most of the body’s joints. It allows for a free gliding motion between the femur and the acetabulum and also acts as a shock absorber, during activities like jumping, running, or walking.
The joint is also lined with synovial membranes. These membranes secrete synovial fluid, which lubricates the body’s joints, reducing friction and keeping the bones sliding freely against each other.
The femur is held in place by a capsule made up of the iliofemoral ligament, the pubofemoral ligament, and the ischiofemoral ligament. The iliofemoral ligament, which is also called the Y-ligament because of its shape, runs from the outer rim of the acetabulum to the base of the femoral neck and to the lesser trochanter (the small protrusion on the inside of the femur). The pubofemoral ligament runs across the front of the joint, and the ischiofemoral ligament runs across the back of the joint, and these both help prevent hyperextension of the hip joint. The ligamentum teres is a ligament that attaches the femur to the acetabulum.
The hip joint is surrounded by a multitude of muscles that provide strength and stability to this flexible joint. Each of these muscles perform at least two actions. Generally, the muscles that run along the front of the thigh, often referred to as the quadriceps, are responsible for flexing the hip, and the muscles that run along the back of the thigh, often called the hamstrings, are responsible for extending the hip
, and most of the muscles responsible for outwardly rotating the leg begin at the back of the hip joint and run down the outside of the leg.
My next blog post will focus on conditions and injuries of the hip that are common in dance.