Hip and Pelvis Anatomy: How Does the Hip Joint Actually Work?

Understanding your hip anatomy helps you make sense of pain, stiffness or clicking, and why a problem in one area often causes symptoms somewhere else. This page explains each part of the hip joint and pelvis in plain language, and why standing imaging matters for an accurate picture.

What bones make up the hip joint and pelvis?

The hip joint is formed where two bones meet: the femur (thigh bone) and the pelvis. The rounded top of the femur, called the femoral head, fits into a deep cup in the pelvis called the acetabulum. This ball and socket design gives the hip both strength and flexibility.

The pelvis itself is made of three bones that fuse together during adolescence:

• Ilium – the large, wing-shaped bone you feel at your waist.
• Ischium – the lower part you sit on.
• Pubis – the front section, where left and right sides meet at the pubic symphysis.

At the back, the pelvis connects to the base of the spine through the sacroiliac (SI) joints. These joints transfer load between your upper body and your legs. When the SI joint is not working properly, it can cause pain that feels like it is coming from the hip or lower back. You can learn more about SI joint dysfunction and how it relates to hip and back pain.

The angle at which the femoral head sits in the socket also matters. If the ball points too far forward or too far back, it changes how the joint moves and where stress falls. This is known as hip anteversion and retroversion, and it can only be measured accurately with the right imaging.

What do the labrum and ligaments do in the hip?

The labrum is a ring of tough, flexible cartilage that lines the rim of the acetabulum. It deepens the socket, helps seal the joint fluid inside, and improves the grip between ball and socket. A damaged labrum, known as a hip labral tear, can cause clicking, catching or a deep ache in the groin.

The hip capsule is a tough, fibrous sleeve that wraps around the entire joint. It is reinforced by three main hip ligaments. The strongest, the iliofemoral ligament, runs across the front of the hip and stops you from tipping backwards when you stand upright. These ligaments are under real tension only when you are weight-bearing, which is one reason standing imaging gives a more accurate picture than lying down.

Which hip muscles control movement and stability?

More than twenty muscles cross the hip joint. They work in groups to move and stabilise the joint during every step, squat and turn. Here are the key players.

These hip muscles do not work in isolation. They form part of a connected chain that runs from your feet up through your pelvis and spine. A tight iliopsoas, for example, can tilt the pelvis, change the curve of the lower back, and put extra load on the opposite knee. This is why pain often shows up in a different place from its true cause.

What range of movement does the hip joint allow?

The ball and socket design of the hip allows movement in all directions: forward (flexion), backward (extension), out to the side (abduction), across the body (adduction) and rotation inward and outward. This wide range of movement is what lets you walk, run, sit cross-legged and climb stairs.

The trade-off for this freedom is complexity. Because so many structures work together, a small change in one part, such as the angle of the femoral head, the depth of the socket, or the tension of a single ligament, can alter how load is transferred through the entire pelvis. Over time, the body compensates. You may not feel it in the hip at all. Instead, the first symptom might be a sore lower back, a stiff SI joint, or a niggling knee.

Why does standing imaging show hip problems that lying-down scans miss?

When you lie down for a standard X-ray, CT or MRI, gravity is taken out of the equation. Your muscles relax, your pelvis settles into a neutral position, and alignment problems can disappear. This is why a scan may come back "normal" even when you are in pain every time you stand or walk.

ScanAlign standing EOS imaging uses about 90% less radiation than a standard X-ray, around ten times less. A single scan captures your full skeleton from head to toe while you stand naturally, giving a complete picture of how your bones and joints relate to each other under load.

Frequently asked questions about hip and pelvis anatomy