The hip carries the weight of the upper body while allowing walking, running and climbing. Its deep socket and strong ligaments make it far more stable than the shoulder.
Ball and socket
The femoral head fits into the acetabulum of the pelvis, which is deepened by a cartilage ring called the labrum. The joint allows flexion, extension, abduction, adduction and rotation.
Ligaments and muscles
Thick ligaments in the capsule, the strongest being the iliofemoral ligament in front, limit extension and let you stand with little effort. The gluteal muscles keep the pelvis level when you stand on one leg.
Blood supply
Most of the femoral head's blood comes from small arteries that run up along the femoral neck. A displaced fracture of the neck can cut them off and cause avascular necrosis of the head.
Hip fracture
In older adults with osteoporosis, a simple fall can break the femoral neck or the area between the trochanters. The leg typically looks shortened and externally rotated.
At the bedside
An older adult who falls and cannot bear weight, with a shortened, externally rotated leg, has a hip fracture until proven otherwise. A positive Trendelenburg sign, where the pelvis drops on the opposite side during one-leg standing, points to weak hip abductors.
Related guides
Written by Making Synapses. Topic reference: OpenStax, Anatomy and Physiology 2e (no text adapted).