Hip Anatomy and Terminology

The hip is the largest “ball-and-socket” joint in the body. It is held together by ligaments, tendons, and a joint capsule.

The ball is called the “femoral [fem-er-uhl] head,” which is the top of the femur or thigh bone.

The socket is called the “acetabulum” [as-i-tab-yuh-luhm] and is a part of the pelvis.

The femoral head fits into the acetabulum forming the hip joint. They fit together so the ball can rotate freely in the socket.

Articular cartilage is a very smooth surface that covers the femoral head and the acetabulum so that the hip joint glides easily during motion.

The labrum is a soft rim that lines the edge of the acetabulum. The labrum creates a seal of the hip joint. This seal helps keep an oily fluid called synovial fluid inside the hip joint. The labrum also helps stabilize the hip. The hip is also stabilized by the surrounding muscles, ligaments, tendons and joint capsule.

Doctors use a number of different terms for hip dysplasia depending on severity and time of occurrence. These names include:

  • Hip Dysplasia
  • Developmental Dislocation of the Hip (DDH)
  • Hip Dislocation
  • Developmental Dysplasia of the Hip (DDH)
  • Acetabular Dysplasia
  • Congenital Dislocation of the Hip (CDH)

Abductor muscles lift the leg to the side and keep the pelvis level when walking. If the hip socket is shallow, then these muscles must work harder

Psoas muscle also called the Iliopsoas muscle. This is a flexor of the hip and must work harder when the hip socket is shallow. The section that runs across the front of the pelvis and hip joint may cause a snapping feeling or noise as the hip moves underneath this muscle.   

Adductor muscles are the inner thigh muscles that bring the thighs together. These are rarely painful in people with hip dysplasia.

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