The Hip Joint: A Ball-and-Socket Design

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The hip is one of the body’s largest and strongest joints. It connects the thigh bone (femur) to the pelvis. The rounded head of the femur fits into the acetabulum, a socket in the pelvic bone. This design allows for a wide range of motion, including walking, running, bending, and sitting.

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Bones of the Hip

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• Femur (thigh bone): The upper part of the femur forms the “ball” of the joint.

• Pelvis: The acetabulum forms the “socket,” providing stability and support.

• Sacrum and spine connection: The hip links to the lower spine through the pelvis, playing a key role in balance and posture.

Function: These bones bear weight, absorb forces from movement, and protect nearby organs.

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Cartilage

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A layer of smooth cartilage covers the ball and socket surfaces, allowing the bones to glide without friction. Cartilage also acts as a shock absorber during walking, running, or climbing stairs.

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Labrum

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The acetabular labrum is a ring of cartilage that deepens the hip socket. It stabilizes the joint and helps keep the femoral head securely in place. Tears in the labrum are a common source of hip pain.

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Muscles and Tendons

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The hip is surrounded by strong muscles and tendons that provide strength and mobility:

• Gluteal muscles (buttocks): Power hip extension and stability.

• Hip flexors: Help lift the leg when walking or climbing.

• Adductors: Pull the leg inward for balance.

• Abductors: Move the leg outward and stabilize the pelvis during walking.

Function: Together, these muscles and tendons control motion, absorb stress, and maintain balance.

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Ligaments

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Thick bands of tissue connect the bones and keep the hip joint stable. The main ligaments prevent the hip from dislocating while allowing natural movement.

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Bursae

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Small fluid-filled sacs called bursae reduce friction between muscles, tendons, and bones. When inflamed, they can cause a condition known as bursitis, a common cause of hip pain.

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Why Hip Anatomy Matters

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Understanding your hip’s anatomy can make it easier to recognize when something is wrong. Pain, stiffness, or loss of motion often indicate problems with cartilage, labrum, muscles, or tendons. At the Puerto Rico Hip Institute, we use advanced imaging and evidence-based care to identify the exact source of hip pain and create the right treatment plan.