Anatomy

The hip is a ball and socket joint. It permits flexion, extension, abduction, adduction, and rotation. The upper area of the thighbone, known as the femoral head, forms the ball portion. The round area of the lower pelvis, known as the acetabulum, forms the socket portion.

The femoral head fits inside the acetabulum and both bones are covered by cartilage. Cartilage is a tough protective layer of tissue that acts as a cushion. In addition, cartilage is coated with synovial fluid, which acts as a lubricant to reduce wear during joint motion.

The prime mover of the thigh and hip flexion is the iliopsoas. The hamstring and gluteus maximus muscles control extension.

A normal hip joint has healthy cartilage that allows very smooth movement between the femoral head and acetabulum. However, a diseased hip shows degeneration of the cartilage, which leads to swelling, inflammation, and pain. In some cases, bone will begin to contact bone, which can significantly reduce function.