Over 160,000 hip replacements are carried out every year in the United Stated. The most common reason is degenerative arthritis, the gradual deterioration or wearing out of the hip joint. In this procedure the two parts of the hip joint are removed and replaced with a metallic prosthesis. The surgery is better than 90% successful allowing a person to return to normal function.

Anatomy and Function of the Hip

• The hip is a 'ball and socket' joint formed between two bones, the hipbone and the femur (Figure 1)
  
• The hipbone on each side is attached to the sacrum, the lowest bone in the spine and the three form the bones of the pelvis
  
• The hipbone forms the bony connection between the spine and leg and is formed by the fusion of three bones, the ilium, ischium and pubis.
  
• The ilium is the bone found on each side just below the belt line, the most prominent part being the crest
  
• The ischium protrudes backwards and is the bone that is sat upon
  
• The pubis is the bone found just above the genital organs
  
• The acetabulum is a half sphere shaped depression in the hipbone and formed by contributions from all of the three component bones. It is lined with smooth cartilage
  
• The femur is the long bone that extends from the hip to the knee
  
  1. The upper end consists of the head, neck, greater trochanter and lesser trochanter
     
  2. The head and neck come off the shaft of the femur at approximately 125 degrees
     
  3. The two-thirds spherical shaped head is covered with smooth cartilage. The head fits into the acetabulum to form the hip joint
     
  4. The greater trochanter is a rounded protrusion of the femur that can be felt at the upper end of the thigh about 4 inches (10 centimeters) below the crest of the ilium
     
• A fibrous joint capsule is lined with synovium, a special tissue that lines all motion joints and produces a lubricating fluid
  
• The joint capsule, muscles and ligaments hold the two bones of the joint together

Figure 1 - Anatomy of the hip joint. Note the parts of the femur (left). The hipbone is made up of three bones, the ilium, ischium and pubis (middle). The head of the femur fits into the acetabulum of the hipbone to form the hip joint covered by a capsule.