Basic Anatomy

• Each hip joint consists of a ball and socket that supports most of the body's weight. At the top of the thighbone is the femoral head (ball), which seats itself into the round opening (socket) of the pelvis. This structure is supported by ligaments that stabilize each leg, all encapsulated by a membrane that produces lubricants to reduce friction. The most common cause of hip discomfort is arthritis that causes a deterioration of the bones as they connect, resulting in increased friction and severe pain.
  
  

The Mechanics

• Advances in technology provide a number of options when considering methods of replacement. Hip replacement prosthetics consist of three parts: a stem, ball and cup. These vary in size in order to accommodate different body types. Since there are a number of manufacturers that make hip prosthetics, there are several variations on design. When deciding on a specific design, your doctor will take into account your age, weight, general health and level of physical activity.
  
  

Types of Material

• The most common material used for stem implants is titanium or a cobalt and chromium based alloy. Both of these are porous to allow the bone to grow into the stem for optimum strength. The ball portion of the implant is typically made up of either a cobalt chromium alloy or a ceramic composite consisting of aluminum or zirconium oxide which is polished to individual specifications for friction free rotation. The socket portion of the implant is made up of ultra-high molecular weight polyethylene, metal or a combination of the two.
  
  

Cemented Hip Replacement

• Acrylic polymer bone cement is the preferred method of stem to bone fusion for patients with poor bone density, as found in the elderly. This reduces the likelihood of fractures in the future. Cemented fusion offers faster rehabilitation with most patients able to walk the same day of surgery.
  
  

Non-Cemented Hip Replacement

• This type of stem-to-bone fusion is usually restricted to younger patients with good bone density and those with active lifestyles. It requires more recovery time to allow the bone to grow into the stem to form a permanent fusion. While opinions vary as to which method is better, some surgeons use non-cemented hip replacement exclusively.
  
  

Advanced Procedures

• Techniques used for hip-replacement surgery continue to evolve. This includes minimally invasive procedures requiring less recovery time with a reduced chance of infection. Additional advances include short-stem prosthetics and hip resurfacing as a potential option to complete hip replacement. For more information on the advances in hip replacement technology, visit the Mayo Clinic website at www.mayoclinic.org.