Bearing Surfaces

The goal of hip replacement surgery is to help regain natural hip function. Hip replacement surgery involves replacement of the damaged hip joint with an implant. Hip joint resembles a ball and socket joint where acetabular cup forms socket and head of femur bone rotates within the acetabular cup.  During hip replacement surgery worn out acetabular component, femur head, or both may be replaced and these implants may be made up of different materials.

The implant comprises of acetabular cup and femoral head. Acetabular cup contains a shell and a liner. The ball, replacement for femoral head, will be attached to the stem. This ball attached to stem will then be placed into the socket and this forms the artificial hip joint. The site at which the movable parts of new hip joint unite to form a movable joint is called as ‘bearing’.

Hip Bearing Surfaces

Bearing is made of different materials and selection of the type of material (bearing surface) is very important. Different materials used for these implants are metal, ceramic, and polyethylene. Combination of these materials may also be used. Each of these bearing surfaces has their unique advantages and disadvantages. Therefore your surgeon decides on which bearing surface would be best for you. Your surgeon considers various factors such as your age, standard of living and body weight for selecting the bearing surface. One or more than one type of bearing may be used by your surgeon depending upon the durability, level of performance, wear resistance, and your personal needs.

Cross-linked polyethylene

Cross-linked polyethylene is usually used for lining the acetabular cup. The acetabular cup and the ball will be made up of stainless steel, cast or wrought cobalt, or metal-alloy.
Advantages

  • Better durability
  • non-toxic
  • proven long-term success results
  • Better toughness that suits people of different lifestyles

Disadvantages
Wear out over time causing inflammation and bone loss necessitating revision surgery.

Metal

Metal on metal bearings was commonly used earlier and advent of polyethylene surfaces replaced the metal-on-metal surfaces. However with increase in demand for better designs, stronger and long lasting surfaces metal-on-metal bearings regained their importance. In metal on metal implants the acetabular cup, lining and femoral head will be made of metals.
Advantages

  • Larger femoral heads can be used and offer the convenience of greater range -of-motion
  • Greater stability and minimal risk of dislocation
  • Minimal risk of inflammation and loosening of implant
  • Durability and release of particles into the body are better compared to polyethylene surfaces

Disadvantage

  • Not suitable for those with metal sensitivity

Ceramic

These bearings are available in two forms, a ceramic femoral head with a polyethylene liner, or a ceramic femoral head with a ceramic liner.
Advantages

  • Better lubrication and minimal friction
  • Better performance compared to polyethylene and metal-on-metal bearings

Disadvantages

  • Risk of fracture
  • Ceramic implants are hard and brittle, it can crack
  • Loss of more bone tissue because of size limitations
  • Costlier compared to other bearing surfaces

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