Total hip replacement

Joint prosthesis
- They are used to replace damaged joints
Total hip replacement (THR)
- Surgical technique
  - The acetabulum is opened and reamed (hollowed out)
    - This removes any residual cartilage and leaves only the bony surface
  - The neck of the femur is cut with a saw
  - The medullary cavity is reamed to make space for the femoral stem
  - If bone cement is used, bone cement is applied to the medullary cavity of the femur and the acetabulum to fix the femoral stem and the acetabular parts, respectively
  - If bone cement is not used the femoral stem and acetabular parts are banged in
- Components
  - Acetabular component
    - Polyethylene insert or liner
      - A special kind of plastic
      - Provides the mobile part of the joint
    - Acetabular shell
      - Made of metal
  - Femoral head
  - Femoral stem – goes into medullary canal of femur
- Types
  - Cemented THR
    - Both femoral component and acetabular component are fixed to the bone with bone cement
    - Bone cement dries after 15 minutes, meaning that the prosthesis can (in theory) be walked on and used immediately after the procedure
      - However, no patient can walk immediately after any major surgery
    - Bone cement is created by mixing a powder with a solution -> then applied with a cement gun
    - The bone cement will enter the lacunae of the bone, fixing the prosthesis to the bone
  - Uncemented THR
    - Does not use bone cement – instead, the prosthesis is fixed by force
      - This is called “press fit”
    - The acetabular part is banged into the acetabulum
    - The femoral stem is banged into the medullary cavity of the femur
    - The prosthesis has a porous coating and the bony part is rough, which creates a lot of friction between the prosthesis and the bone
      - This is called primary fixation
      - If the friction itself is not enough the prosthesis can be further fixed with screws
    - After some weeks the bone will grow into the porous surface of the prosthesis
      - This is called secondary or final fixation
      - This takes time, and the patient must not be weightbearing during this time
- Indications
  - Cemented THR
    - For elderly
    - For less active patients
    - For those with poor bone quality
  - Uncemented THR
    - For young, active patients
    - For those with good bone quality