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
