Fixation
Cement
- Most common approach to fixation, accounting for 90% of cases
- Components fixed to bone with polymethylmethacrylate cement
- Advantages
- Allows prosthesis to fit perfectly to irregularities of bone
- Immediate stability allows for full weight bearing activities post operatively
- Reliable fixation with pain free outcomes for at least 10 years in 90 to 95% of patients1, 2
- Disadvantages
- If and when prosthesis becomes loose, the loosened cement can grind away bone, leaving less bone stock available for revision surgery
Non-Cemented or Porous Coated
On the right: Porous coated tibial prosthesis removed from patient with infection. Roughened surface coating as well as areas of bone ingrowth.
- Metal surfaces attaching to bone have a roughened surface coat
- Coating may be made of metal, ceramic, polymers or a combination of these materials
- There materials are formed into beads, irregular particles or etchings and applied to the prosthesis
- Irregular surface allows for bone ingrowth
- Components are "press fit" precisely to bone surfaces cut with jigs
- Relatively new procedure, so long-term outcomes not yet available, although Duffy et al3 reported higher revision rates with non-cemented vs. cemented fixation
- Advantages
- If and when prosthesis becomes loose, there may be less bone loss due to lack of cement irritant
- Disadvantages
- Bone ingrowth and thus stability requires time, therefore patients are limited to toe touch weight-bearing activities until at least 5 weeks after surgery
- Requires faultless positioning and is technically demanding surgery
- Requires good underlying bone for success, so contraindicated in osteopenic patients
- Indications
- Physiologically young patients
- Ideal body weight
- Cooperative and willing to restrict activities after surgery
- Good quality and quantity of bone stock
- Contraindications
- Advanced age
- Ostepenia or metabolic bone disease
- Unwilling or unable to restrict weight bearing after surgery
Hybrid
- Cemented tibial component, non-cemented femoral component
- Tibial component fixation more problematic in non-cemented surgeries with degree and extent of bone ingrowth more variable and unpredictable, leading to development of hybrid technique.
- Since isolated femoral component loosening in cemented total knees is uncommon cause of revision arthroplasty, hybrid approach may have no added benefit.
Other
- Components anchored by screws: used in conjunction with non-cemented components to aid in fixation
- Long-stemmed components: usually used for revision arthroplasty due to bone loss about the joint
