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

  • ┬áCemented 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

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