Arthroplasty Fixation

Non-Cemented or Porous Coated

  • Components are "press fit" precisely to bone surfaces. The tight fitting junction serves as fixation.
  • Metal surfaces attaching to bone have a roughened surface coat
  • Coating may be made of metal, ceramic, polymers or a combination of these materials
  • These materials are formed into beads, irregular particles or etchings, and applied to the prosthesis
  • Irregular surface allows for bone in-growth

Below right: Porous-coated humeral prosthesis. Note roughened surface coating below head to promote a bone in-growth.

Advantages

  • ┬áIf and when prosthesis becomes loose, there may be less bone loss due to lack of cement irritant

Disadvantages

  • Bone in-growth and thus stability, requires more time than cement fixation. This is less of an issue in the shoulder, where weight bearing activity is not required.
  • Requires faultless positioning, and is technically demanding surgery
  • Requires good underlying bone for success, so contraindicated in osteopenic patients

Indications

  • Initially used in younger patients with good bone stock, this method has been found to work well in older patients as well with few complications

Contraindications

  • Advanced age
  • Osteopenia or metabolic bone disease

Cement

  • Components fixed to bone with polymethylmethacrylate cement

Advantages

  • Allows prosthesis to fit perfectly to irregularities of bone
  • Immediate stability allows for full activity post operatively

Disadvantages

  • If and when prosthesis becomes loose, the loosened cement can grind away bone, leaving less bone stock available for revision surgery

Indications

  • Failure to achieve adequate press-fit fixation
  • Poor bone stock
  • Previous arthroplasty

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