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
- If 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
