Joints - Hip Arthroplasty Flashcards
Common reason for joint replacement? (4)
Rheumatoid Arthritis
Gout
Injury/Post-trauma
Osteoarthritis
Requirements for a joint implant? (5)
Biocompatible Wear-resistant Load bearing Revise-able Reliable (insensitive to alignment, size mismatch)
What MUST joint implants do?
Restore function
Relieve pain
What 3 classes of materials are used
Metals
Ceramics
Polymers
What kinds of metals are used?
Alloys
Example of metals used?
Titanium alloys (lightest)
Cobalt-Chromium alloys
Stainless steel
Example of ceramic materials used?
Alumina
Zirconia
Bioactive glass
Good features of Alumina
High Youngs modulus (stiff)
Finished to a high polish (low friction)
Great wear & corrosion resistance
Examples of Polymers used?
Ultra-High Molecular Weight Polyethylene (UHMWPE)
Polymethylmethacrylate (PMMA)
What is a common use for PMMA ?
Bone cement
What is an issue with metal-on-metal implants?
Metallosis - an immune reaction when toxic metal debris shed off the surface and enter bloodstream
What is the function of bone cement? (3)
Facilitates fixation between the implant and bone
Allows even transfer of load from the implant to the bone
Shock absorber
Indications for bone cement
Osteoporotic bone
Repeatedly Irradiated bone
Indication for uncemented implant
Young, healthy individuals
Issue with ceramic on ceramic implants
Makes noise
Expensive
Requires expert insertion
Advantages of bone cement? (2)
Quick recovery as cement dries quickly
Antibiotics can be added
Disadvantages of bone cement? (2)
Cement can break down and lead to debris which can:
Cause inflammation
Embolise to the lungs
How do implants fail?
Fracture
Stress shielding
What is stress shielding
- Stress shielding refers to the reduction in bone density (osteopenia) as a result of relief of typical stress from the bone by an implant
- Leads to loosening
Issues with metal-polyethylene implants (4)
Aseptic loosening
Adhesive wear
Abrasive wear
Fatigue wear
Explain aseptic loosening
Loosening of an implant without infection
Causes of aseptic loosening
Inadequate initial fixation
Mechanical loss of fixation over time (eg cement breakdown)
Biological loss of fixation (Particulate debris leads to pseudosynovial fluid between implant and bone which causes cytokines to stimulate osteolysis)
Explain adhesive wear
Small portions of UHMWPE surface adhere to the opposing metal or ceramic bearing surface
May change the surface topography of the metal component
Explain abrasive wear
When 2 surfaces slide across each other the harder scrapes the softer one
causes debris to be released
Explain fatigue wear
Repeated loading between 2 surfaces lead to cracks forming
Debris can be released
