How long does a knee replacement last?

There is a lot of misinformation about the longevity of a knee replacement. Patients are understandably apprehensive to have a procedure that may not last, especially if they are younger. However, registry data shows very good survival of total knee replacements at 10+ years.

The Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR) is an initiative of the Australian Orthopaedic Association (AOA), and funded by the Commonwealth Department of Health. It began in 1999, and aims to record every knee replacement, the prosthesis used, and the reason for the operation. If that patient’s operation has to be revised (re-done), this is also recorded, along with the reason for failure. This occurs even if the patient has their second surgery with another surgeon or in another area.

The AOANJRR provides excellent information regarding the longevity of total knee replacements, unicompartmental knee replacements, and specific information about each brand and design.

Total knee replacement (TKR)

Cumulative Percent Revision of Primary Total Knee Replacement for Osteoarthritis (adapted from AOANJRR Annual Report 2015)

ProsthesisNumber recorded1 yr3yrs5yrs7yrs10yrs14 yrs
All total knee replacements4328331.02.83.74.45.57.2

So, in over 430 000 total knee replacements in Australia logged since 1999, only 5.5% have been re-done after 10 years.

Unicompartmental knee replacement (UKR)

Cumulative Percent Revision of Primary Total Knee Replacement for Osteoarthritis (adapted from AOANJRR Annual Report 2015)

ProsthesisNumber recorded1 yr3yrs5yrs7yrs10yrs14 yrs
All uni-knee replacements430872.25.88.310.715.020.5
My current prosthesis44841.43.74.85.68.1*

* no results available yet due to age of prosthesis.

Uni-knee, UKR, or half-knee replacement, have traditionally had a higher rate of failure. However, with better understanding of how to position the implant, better component design, and better patient selection, the newest generation of UKR’s has been performing at a similar level to TKR.

What are the factors that can affect the longevity of a knee replacement?

  • Implant alignment
    • Many studies correlate the position of the implant and the overall alignment and ligament balance of the knee as a very important factor in both function and survival of the implant. This is determined by the surgeon, and is critical to the outcome. Surgeons can use tools such as computer navigation or planning to ensure the best possible alignment.
  • Age of the patient
    • Younger patients have a higher failure rate than older patients. This may be for several reasons:
      • Increased activity levels and increased stress on the prosthesis
      • Older patients may tolerate a failing knee and avoid re-do.
      • Older patients may pass away sooner after their TKR than younger patients
      • Patient activity level
  • Theoretically, activity may promote wear of the plastic bearing, or loosening of the bond between prosthesis and bone. However, with newer more durable plastics, and good implant alignment, this is becoming less of a concern.
  • Implant design
    • Modern implants allow better soft tissue balance and motion, and limit stresses at the interfaces. However, some implants have a higher than anticipated failure rate. The joint registry has been fantastic at identifying problematic implants early and flagging them to surgeons.
  • Plastic bearing quality
    • Better understanding of how to process and store the polyethylene bearing surface has improved longevity. Cross linking of the polyethylene using radiation has reduced wear rates, and the addition of materials such as vitamin E to the plastic is thought to scavenge damaging free radicals.

To further discuss which option is right for you, contact me on 1300 695 633 or enquiries@drbalalla.com.au

Copyright Dr Bu Balalla 2016

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