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View Full Version : Summary (finally!)- 3 million cycles?



Alison Mcconnell
12-18-2000, 11:37 AM
Hello!

Thank you to all who replied to my original inquiry! I really appreciate
you input :)

Here is a summary, followed by the original question:

- the consensus was that most people actually test to 5million cycles
(approx 5 years), for with current prostheses both in-vitro and clinical
wear is often not seen before that point
- after 2.5-3 million cycles, it is accepted that the amount of wear can be
extrapolated
- an excellent suggestion was that if time (and money) aren't limited,
testing to 10 million cycles would be ideal, since survivorship is ~90%
beyond 10 years.
- an interesting point was also that, for the more active patient, loading
profiles might be more important than testing duration

Thanks again for your input! (Sorry x 10^6 for my tardiness!)
:)
happy new year!
alison mcconnell



Hi there!

I'm a graduate student working on wear testing of polyethylene for use in
total joint replacements. The traditional length of testing is 3 million
cycles and 1 million cycles is accepted as representing approximately one
year of motion. Schmalzried et al (J Bone & Jt Surg, Vol 80-A, No1, Jan
98, pp54-59) reported an average of 0.9 million cycles per year for each
joint of the lower extremity (111 non-randomized volunteers), but also
report the most active patient as walking 3.5 times the average number of
steps per day.

Is 3 years a "make it or break it" point within the lifespan of a
prosthesis or why is 3 years worth of wear considered to be sufficient for
wear testing of purposes? In addition, is the average what should be
tested, or higher than average? How do we ensure success with implants for
patients who are more active than 'average'?

Thanks in advance for your replies! I'll be sure to post what I receive.

Sincerely,
Alison McConnell
Alison McConnell
M.Sc. Candidate
Dept of Mechanical Engineering, Queen's University

Human Mobility Research Centre (formerly Clinical Mechanics Group)
Queen's University
Apps Medical Research Centre
Kingston General Hospital
Kingston, Ontario
K7L 2V7
Canada

(tel) ++1 613 548-2430
(tel) ++1 613 549-6666 xt 2152 (direct)
(fax) ++1 613 549-2529

mcconn@me.queensu.ca

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