The British Journal of Rheumatology, Vol 36, 20-26, Copyright © 1997 by British Society for Rheumatology
RM Hall, A Unsworth, BM Wroblewski, P Siney and NJ Powell
Charnley prostheses, retrieved at revision surgery, were studied to assess
the effects of friction on the total hip replacement procedure. Frictional
resistance was measured using the Durham hip function simulator under both
dry and lubricated conditions. The friction factor values (f) for the
explanted prostheses were found to have a non- Gaussian distribution with
medians of 0.13 [inter-quartile range (IQR) 0.10-0.16] and 0.06 (IQR
0.005-0.08) for dry and lubricated (n = 0.01 Pa s) regimes, respectively.
New Charnley prostheses had values of f equal to 0.11 +/- 0.025 and 0.04
+/- 0.01 under the same conditions, and showed no large deviation from a
Gaussian distribution. There was found to be a statistically significant
difference in the medians of the friction factors for new and retrieved
prostheses in the lubricated regime. Ingression of cement into the worn
region of the cup was found to increase the friction factor significantly
under dry conditions. There was no evidence of an increase in the friction
factor or torque for those joints that had a loose socket with respect to
those that were fixed at revision. A decrease in the frictional torque
against number of cycles undergone by the joint in vivo may indicate that a
fatigue-type process may have a role in the loosening of the socket.
However, this relationship was found not to be significant for friction
measured under lubricated conditions and it seems unlikely that the
frictional torque generated in this type of prosthesis will contribute
significantly to the long-term loosening of the socket.
ORIGINAL PAPERS
The friction of explanted hip prostheses
Centre for Biomedical Engineering, University of Durham.
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