The influence of femoral condylar lift-off on the wear of artificial knee joints.
In vivo fluoroscopic studies of patients with total knee replacements (TKRs) have shown lift-off of the femoral condyles from the tibial insert. This study investigated the influence of femoral condylar lift-off on the ultra-high molecular weight polyethylene (UHMWPE) wear of fixed bearing (FB) and rotating platform mobile bearing (RP MB) total knee replacements, using a physiological knee joint simulator. In the absence of lift-off, the RP MB knees exhibited a lower wear rate of 5.2 +/- 2.2 mm3 per million cycles (mm3/MC) compared with 8.8 +/- 4.8 mm3/MC for the FB knees. The presence of femoral condylar lift-off was found to accelerate the wear of the FB and RP MB knees tested in this study to 16.4 +/- 2.9 and 16.9 +/- 2.9 mm3/MC respectively. For the RP MB knees the increase in wear rate was more marked, resulting in a similar wear rate for both designs of knee under lift-off conditions. In both cases the medial condyle displayed more wear damage. This study has shown that a small amount of abduction/adduction lift-off and medial-lateral shift increases wear and that the increase in wear is design dependent. In this simulator test, lift-off was simulated on every cycle, whereas the amount of wear and effect of lift-off clinically would depend on the frequency of occurrence of lift-off in vivo.
Jennings
L M
LM
Institute of Medical and Biological Engineering, School of Mechanical Engineering, University of Leeds, Leeds, UK. l.m.jennings@leeds.ac.uk
Bell
C I
CI
Ingham
E
E
Komistek
R D
RD
Stone
M H
MH
Fisher
J
J
D019544:Equipment Failure Analysis; D005269:Femur / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007593:Joint Instability / Q000209:etiology / Q000503:physiopathology*; D007720:Knee Prosthesis / Q000009:adverse effects*; D009068:Movement; D011475:Prosthesis Failure; D016474:Weight-Bearing