Cookies on this website

We use cookies to ensure that we give you the best experience on our website. If you click 'Accept all cookies' we'll assume that you are happy to receive all cookies and you won't see this message again. If you click 'Reject all non-essential cookies' only necessary cookies providing core functionality such as security, network management, and accessibility will be enabled. Click 'Find out more' for information on how to change your cookie settings.

BACKGROUND: Unicompartmental knee replacement offers an effective treatment for patients with single compartment knee disease and is becoming an increasingly popular alternative to total knee replacement. An important cause of failure in a unicompartmental knee replacement implant is polyethylene wear. Significant contributory factors to the amount of polyethylene wear are contact stress, bearing alignment, congruency and thickness. METHODS: Four different unicompartmental knee replacement implant designs (Fully-Congruent; Partially-Congruent; Non-Congruent-metal-backed; Non-Congruent-all-polyethylene) were inserted into a validated finite element model of a proximal tibia. The effect that bearing congruency, alignment and thickness had on the polyethylene stresses during a simulated step-up activity for each design was investigated. Additionally, contact pressures were compared to those calculated from Hertz elastic theory. FINDINGS: Only the Fully-Congruent bearing experienced peak von Mises and contact stresses below the lower fatigue limit for polyethylene during the step-up activity. The highest polyethylene contact stresses were observed for the Partially-Congruent and Non-Congruent-metal-backed designs, which experienced approximately three times the polyethylene lower fatigue limit. Increasing the bearing thickness from 3.5mm to 8.5mm of the Non-Congruent design decreased the contact stresses in the bearing; however they did not fall below the lower fatigue limit for polyethylene. Good agreement between finite element and Hertz contact pressures was found. INTERPRETATION: Fully congruent unicompartmental knee replacement bearings can be markedly thinner without approaching the material failure limit, have a greater potential to preserve bone stock and are less likely to fail mechanically.

Original publication

DOI

10.1016/j.clinbiomech.2008.06.001

Type

Journal article

Journal

Clin biomech (bristol, avon)

Publication Date

11/2008

Volume

23

Pages

1148 - 1157

Keywords

Arthroplasty, Replacement, Knee, Computer Simulation, Elastic Modulus, Hip Prosthesis, Humans, Knee Joint, Models, Biological, Stress, Mechanical, Tibia