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Estimation, Search, and Planning (ESP) Research Group

The Oxford domed lateral unicompartmental knee replacement implant: Increasing wall height reduces the risk of bearing dislocation

Authors
  1. Irene Yang
  2. Jonathan D. Gammell
  3. David W. Murray
  4. Stephen J. Mellon
Publication Date
Abstract

Aim Due to lateral ligament laxity, bearing dislocation occurs in 1–6% of Oxford Domed Lateral replacements. Most dislocations are medial but they do rarely occur anteriorly or posteriorly. The aim was to decrease the risk of dislocation.

Method For a bearing to dislocate the femoral component has to be distracted from the tibial component. A robotic-path-planning-algorithm was used with a computer model of the implant in different configurations to determine the Vertical Distraction needed for Dislocation (VDD).

Results With current components, VDD anteriorly/posteriorly was 5.5mm to 6.5mm and medially was 3.5mm to 5.75mm. A thicker bearing increased VDD medially and decreased VDD anteriorly/posteriorly (0.1mm/1mm thickness increase). VDD medially increased with the bearing closer to the tibial wall (0.5mm/1mm closer), or by increasing the tibial wall height (1mm/1mm height increase). VDD anteriorly/posteriorly was not influenced by bearing position or wall height. To prevent collision between the femoral and tibial components an increase in wall height must be accompanied by a similar increase in minimum bearing thickness. Increasing the wall height and minimum bearing thickness by 2mm and ensuring the bearing is 4mm or less from the wall increased the minimum VDD medially to 5.5mm.

Conclusion The lower VDD medially than anteriorly/posteriorly explains why medial dislocation is more common. If the wall height is increased by 2mm, the minimum bearing thickness is 5mm and the surgeon ensured the bearing is 4mm or less from the wall the medial dislocation rate should be similar to the anterior/posterior dislocation rate, which is acceptable.

Publication Details
Type
Journal Paper
Journal
Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine
Notes
To appear
BibTeX Entry
@article{yang_joeim21,
author = {Irene Yang and Jonathan D Gammell and David W Murray and Stephen J Mellon},
title = {The {Oxford} domed lateral unicompartmental knee replacement implant: {Increasing} wall height reduces the risk of bearing dislocation},
journal = {Proceedings of the Institution of Mechanical Engineers, Part H: Journal of Engineering in Medicine},
year = {2021},
}