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Estimation, Search, and Planning (ESP) Research Group

Modifying the design of the Oxford domed lateral unicompartmental knee replacement implant reduces the risk of medial bearing dislocation

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

Background: The Oxford Domed Lateral (ODL) Unicompartmental Knee Replacement (UKR) has some advantages over other lateral UKRs, but the mobile bearing dislocation rate is high (1–6%). Medial dislocations, with the bearing lodged on the tibial component wall, are most common. Anterior/posterior dislocations are rare. For a dislocation to occur distraction of the joint is required. We have developed and validated a dislocation analysis tool based on a computer model of the ODL with a robotics path-planning algorithm to determine the Vertical Distraction required for a Dislocation (VDD), which is inversely related to the risk of dislocation.

Objectives: To modify the ODL design so the risk of medial dislocation decreases to that of an anterior/posterior dislocation.

Methods: The components were modified using Solidworks. For each modification the dislocation analysis tool was used to determine the VDD for medial dislocation (with bearing 0–6mm from the tibial wall). This was compared with the original implant to identify the modifications that were most effective at reducing the dislocation risk. These modifications were combined into a final design, which was assessed.

Results: Modifying the tibial component plateau, changing the femoral component width and making the bearing wider medially had little effect on VDD. Shifting the femoral sphere centre medially decreased VDD. Shifting the femoral sphere laterally, increasing tibial wall height and increasing bearing width laterally increased VDD. A modified implant with a femoral sphere centre 3mm lateral, wall 2.8mm higher, and bearing 2mm wider laterally, implanted so the bearing is ≤4mm from the tibial wall with a bearing thickness ≥4mm had a minimum VDD for medial dislocation of 5.75mm, which is larger than the minimum VDD for anterior/posterior dislocation of 5.5mm.

Conclusions: A modified ODL design should decrease the dislocation rate to an acceptable level, however, further testing in cadavers is required.

Publication Details
Abstract-Refereed Conference Paper
British Orthopaedic Research Society (BORS) Annual Meeting
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Podium presentation
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BibTeX Entry
author = {Irene Yang and Jonathan D Gammell and David W Murray and Stephen J Mellon},
title = {Modifying the design of the {Oxford} domed lateral unicompartmental knee replacement implant reduces the risk of medial bearing dislocation},
booktitle = {Proceedings of the British Orthopaedic Research Society ({BORS}) Annual Meeting},
year = {2021},
month = {13--14 } # sep,
doi = {10.1302/1358-992X.2021.16.020},