UNICOMPARTMENTAL KNEE REPLACEMENT – DOES BEARING CONGRUENCY MATTER? A FINITE ELEMENT STUDY.

Simpson D, Pandit H, Gulati A, et al. UNICOMPARTMENTAL KNEE REPLACEMENT – DOES BEARING CONGRUENCY MATTER? A FINITE ELEMENT STUDY.. Orthop Procs. 2009;91-B(SUPP_III):414-414. doi:10.1302/0301-620X.91BSUPP_III.0910414c

Simpson, DJ, et al. “UNICOMPARTMENTAL KNEE REPLACEMENT – DOES BEARING CONGRUENCY MATTER? A FINITE ELEMENT STUDY..” Orthopaedic Proceedings, vol. 91-B, no. SUPP_III, 2009, pp. 414-414., https://doi.org/10.1302/0301-620X.91BSUPP_III.0910414c

Simpson, D., Pandit, H., Gulati, A., Gray, H., Beard, D., Price, A., Murray, D., & Gill, H. (2009). UNICOMPARTMENTAL KNEE REPLACEMENT – DOES BEARING CONGRUENCY MATTER? A FINITE ELEMENT STUDY.. Orthopaedic Proceedings, 91-B(SUPP_III), 414-414. https://doi.org/10.1302/0301-620X.91BSUPP_III.0910414c

Simpson, D., Pandit, H., Gulati, A., Gray, H., Beard, D., Price, A. et al. (2009) “UNICOMPARTMENTAL KNEE REPLACEMENT – DOES BEARING CONGRUENCY MATTER? A FINITE ELEMENT STUDY..” Orthopaedic Proceedings, 91-B(SUPP_III), pp. 414-414. Available at: https://doi.org/10.1302/0301-620X.91BSUPP_III.0910414c

Simpson, DJ, HG Pandit, A Gulati, H Gray, DJ Beard, AJ Price, DW Murray, and HS Gill. “UNICOMPARTMENTAL KNEE REPLACEMENT – DOES BEARING CONGRUENCY MATTER? A FINITE ELEMENT STUDY..” Orthopaedic Proceedings 91-B, no. SUPP_III (2009): 414-414. https://doi.org/10.1302/0301-620X.91BSUPP_III.0910414c

Simpson D, Pandit H, Gulati A, Gray H, Beard D, Price A, et al. UNICOMPARTMENTAL KNEE REPLACEMENT – DOES BEARING CONGRUENCY MATTER? A FINITE ELEMENT STUDY.. Orthop Procs. 2009 Sep 1;91-B(SUPP_III):414-414. https://doi.org/10.1302/0301-620X.91BSUPP_III.0910414c

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Abstract

Statement of purpose: The aim of this study is to evaluate different designs of unicompartmental knee replacement (UKR) by comparing the peak von Mises and contact stresses in polyethylene (PE) bearings over a step-up activity.

Summary of Methods: A validated finite element (FE) model was used in this study. Three UKR designs were modelled: a spherical femoral component with a spherical PE bearing (fully-congruent), a poly-radial femoral component with a concave PE bearing (semi-congruent), and a spherical femoral component with a flat bearing (non-congruent).

Kinematic data from in-vivo fluoroscopy measurements during a step-up activity was used to determine the relative tibial-femoral position as a function of knee flexion angle for each model. Medial and lateral force distribution was adapted from loads measured in-vivo with an instrumented implant during a step-up activity. The affect that varying the bearing thickness has on the stresses in the bearing was investigated. In addition, varus-valgus mal-alignment was investigated by rotating the femoral component through 10 degrees.

Summary of Results: Only the fully congruent bearing experienced peak von Mises and contact stresses below the PE lower fatigue limit (17MPa) for the step-up activity (fully congruent PE peak contact stress, 5MPa). The highest PE contact stresses were observed for the semi-congruent and non-congruent designs, which experienced approximately 3 times the PE lower fatigue limit. Peak PE von Mises stresses for the semi-congruent and non-congruent designs were similar, peaking at approximately 25MPa. Peak PE von Mises stresses were ameliorated with increased bearing thickness. Varus-valgus mal-alignment had little effect on the peak stresses in the three UKR designs.

Statement of Conclusions: Fully congruent articulating surfaces significantly reduce the peak contact stresses and von Mises stresses in the bearing. The FE model demonstrates that fully congruent bearings as thin as 2.5mm can be used without increasing the contact stresses significantly. Fully congruent designs can use thinner bearings and enable greater bone preservation.

Correspondence should be addressed to Mr T Wilton, c/o BOA, BASK at the Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE, England.