Posterior Bearing Overhang Following Medial and Lateral Mobile Bearing Unicompartmental Knee Replacements

A prospective Cohort Study. Level 2 evidence

Benjamin Martin, Elise Pegg, Bernard Van Duren, Hassan Mohammad, Hemant Pandit, Stephen J Mellon, David Murray

Research output: Contribution to journalArticle

Abstract

This study explores the extent of bearing overhang following mobile bearing Oxford unicompartmental knee replacement. The Oxford components are designed to be fully congruent, however knee movements involve femoral rollback, which may result in bearing overhang at the posterior margin of the tibial implant, with potential implications for; pain, wear, and dislocation.

Movement is known to be greater, and therefore posterior overhang more likely to occur, with; lateral compared to medial implants, anterior cruciate ligament deficiency, and at extremes of movement.

32 knees with medial, and 20 with domed lateral, unicompartmental knee implants (Oxford Phase III, Zimmer Biomet) had sagittal plane knee fluoroscopy during step-up and forward lunge exercises. Within the 32 medial implants, 16 were ACL deficient, and 16 ACL intact. The bearing position was inferred from the relative position of the femoral and tibial components. Based on the individual component sizes and geometry the extent the posterior part of the bearing which overhung the posterior part of the tibial component was calculated.

There was no significant posterior overhang in knees with medial implants. Knees with lateral domed implants exhibited overhang at flexion angles beyond 60°, the magnitude of which increased with increasing flexion angle, reaching a maximum of 50% of the bearing length at 140° (range 0-140°). This demonstrates a clear difference between the kinematics, and prevalence and extent of posterior bearing overhang between medial and lateral OUKRs.
Original languageEnglish
JournalJournal of Orthopaedic Research
Publication statusAccepted/In press - 16 Apr 2019

Keywords

  • unicompartmental knee replacement
  • Mobile bearing

Cite this

Posterior Bearing Overhang Following Medial and Lateral Mobile Bearing Unicompartmental Knee Replacements : A prospective Cohort Study. Level 2 evidence. / Martin, Benjamin; Pegg, Elise; Van Duren, Bernard; Mohammad, Hassan; Pandit, Hemant; Mellon, Stephen J; Murray, David.

In: Journal of Orthopaedic Research, 16.04.2019.

Research output: Contribution to journalArticle

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abstract = "This study explores the extent of bearing overhang following mobile bearing Oxford unicompartmental knee replacement. The Oxford components are designed to be fully congruent, however knee movements involve femoral rollback, which may result in bearing overhang at the posterior margin of the tibial implant, with potential implications for; pain, wear, and dislocation. Movement is known to be greater, and therefore posterior overhang more likely to occur, with; lateral compared to medial implants, anterior cruciate ligament deficiency, and at extremes of movement. 32 knees with medial, and 20 with domed lateral, unicompartmental knee implants (Oxford Phase III, Zimmer Biomet) had sagittal plane knee fluoroscopy during step-up and forward lunge exercises. Within the 32 medial implants, 16 were ACL deficient, and 16 ACL intact. The bearing position was inferred from the relative position of the femoral and tibial components. Based on the individual component sizes and geometry the extent the posterior part of the bearing which overhung the posterior part of the tibial component was calculated. There was no significant posterior overhang in knees with medial implants. Knees with lateral domed implants exhibited overhang at flexion angles beyond 60°, the magnitude of which increased with increasing flexion angle, reaching a maximum of 50{\%} of the bearing length at 140° (range 0-140°). This demonstrates a clear difference between the kinematics, and prevalence and extent of posterior bearing overhang between medial and lateral OUKRs.",
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