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


This study explores the extent of bearing overhang following mobile bearing Oxford unicompartmental knee replacement (OUKR) (Oxford Phase 3, Zimmer Biomet). 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 (ACL) deficiency (ACLD) compared to ACL intact (ALCI), and at extremes of movement. Twenty-four medial, and 20 domed lateral, OUKRs underwent sagittal plane knee fluoroscopy during step-up and forward lunge exercises. The bearing position was inferred from the relative position of the femoral and tibial components. On the basis of 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
Pages (from-to)1938-1945
Number of pages8
JournalJournal of Orthopaedic Research
Issue number9
Early online date6 May 2019
Publication statusPublished - 1 Sep 2019


  • mobile bearing
  • posterior bearing overhang
  • unicompartmental knee replacement

ASJC Scopus subject areas

  • Orthopedics and Sports Medicine

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