Les ménisques mobiles peuvent se luxer avec des composants fémoraux plus petits et des composants méniscaux plus épais après arthroplastie unicompartimentale médiale du genou de type Oxford

Abstract

BackgroundA mobile bearing can dislocate when joint laxity is larger than jumping height, the height difference between the bottom and the peak of the bearing (the highest point of the upper bearing surface on each side). Significant laxity due to improper gap balancing should therefore be avoided. However, once the bearing rotates vertically on the tibial component, the bearing can dislocate with smaller laxity than the jumping height. We mathematically calculated the required laxity for dislocation (RLD) and the required rotation of the bearing for dislocation (RRD). The current study addressed the question: 1) could the femoral component size and the bearing thickness affect the RLD and RRD? HypothesisThe femoral component size and the bearing thickness could affect the MLD and MRD. MethodsThe RLD and RRD were calculated using the bearing dimensions provided by the manufacturer with femoral component size, bearing thickness, and directions (anterior, posterior, and medial/lateral) as the variables on a two-dimensional basis. ResultsThe RLD was 3.4 to 5.5mm in the anterior, 2.3 to 3.8mm in the posterior, and 1.4 to 2.4mm in the medial or lateral directions. The RLD decreased with a smaller femoral size or a thinner bearing. Similarly, the RRD decreased with a smaller femoral size or a thinner bearing thickness in all directions. ConclusionsIncreased bearing thickness and decreased femoral component size deceased the RLD and RRD, which would relate to an increased risk of dislocation. Selecting the femoral component as large as possible and the bearing as thin as possible would therefore be helpful in the prevention of dislocation. Level of evidenceIII; comparative computer simulation study.