Department of Orthopaedic Surgery and Joint Surgery Centre, Takatsuki General Hospital, Osaka, Japan.
Department of Orthopaedic Surgery and Joint Surgery Centre, Takatsuki General Hospital, Osaka, Japan; Department of Orthopaedic Surgery, Graduate School of Medicine, Kobe University, Kobe, Japan.
Orthop Traumatol Surg Res. 2023 Dec;109(8):103598. doi: 10.1016/j.otsr.2023.103598. Epub 2023 Mar 16.
A 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?
The femoral component size and the bearing thickness could affect the MLD and MRD.
The 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.
The 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 thicker bearing. Similarly, the RRD decreased with a smaller femoral size or a thicker bearing thickness in all directions.
Increased 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.
III; comparative computer simulation study.
当关节松弛度大于跳跃高度，即底面和轴承最高点（每侧上轴承表面的最高点）之间的高度差时，活动轴承可能会脱位。因此，应避免因间隙平衡不当而导致的明显松弛。然而，一旦轴承在胫骨组件上垂直旋转，轴承可能会在比跳跃高度更小的松弛度下脱位。我们通过数学计算了脱位所需的松弛度（RLD）和脱位所需的轴承旋转度（RRD）。本研究旨在回答以下问题：1）股骨组件尺寸和轴承厚度是否会影响 RLD 和 RRD？
股骨组件尺寸和轴承厚度可能会影响 MLD 和 MRD。
使用制造商提供的轴承尺寸，以股骨组件尺寸、轴承厚度和方向（前、后和内/外侧）为二维变量，计算 RLD 和 RRD。
前向 RLD 为 3.4 至 5.5mm，后向 RLD 为 2.3 至 3.8mm，内/外侧 RLD 为 1.4 至 2.4mm。RLD 随股骨尺寸减小或轴承厚度增加而减小。同样，在所有方向上，RRD 随股骨尺寸减小或轴承厚度增加而减小。
增加轴承厚度和减小股骨组件尺寸会减小 RLD 和 RRD，这将增加脱位的风险。因此，选择尽可能大的股骨组件和尽可能薄的轴承有助于预防脱位。
III；比较计算机模拟研究。
