Methodist Center for Orthopaedic Surgery, 6550 Fannin, Suite 2600, Houston, TX, 77030, USA.
Clin Orthop Relat Res. 2014 Jan;472(1):121-5. doi: 10.1007/s11999-013-3047-y.
Traditionally, the placement of the tibial component in total knee arthroplasty (TKA) has focused on maximizing coverage of the tibial surface. However, the degree to which maximal coverage affects correct rotational placement of symmetric and asymmetric tibial components has not been well defined and might represent an implant design issue worthy of further inquiry.
QUESTIONS/PURPOSES: Using four commercially available tibial components (two symmetric, two asymmetric), we sought to determine (1) the overall amount of malrotation that would occur if components were placed for maximal tibial coverage; and (2) whether the asymmetric designs would result in less malrotation than the symmetric designs when placed for maximal coverage in a computer model using CT reconstructions.
CT reconstructions of 30 tibial specimens were used to generate three-dimensional tibia reconstructions with attention to the tibial anatomic axis, the tibial tubercle, and the resected tibial surface. Using strict criteria, four commercially available tibial designs (two symmetric, two asymmetric) were placed on the resected tibial surface. The resulting component rotation was examined.
Among all four designs, 70% of all tibial components placed in orientation maximizing fit to resection surface were internally malrotated (average 9°). The asymmetric designs had fewer cases of malrotation (28% and 52% for the two asymmetric designs, 100% and 96% for the two symmetric designs; p < 0.001) and less malrotation on average (2° and 5° for the asymmetric designs, 14° for both symmetric designs; p < 0.001).
Maximizing tibial coverage resulted in implant malrotation in a large percentage of cases. Given similar amounts of tibial coverage, correct rotational positioning was more likely to occur with the asymmetric designs.
Malrotation of components is an important cause of failure in TKA. Priority should be given to correct tibial rotational positioning. This study suggested that it is easier to balance rotation and coverage with asymmetric tibial baseplates; clinical research will need to determine whether the observed difference affects patellar tracking, loosening rates, or the likelihood of revisions after TKA.
传统上，全膝关节置换术（TKA）中胫骨部件的放置侧重于最大限度地覆盖胫骨表面。然而，最大限度地覆盖会在多大程度上影响对称和非对称胫骨部件的正确旋转放置尚未得到很好的定义，这可能代表一个值得进一步研究的植入物设计问题。
问题/目的：我们使用四种市售胫骨组件（两种对称，两种非对称），旨在确定：（1）如果为了获得最大的胫骨覆盖而放置组件，会发生多大程度的整体旋转不良；（2）在使用 CT 重建的计算机模型中，为了获得最大的覆盖范围，非对称设计是否会导致比对称设计的旋转不良程度更小。
使用 30 个胫骨标本的 CT 重建来生成三维胫骨重建，注意胫骨解剖轴、胫骨结节和切除的胫骨表面。使用严格的标准，将四种市售的胫骨设计（两种对称，两种非对称）放置在切除的胫骨表面上。检查由此产生的组件旋转。
在所有四种设计中，70%的胫骨组件在最大限度地贴合切除表面的方向上被内部旋转不良（平均 9°）。非对称设计的旋转不良病例较少（两种非对称设计分别为 28%和 52%，两种对称设计分别为 100%和 96%；p <0.001），平均旋转不良程度较小（两种非对称设计分别为 2°和 5°，两种对称设计均为 14°；p <0.001）。
最大限度地覆盖胫骨会导致很大一部分情况下植入物旋转不良。在类似的胫骨覆盖量下，非对称设计更有可能实现正确的旋转定位。
组件的旋转不良是 TKA 失败的一个重要原因。应优先考虑正确的胫骨旋转定位。本研究表明，使用不对称胫骨基板更容易平衡旋转和覆盖；临床研究需要确定观察到的差异是否会影响髌骨跟踪、松动率或 TKA 后的翻修可能性。
