Department of Orthopaedic Surgery, University of Regensburg, Regensburg, Germany.
Montanuniversität Leoben, Leoben, Austria.
Knee Surg Sports Traumatol Arthrosc. 2018 Nov;26(11):3311-3316. doi: 10.1007/s00167-018-4875-9. Epub 2018 Feb 17.
Intramedullary rods are widely used to align the distal femoral cut in total knee arthroplasty. We hypothesised that both coronal (varus/valgus) and sagittal (extension/flexion) cutting plane are affected by rotational changes of intramedullary femoral alignment guides.
Distal femoral cuts using intramedullary alignment rods were simulated by means of a computer-aided engineering software in 4°, 6°, 8°, 10°, and 12° of valgus in relation to the femoral anatomical axis and 4° extension, neutral, as well as 4°, 8°, and 12° of flexion in relation to the femoral mechanical axis. This reflects the different angles between anatomical and mechanical axis in coronal and sagittal planes. To assess the influence of rotation of the alignment guide on the effective distal femoral cutting plane, all combinations were simulated with the rod gradually aligned from 40° of external to 40° of internal rotation.
Rotational changes of the distal femoral alignment guides affect both the coronal and sagittal cutting planes. When alignment rods are intruded neutrally with regards to sagittal alignment, external rotation causes flexion, while internal rotation causes extension of the sagittal cutting plane. Simultaneously the coronal effect (valgus) decreases resulting in an increased varus of the cutting plane. However, when alignment rods are intruded in extension or flexion partly contradictory effects are observed. Generally the effect increases with the degree of valgus preset, rotation and flexion.
As incorrect rotation of intramedullary alignment guides for distal femoral cuts causes significant cutting errors, exact rotational alignment is crucial. Coronal cutting errors in the distal femoral plane might result in overall leg malalignment, asymmetric extension gaps and subsequent sagittal cutting errors.
髓内棒被广泛用于全膝关节置换术中对齐股骨远端截骨面。我们假设，冠状面（内翻/外翻）和矢状面（伸直/屈曲）的切割平面都受到髓内股骨对线导向器旋转变化的影响。
通过计算机辅助工程软件模拟髓内定位棒在距股骨解剖轴 4°、6°、8°、10°和 12°的外翻和距股骨机械轴 4°伸直、中立以及 4°、8°和 12°的屈曲情况下的股骨远端截骨。这反映了冠状面和矢状面解剖轴和机械轴之间的不同角度。为了评估对线导向器旋转对有效股骨远端切割平面的影响，模拟了所有组合，定位棒从 40°外旋逐渐调整到 40°内旋。
股骨远端对线导向器的旋转变化会影响冠状面和矢状面的切割平面。当对线棒在矢状面对齐时中立插入时，外旋会导致屈曲，而内旋会导致矢状切割平面的伸展。同时，冠状面的影响（外翻）减小，导致切割平面的内翻增加。然而，当对线棒在伸直或屈曲时部分插入时，观察到相反的效果。一般来说，随着预设的外翻程度、旋转和屈曲程度的增加，效果会增加。
由于不正确的髓内对线导向器旋转会导致股骨远端切割产生显著的切割误差，因此精确的旋转对线至关重要。股骨远端切割平面的冠状面切割误差可能导致整体下肢对线不良、不对称的伸直间隙和随后的矢状面切割误差。
