2016 年 35 巻 1 号 p. 17-23
Objective: Computer-assisted surgery systems improve alignment accuracy in total knee arthroplasty (TKA) but they are expensive and time-consuming and thus, unpopular. Recently, a portable navigation system has shown excellent performance. We examined the accuracy of distal femoral cutting using an accelerometer-based portable navigation device (KneeAlign® 2; OrthAlign Inc., Aliso Viejo, CA, USA) during TKA.
Methods: We included patients consisting of 78 knees with osteoarthritis, who had undergone TKA using the portable navigation KneeAlign® 2 system. Computed tomography for each lower extremity was performed preoperatively. We simulated the TKA components’ position by using the preoperative planning software Athena® (Soft Cube, Osaka, Japan), and we measured the flexion angle of the femoral component relative to the femoral mechanical axis in the sagittal plane. We performed osteotomy of the distal femur perpendicular to the femoral mechanical axis in the coronal plane and osteotomy of the distal femur using the measured flexion angle of the femoral component relative to the femoral mechanical axis in the sagittal plane.
Results: In all, 93.6% knees had a femoral component alignment within 3°perpendicular to the femoral mechanical axis.
Conclusions: The femur and tibia should be cut perpendicular to the mechanical axis on the coronal plane in TKA. Varus-valgus alignment of more or equal to 3°increased the incidence of component loosening. The portable navigation device ensured an accurate performance of femoral osteotomy in the coronal plane as that performed using other navigation systems. With regard to sagittal plane alignment, the flexion angle between the distal femoral anatomical axis and the mechanical axis showed large interindividual variations and this was measured beforehand using Athena®, and which was confirmed intraoperatively. However, this alignment was primarily achieved visually using the anterior femoral cortex intraoperatively via the conventional method without using a navigation system. Thus, a portable navigation device is useful when performing surgery according to a predetermined plan.