TKA Sagittal Alignment with Navigation Systems and Conventional Techniques Vary Only a Few Degrees

Navigation systems have been developed to achieve more reliable prosthetic alignment in TKAs. However, the component alignment in the sagittal plane is reportedly less reliable than in the coronal plane even with navigation systems. We measured and compared sagittal prosthetic alignments for TKAs with the conventional technique and three navigation approaches to establish reference frames, using radiographs of the entire lower extremity while standing. The sagittal alignments simulated on the radiographs with the conventional technique and navigation systems differed by a mean of 2A degrees to 4A degrees. Use of navigation systems resulted in a mean of 1A degrees to 4A degrees hyperextension between the femoral and tibial components and use of the conventional technique resulted in a mean of 1A degrees flexion. Use of different reference points on the distal femoral condyle for the navigation systems resulted in differences of as much as 3A degrees alignment in the sagittal plane. Although optimal prosthetic alignment for TKA in the sagittal plane is unknown, surgeons and technicians using navigation systems should be aware of this difference in the sagittal plane and the risk of hyperextension between the femoral and tibial components, which might be associated with osteolysis and anterior post-cam impingement.