Abstract
It has become clear that computer navigation in total joint replacement provides more reliable obtaining of a neutral mechanical axis during total knee surgery. The real issue is when one attains a more reliable mechanical axis, is that going to change the clinical outcome both in terms of function and durability? To date, we really haven't been able to answer that question definitively. Is there really a one simple target value for alignment in all patients undergoing total knee replacement?
The constraints on accuracy imposed by our standard total knee instruments and the constraints on assessment imposed by 2-dimensional radiographs made broad, simple targets like a mechanical axis ± 3 degrees reasonable starting points; yet we have not further worked to verify if we can do better. It is naïve to think that the complex motion at the knee occurring in 6 dimensions over time can be reduced to a single static target value like a neutral mechanical axis and have strong predictive value in regard to the success or failure of an individual TKA. We assessed 399 knees of 3 different modern cemented designs at 15 years and found that factors other than alignment were more important than alignment in determining the 15-year survival. That work does not mean that alignment is not important, instead it suggests that either the way we traditionally define malalignment (outside 0 ± 3 degrees) is too imprecise or that the other causes of failure overwhelm malalignment in determine TKA durability.
