Differences between Sagittal Femoral Mechanical and Distal Reference Axes Should Be Considered in Navigated TKA

Abstract

In computer-assisted TKA, surgeons determine positioning of the femoral component in the sagittal plane based on the sagittal mechanical axis identified by the navigation system. We hypothesized mechanical and distal femoral axes may differ on lateral views and these variations are influenced by anteroposterior bowing and length of the femur. We measured angles between the mechanical axis and distal femoral axis on 200 true lateral radiographs of the whole femur from 100 adults. We used multivariate linear regression to identify predictors of differences between the axes. Depending on the method used to define the two axes, the mean angular difference between the axes was as much as 3.8°and as little as 0.0°, with standard differences ranging from 1.7°to 1.9°. Variation between the two axes increased with increased femoral bowing and increased femoral length. Surgeons should consider differences between the mechanical axes and distal femoral axes when they set the sagittal plane position of a femoral component in navigated cases. Our findings also may be relevant when measuring rotation of the femoral component in the sagittal plane from postoperative radiographs or when interpreting femoral component sagittal rotation results reported in other studies.

Imageless Navigation System Does Not Improve Component Rotational Alignment in Total Knee Arthroplasty

“…In addition, the dis-crepancies between radiographic and navigation measurements may have resulted from differences in weight-bearing status and presence of knee deformities [102,104,105]. Postoperative full-length radiographic measurements have inherent limitations [102][103][104][105][106], which we believe affected our results substantially.…”

Improved Accuracy of Alignment With Patient-specific Positioning Guides Compared With Manual Instrumentation in TKA

“…First, coronal alignment and standing LLRs are the traditional gold standard for assessment of TKA [60]. However, with the recent widespread introduction of threedimensional imaging and CAN, there is additional focus on sagittal and axial alignment [19,30,77,88]. While postoperative CT is routinely acquired to evaluate component rotation in patients with patellar maltracking issues [6], the costly nature of routine postoperative scanning is prohibitive in large-scale studies.…”

Clinical Faceoff: Do We Need Special Strategies for Asian Patients with TKA?

“…We should make an adequate bone bed for the anterior flange of the femoral component with proper cementing technique. Furthermore, caution should be taken to avoid anterior notching in knees with severe femoral anterior bowing, particularly when using computer assisted navigation [4,13,17]. Postoperative rehabilitation is also impo rtant.…”