Femur Positioning in Navigated Total Knee Arthroplasty

Abstract

Navigated total knee arthroplasty (TKA) results in better restoration of neutral mechanical axis than does the conventional technique. Nevertheless, coronal malalignment has not been eliminated. It is yet unknown whether errors in implant positioning occur more on the femoral side, more on the tibial side, or equally on both sides. The hypothesis of this study was that a predominance of coronal component malalignment exists on the tibial side in navigated tibia-first TKA.Fifty-seven consecutive navigated (OrthoPilot; B. Braun Aesculap, Tuttlingen, Germany) TKAs were included in this retrospective study. Pre- and postoperative digital whole-leg standing radiographs were analyzed. Coronal alignment was measured for the whole leg pre- and postoperatively. Lateral distal femur angle and medial proximal tibia angle were analyzed on the preoperative radiographs. On the postoperative radiographs, coronal alignment of the femoral and tibial components were measured separately in reference to the tibial and femoral mechanical axis. The coronal alignment improved from 8.2° ± 3.7° preoperatively to 1.1° ± 1.2° postoperatively, with 5 (8%) outliers outside the 3° window. The femoral component was malaligned (0.6° ± 0.6°), whereas the tibial component showed a significantly higher deviation from the mechanical axis of 1.0° ± 1.1° (P=.009). The femoral component was positioned more precisely than the tibial component. The latter influences gap management in the tibia-first technique and may thereby have a relevant effect on joint stability. Accuracy of the surgical technique and differences in the mathematical algorithm for the determination of landmarks are possible reasons for the difference in precision between the femoral and tibial component positioning.

Gap-balancing technique combined with patient-specific instrumentation in TKA

“…Reliable use of the gap-balancing technique with a sufficiently accurate tibial cut is therefore ensured. Femoral rotation is more accurate if it has already been balanced in extension, and avoids secondary rotational malalignment of the femoral component due to a varus or valgus malalignment of the tibial component [43,44]. Raising the joint line by up to 5 mm is then possible without having a detrimental effect [40,[45][46][47].…”

Small Improvements in Postoperative Outcome with Gap Balancing Technique Compared with Measured Resection in Total Knee Arthroplasty

“…However, a highly accurate proximal tibial cut is required for the GB technique because initial tibial alignment errors will be carried through to all subsequent cuts [ 26 ]. There is evidence that secondary rotational malalignment of the femoral component can be caused by malalignment of the tibial component in the coronal plane [ 27 ]. We previously presented a study that demonstrated that the use of patient-specific instrumentation (PSI) may be advantageous to achieve optimal component positioning.…”

Small Improvements in Mechanical Axis Alignment Achieved With MRI versus CT-based Patient-specific Instruments in TKA: A Randomized Clinical Trial

“…Innovations including navigation and patientspecific instrumentation have been introduced to theoretically improve the accuracy of alignment obtained with conventional instrumentation [11,14,35,40]. The evaluation of navigation has shown that, although it is possible to improve accuracy in the coronal plane [12,23,40], it is not as effective in improving accuracy of rotation or tibial slope [11,12,17,31].…”