Abstract
Purpose:
Accepted landmarks for determining femoral component rotation in total knee arthroplasty (TKA) include the posterior condyles, Whiteside’s line, arbitrary three to four degrees of external rotation, and transepicondylar axis (TEA). All methods require anatomical identification, which may be variable. The purpose of this study was to radiologically evaluate femoral component rotation (CT analysis) based on a method that references to the tibial shaft axis and balanced flexion tension without identification of femoral anatomical landmarks.
Methods:
Out of a cohort of 3058 mobile bearing low contact stress TKA, CT scans of 38 randomly selected well functioning TKA were evaluated to determine femoral component positioning. Spiral CT scans of the femoral epicondylar region with four mm cuts were performed to accurately identify medial and lateral femoral epicondyles. Rotational alignment was measured in relation to the transepicondylar axis using CT-implemented software by two independent radiologists.
Results:
Mean femoral rotational alignment was parallel to the TEA (average 0. 3 degrees internal rotation) ranging from six degrees internal to four degrees external rotation. All thirty-eight cases had satisfactory clinical results, range of motion of over 90°, and showed perfect patello-femoral tracking and patellar congruency on axial views.
Conclusions:
Femoral rotation position based on tibial shaft axis and balanced flexion tension gap is patient specific, reproducible and results in predictable femoral rotational positioning and patella tracking. CT analysis in this study confirms that the tibial shaft axis method produces a consistent femoral component positioning that relates accurately to the TEA. Tibial shaft axis method avoids the need for arbitrary landmark identification, placing the femoral component predictably in an optimum position in relation to the tibia and patella.
Address for correspondence: jgboldt@hotmail.com
Schulthess Klinik, Zurich, Switzerland. Lehigh Valley Hospital, Allentown, PA, USA
