ROTATIONAL ALIGNMENT OF THE TIBIAL COMPONENT IN TKA IS BETTER AT THE MEDIAL THIRD OF TIBIAL TUBEROSITY THAN AT THE MEDIAL BORDER

Abstract

Background: Correct rotational alignment of the femoral and tibial component is an important factor for successful TKA. The transepicondylar axis is widely accepted as a reference for the femoral component. There is no such reference for the tibial component. CT scans were used in this study to measure which tibial landmark most reliably reproduces a correct femoro-tibial rotational alignment in TKA. Furthermore, the impact of computer-assisted navigation on rotational alignment is investigated.

Materials and Methods: After informed consent, 80 patients were randomized to receive either navigated or conventional TKA. All patients received a cemented, unconstrained, cruciate-retaining TKA with a rotating platform. CT scans were performed 5–7 days postoperatively but before discharge. The rotational variance between the femoral and tibial components was measured.

Results: There was notable rotational variance between the femoral and tibial components in both groups. In the navigated group, the median variance was 1.2° relative external rotation of the femur (range: 16.2° relative external to 12.7° relative internal rotation of the femur). In the conventional group, the median variance was 1.7° relative internal rotation of the femur (range: 9.0° relative external to 14.4° relative internal rotation of the femur). Using the medial third of the tuberosity as reference for tibial rotational alignment, 67.5% of all TKA had a femoro-tibial variance within ± 5°, 85% within ± 10° and 97.5% within ± 20°. Using the medial border of the tibial tubercle as reference this variance was greater, 3.8% had a femoro-tibial variance within ± 5°, 15% within ± 10° and 68.8% within ± 20°.

Conclusion: Using fixed bone landmarks for rotational alignment leads to a notable variance between femoral and tibial component. Computer-assisted navigation did not reduce this variance.

Referencing the tibial rotation on a line from the lateral border of the medial third of the tibial tubercle to the center of the tibial tray resulted in a better femoro-tibial alignment than using the medial border of tibial tubercle as landmark. Surgeons using fixed bearings with a high conformity between the inlay and the femoral component should be aware of this effect to avoid premature polyethylene wear.