Effect of different tibial cuts on femorotibial knee kinematics in TKA in the constitutional varus knee
ESSKA Academy. Faschingbauer M. Nov 8, 2019; 284395; epEKA-66 Topic: Biomechanics
Martin Faschingbauer
Martin Faschingbauer
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Effect of different tibial cuts on femorotibial knee kinematics in TKA in the constitutional varus knee

ePoster - epEKA-66

Topic: TKA

Faschingbauer M.1, Dürselen L.2, Seitz A.2, Hacker S.2, Reichel H.1
1University of Ulm, Orthopedic Surgery, Ulm, Germany, 2University of Ulm, Institute of Orthopedic Research and Biomechanics, Centre for Trauma Research Ulm, Ulm, Germany

Aims: Due to a satisfaction rate of around 80% after TKA, in addition to the standard alignment options (mechanical and anatomical alignment), further alignment options such as kinematic alignment and constitutional alignment have been described. There is evidence in the current literature that patients treated with constitutional or kinematic aligned TKAs show better outcome scores. The underlying kinematic changes are not yet described. The present study aimed to compare the effects of different tibial cuts on knee kinematics and to compare them with the natural, constitutional varus-knee.
Methods: Seven cadaveric knee joints with constitutional varus alignment were examined in the native state, after implantation of a 0° tibia-cut CR TKA, 3° and 6° tibial cut in an established knee joint simulator. In a flexion movement, up to 100°, the effects on varus-alignment, on the femorotibial rollback and on the femorotibial rotation were determined. Besides, the natural varus knee joint and the different varus cuts were compared using mean comparisons.
Results: In the tibiofemoral joint, the TKAs with the varus cut 3° and 6° show the greatest differences to the constitutional varus knee, whereas the TKA with a 0° tibial cut is most similar to the natural knee joint. In the femoral rollback in the medial compartment, the natural knee joint shows the highest translation/mobility (5.7-12.5mm). The varus cut 6° has an explicit restriction in the translation of the medial compartment (2-3.2mm).
In contrast, the longest translations can be observed in the lateral compartment with the varus cut 0°, followed by the varus cuts 3° and 6° and the natural knee joint. In the tibiofemoral rotation, the 0° and 3° varus cuts across all load cases show the least difference to the natural knee joint (3.4°), with the 0° varus cut showing a higher absolute internal rotation of the tibia than the natural knee joint.
Conclusions: The improved outcome parameters in the kinematic aligned TKAs described in the literature cannot be completely explained with the changes in the tibiofemoral joint. From a biomechanical point of view, the mechanical alignment (= varus-cut 0°) remains to be taken into account due to the lower varus deviation demonstrated in the present study and the thus uniform medio-lateral load distribution (as well as the presumably associated lower wear problem and aseptic loosening tendency). From a kinematic point of view, it is not recommended to exceed a 3° cut on the tibia.
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