Proposed Geometrical Tool for Cases of Laterally Adapted Tibial Tubercle during Total Knee Replacement

The alignment of tibial component in total knee replacement operation must be achieved in three planes to ensure optimum results. In coronal plane, the alignment depends on three anatomical landmarks. These landmarks are tibial tuberosity, leg shin, and midtalar point. In eastern community, people get used to sit cross-legged which causes additional tension in the quadriceps muscle which is attached distally to the tibial tuberosity. This tension causes adaptation of the tuberosity laterally. Tuberosity adaptation causes the three anatomical landmarks being not collinear. In this work, eight cases of lateral adapted tubercle were diagnosed of this condition before the surgery and their X-ray images after the surgery were checked regarding tibial alignment. Tibial alignment has been checked by measuring the medial proximal tibial angle (MPTA) which is the angle between the mechanical tibial axis and the tibial component plateau. MPTAs for the eight cases were (86.9°-93.6°). Three cases had MPTA less than 90° indicating varus alignment and five of them had MPTA more than 90° indicating valgus alignment. A geometrical tool was designed using the DesignSpark Mechanical software as a proposed solution to solve the adaptation problem. The tool can give a method for fixing the tibial component precisely without any varus\valgus malalignment.