A landmark-based 3D analysis reveals a narrower tibial plateau and patella in trochlear dysplastic knees

Purpose The trochlear dysplastic femur has a specific morphotype previously characterised by not only dysplastic features of the trochlea but also by specific features of the notch and posterior femur. In this study the morphology of the tibia and patella was investigated to gain further insight in the complete geometrical complexity of the trochlear dysplastic knee. Methods Arthro-CT scan-based 3D models of 20 trochlear dysplastic and 20 normal knees were uniformly scaled and landmarks and landmark-based reference planes were created to quantify a series of morphometric characteristics of the tibia and patella. Results In the mediolateral direction, the 3D-analysis revealed a 3% smaller medial tibial plateau (30.4 +/- 1.6 mm vs 31.5 +/- 1.6 mm), a 3% smaller overall width of the tibial plateau (73.6 +/- 2.0 mm vs 75.7 +/- 2.0 mm), a 16% smaller medial facet (17.3 +/- 2.2 mm vs 20.1 +/- 1.3 mm) and a 4% smaller overall width of the patella (41.7 +/- 2.5 mm vs 43.4 +/- 2.3 mm) in trochlear dysplastic knees. In the anteroposterior direction, the lateral tibial plateau of trochlear dysplastic knees was 5% larger (37.2 +/- 2.3 mm vs 35.5 +/- 3.1 mm). A correlation test between the width of the femur and the width of the tibia revealed that trochlear dysplastic knees show less correspondence between the femur and tibia compared to normal knees. Conclusion Significant differences in the morphology of the tibial plateau and patella were detected between trochlear dysplastic and normal knees. Both in the trochlear dysplastic tibial plateau and patella a narrower medial compartment leads to a significant smaller overall mediolateral width. These findings are important for the understanding of knee biomechanics and the design of total knee arthroplasty components.