Kinematic characteristics of the tibiofemoral joint during a step-up activity

- The tibial contact points moved anteriorly during the step-up, similar to TEA, but not GCA
- Medial-pivoting was not observed during step-up activity
- Selection of coordinate systems changed knee joint kinematics description dramatically

The step-up activity (stair-ascending) is an important daily function of the knee. This study aimed to investigate the articular cartilage contact kinematics on both tibial and femoral cartilage surfaces and describe the femoral condylar motion using the transepicondylar axis (TEA) and the geometric center axis (GCA) during a step-up activity. Twenty-one healthy subjects were included and their knee joint models were reconstructed using MR images. A single-stair step-up activity was imaged using a dual-fluoroscopic imaging system. Three-dimensional knee joint contact points were determined and projected onto the tibial plateau and femoral condylar surfaces. The contact points on the medial and lateral tibial plateau moved anteriorly (by 13.5 ± 3.2 and 10.7 ± 5.0 mm, respectively, p > 0.05) with knee extension. The contact points on the medial and lateral femoral condyle moved from the posterior to the anterior portion (by 32.2 ± 4.9 mm and 25.5 ± 4.2 mm, respectively, p < 0.05) and were located on the inner half of the femoral cartilage throughout the activity. The data on articular contact kinematics and the femoral condylar motion described using the TEA and GCA indicated that the medial and lateral compartments had similar motion patterns during the step-up activity. The knee does not demonstrate a medial-pivoting motion character during the step-up activity. The data may provide insight to contemporary TKA development.