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. 2023 Jun 1;43(6):e220177. doi: 10.1148/rg.220177

Figure 14.

Normal patellofemoral kinematics. As the knee flexes and extends, the patella tilts, rotates, and shifts with respect to the trochlea, incorporating six degrees of freedom of patellar movement. Measurements of patellar height vary at different degrees of knee flexion and can confound evaluation of the patella alta. Standard lateral radiographs used to define the normal range of patellar height are obtained at 30° of flexion. Standard CT and MR images are obtained with the knee in extension; therefore, the patella is normally positioned more proximally relative to the trochlea.

Normal patellofemoral kinematics. As the knee flexes and extends, the patella tilts, rotates, and shifts with respect to the trochlea, incorporating six degrees of freedom of patellar movement. Measurements of patellar height vary at different degrees of knee flexion and can confound evaluation of the patella alta. Standard lateral radiographs used to define the normal range of patellar height are obtained at 30° of flexion. Standard CT and MR images are obtained with the knee in extension; therefore, the patella is normally positioned more proximally relative to the trochlea.