抄録
This study examined the influence of knee flexion in a standing position on the patellar rotation angle in the frontal plane using radiographs. The study included 20 limbs of 10 healthy adults (mean age: 26.5 ± 3.2 years). The participants were instructed to randomly change the flexion angles of both knees in a standing position from 0° to 60° at intervals of 10° and frontal images were captured. The inward and outward movements of the lower part of the patella were regarded as external and internal rotations, respectively, and the patellar rotation angle in the frontal plane was calculated with a view to clarifying the influence of changes in knee flexion angle on the patellar rotation angle in the frontal plane, as well as the level of change in the patellar rotation angle with changes in knee flexion angle of 10°. The patellar rotation angle in the frontal plane showed a tendency to externally rotate with increase in the knee flexion angle. The increase in the patellar rotation angle was more marked at knee flexion angles of 40°, 50°, and 60° than at 0° (p<0.05). Furthermore, the external patellar rotation angle increased more markedly at knee flexion angles of 0° and 10° than at the other angles (p<0.05). These results may be explained by the lower extremity rotating internally during knee flexion, with regard to the position of the femur, consequently pulling the lower part of the patella inward through the patellar ligament. Contraction of the vastus medialis may also have acted to externally rotate the patella. Considering that the contact area between the patella and intercondylar notch of the femur is small at a knee flexion angle of 0°, the change in the external patellar rotation angle is likely to peak in the early stage of knee flexion.
