Background: Full-length standing anteroposterior radiograph is a standard protocol to evaluate the lower limb alignment in frontal plane. However, most people tend to stand or walk with feet pointing outward. The purpose of this study is to assess the femorotibial relationship as the posture changes from patellae-forward stance for the conventional technique of a full-length standing anteroposterior radiograph to a toe-out quiet stance using a fluoroscope.
Methods: Femoral and tibial rotation and femorotibial rotation were measured in 60 healthy lower limbs using fluoroscopy during postural change from patellae-forward stance to toe-out quiet stance.
Results: The average toe-out angle was 21.4°. The average femoral, tibial, and femorotibial rotations during postural change were 6.1°, 4.0°, and 2.1°, respectively (p = 0.000). The correlation coefficient for femoral and tibial rotation was 0.747 (p = 0.000). The correlation coefficient for femoral and femorotibial rotation was 0.670 (p = 0.000), and for tibial and femorotibial rotation was 0.006 (p = 0.962). The correlation between toe-out angle and femorotibial rotation was statistically significant (r2 = 0.096, p = 0.016). The correlations between toe-out angle and femoral rotation, and between toe-out angle and tibial rotation were not statistically significant (r2 = 0.047, p = 0.095, and r2 = 0.000, p = 0.9, respectively).
Conclusions: The subject's posture significantly affects the femorotibial relationship. When a subject changes posture from a patellae-forward stance to a toe-out quiet stance, the femur rotates internally on the tibia.
Level of evidence: Diagnostic, level II.