The hip-knee-ankle angle in children: reference values based on a full-length standing radiograph

Area of Science:

• Pediatric Orthopedics
• Biomechanical Analysis
• Radiographic Measurement

Background:

• Lower limb alignment undergoes significant changes during childhood.
• Established reference values for adult hip-knee-ankle angles exist, but are lacking for pediatric populations.
• The hip-knee-ankle angle, a measure of mechanical femoral-tibial alignment, is crucial for assessing lower limb development.

Purpose of the Study:

• To establish reference values for the hip-knee-ankle angle in children.
• To assess the relationship between the hip-knee-ankle angle and the anatomic femoral-tibial angle in pediatric populations.
• To provide age-specific data for pediatric lower limb alignment.

Main Methods:

• Analysis of standing full-length lower extremity radiographs from 253 children (aged 1 to <18 years).
• Measurement of the hip-knee-ankle angle on radiographs of unaffected lower extremities.
• Simple regression analyses to determine the correlation between hip-knee-ankle and anatomic femoral-tibial angles.

Main Results:

• Mean hip-knee-ankle angles varied by age: +3.6° (varus) in 1-2 year olds, -2.5° (valgus) in 2-3 year olds.
• Children over seven years old showed a mean angle of +0.3° (varus), similar to adult values (+1.2° varus).
• A strong linear relationship (r=0.87) was found between hip-knee-ankle and anatomic femoral-tibial angles in children; the difference remained constant with age.

Conclusions:

• Pediatric hip-knee-ankle angle reference values approach adult North American values after age seven.
• Distinct angular measurements were observed in children under seven compared to adults.
• Age-specific reference values for both hip-knee-ankle and anatomic femoral-tibial angles are recommended for children under seven.