Lower limb alignment in children: reference values based on a full-length standing radiograph.

Area of Science:

• Orthopedics
• Pediatric Radiology
• Biomechanical Analysis

Background:

• Full-length standing anteroposterior radiographs are standard for lower limb alignment assessment.
• Established adult reference values for frontal plane deformity may not apply to pediatric populations.
• Pediatric lower limb alignment undergoes significant changes during growth.

Purpose of the Study:

• To establish age-specific reference values for frontal plane alignment and joint orientation angles in children.
• To analyze the developmental changes in lower limb alignment from infancy through adolescence.
• To provide normative data for pediatric lower extremity radiographic evaluation.

Main Methods:

• Retrospective analysis of standing full-length lower extremity radiographs in 253 children (1-18 years).
• Calculation of parameters including mechanical axis deviation, lateral distal femoral angle (LDFA), and medial proximal tibial angle (MPTA).
• Descriptive statistics and regression analysis to correlate age with alignment parameters.

Main Results:

• Lower limb alignment transitions from varus to valgus between ages 1 and 3 years.
• Varus alignment in 1-2 year olds is linked to distal femur varus (mean LDFA 95°).
• Valgus alignment by age 3 is due to decreasing femur varus and increasing proximal tibia valgus (mean MPTA 91°).
• Alignment angles normalize to adult ranges after age 7.
• Mechanical axis remains central in the knee for children over 1 year.

Conclusions:

• The varus-to-valgus shift in pediatric lower limbs (1-4 years) is primarily driven by changes in distal femur orientation.
• Age-specific reference values are essential for interpreting lower extremity joint angles in children under 7 years.
• Adult reference values are not suitable for pediatric populations in this age group.