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Physiologic bowing in children: an analysis of the pendulum mechanism
E B MacMahon1, D V Carmines, R N Irani
1Department of Orthopaedic Surgery, Georgetown University Medical Center, Washington, D.C. 20007, USA.
Insights
Physiologic bowing in infants, termed "pendulum-like swing," helps equalize growth in the lower limb. This analysis of infant leg alignment can aid in diagnosing limb pathologies masked by knee angle alone.
Area of Science:
- Pediatric Orthopedics
- Biomechanics
- Human Physiology
Background:
- Infants commonly exhibit physiologic bowing of the legs.
- The lower extremity undergoes age-related changes in weight, bone length, and alignment.
- The characteristic varus to valgus to neutral movement of the knee's mechanical axis is termed "pendulum-like swing".
Purpose of the Study:
- To investigate the reasons for physiologic bowing in infants.
- To understand the function of the "pendulum-like swing" in infant lower limb development.
- To establish a method for diagnosing lower limb pathologies in children.
Main Methods:
- Construction of an "average" infant leg model (ages 1-8 years) using anthropomorphic data.
- Calculation of bending moments on five anatomic levels of the limb about the knee.
- Analysis of limb alignment and its relation to growth and pathology.
Main Results:
- Bending moments were calculated at various anatomic levels of the infant leg.
- During specific growth periods, bending moments were found to be minimal.
- This analysis can identify pathologies that may be "masked" by standard knee angle measurements.
Conclusions:
- The "pendulum-like swing" mechanism is crucial for equalizing physeal growth about the knee as children begin to stand.
- The calculation of bending moments offers a diagnostic tool for lower limb pathologies.
- This biomechanical analysis enhances the diagnosis of pediatric lower limb conditions.
Abstract:
Prompted by common observations, we investigated why physiologic bowing occurs in infants and what purpose is served by its characteristic varus to valgus to neutral movement of the mechanical axis of the knee which we term "pendulum-like swing" in the frontal plane. Anthropomorphic data were readily available on age-related increase in weight, femoral and tibial lengths, and changes in lower extremity to allow construction of an "average" leg representing "normal" limb alignment of a growing infant male aged 1-8 years. This enabled us to calculate the bending moments on five anatomic levels of the limb about the knee; more important, during some growth periods the bending moments are minimal and may be used to diagnose pathologies of the lower limb. This form of analysis may prove useful in pathologies in which mechanisms serve to "mask" problems diagnosed on the basis of knee angle alone. When the child begins to stand, the pendulum mechanism is needed to equalize physeal growth about the knee.