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Exploring infant hip position and muscle activity in common baby gear and orthopedic devices
Safeer F Siddicky1,2, Junsig Wang1, Brien Rabenhorst1
1Department of Orthopaedic Surgery, College of Medicine, University of Arkansas for Medical Sciences, Little Rock, AR.
Insights
Infant positioning impacts hip development. Inward-facing baby carriers may benefit hip biomechanics, while car seats might negatively affect it, warranting further research.
Area of Science:
- Biomechanical analysis of infant musculoskeletal development.
- Pediatric orthopedics and developmental kinesiology.
Background:
- Infant positioning is crucial for hip development, with animal studies suggesting risks from inactive lower extremities.
- Limited experimental research exists on infant hip biomechanics in various positions and devices.
Purpose of the Study:
- To experimentally evaluate hip joint position and lower extremity muscle activity in healthy infants across different common positions and orthopedic devices.
- To compare biomechanical data between orthopedic devices for hip dysplasia and common infant carrying/seating solutions.
Main Methods:
- Utilized surface electromyography (EMG) and marker-based motion capture on 22 healthy infants (4.2±1.6 months).
- Recorded lower extremity muscle activity and kinematics in five conditions: Pavlik harness, Rhino brace, soft-structured baby carrier, held in arms, and car seat.
- Calculated mean filtered EMG signals, muscle activation timing, and hip joint angles.
Main Results:
- Infants in car seats showed significantly lower muscle activity compared to the Pavlik harness.
- Inward-facing baby carriers demonstrated similar hip position to the Pavlik harness, with comparable adductor and gluteus maximus activity but lower quadriceps and hamstring activity.
- Rhino brace showed similar adductor activity but lower hamstring and gluteus maximus activity compared to the Pavlik harness.
Conclusions:
- Inward-facing soft-structured baby carriers may promote healthy infant hip development.
- Prolonged use of supine-lying devices like car seats may negatively impact infant musculoskeletal development.
- Further investigation is required to fully understand the influence of body positioning on infant musculoskeletal development.
Abstract:
Infant positioning in daily life may affect hip development. While neonatal animal studies indicate detrimental relationships between inactive lower extremities and hip development and dysplasia, no research has explored infant hip biomechanics experimentally. This study evaluated hip joint position and lower extremity muscle activity of healthy infants in common body positions, baby gear, and orthopedic devices used to treat hip dysplasia (the Pavlik harness and the Rhino cruiserabduction brace). Surface electromyography(EMG) and marker-based motion capture recorded lower extremity muscle activity and kinematics of 22 healthy full-term infants (4.2±1.6 months, 13M/9F) during five conditions: Pavlik harness, Rhino brace, inward-facing soft-structured baby carrier, held in arms facing inwards, and a standard car seat. Mean filtered EMG signal, time when muscles were active, and hip position (angles) were calculated. Compared to the Pavlik harness, infants exhibited similar adductor activity (but lower hamstring and gluteus maximus activity) in the Rhino abduction brace, similar adductor and gluteus maximus activity (but lower quadriceps and hamstring activity) in the baby carrier, similar but highly variable muscle activity in-arms, and significantly lower muscle activity in the car seat. Hip position was similar between the baby carrier and the Pavlik harness. This novel infant biomechanics study illustrates the potential benefits of using inward-facing soft-structured baby carriers for healthy hip development and highlights the potential negative impact of using supine-lying container-type devices such as car seats for prolonged periods of time. Further study is needed to understand the full picture of how body position impacts infant musculoskeletal development.
