Exploring infant hip position and muscle activity in common baby gear and orthopedic devices

Mechanical environment influences muscle activity during infant rolling

An infant's musculoskeletal and motor development is largely affected by their environment. Understanding how different mechanical environments affect an infant's movements and muscle use is necessary to inform the juvenile products industry and reduce incidents involving inclined nursery products each year. The purpose of this study was to determine how the coordinated movements and corresponding muscle activation patterns are affected by different mechanical environments, specifically the back incline angle. Thirty-eight healthy infants (age: 6.5 ± 0.7 months; 23 M/15 F) were enrolled in this IRB-approved in-vivo biomechanics study. Surface electromyography sensors recorded muscle activity of the erector spinae, abdominal muscles, quadriceps, and hamstrings while infants rolled in five different mechanical environments: a flat surface and four device configurations representing a range of inclines infants are commonly exposed to. Coordinated movements were determined using video. In all configurations featuring an inclined seatback angle, infants experienced significantly higher erector spinae muscle activation and significantly lower abdominal muscle activation compared to the flat surface. Infants also exhibited a different coordinated movement featuring spinal extension and a pelvic thrust in the inclined device configurations that was not previously observed on the flat surface alone. Understanding how infants coordinate their movements and use their muscles during rolling in different inclined environments provides more insight into motor development and may inform the juvenile products industry. Many factors impact an infant's movements, therefore future work should explore how other environmental interactions influence an infant's movements and muscle activation, particularly for rolling.

Effect of the Pavlik harness used in the treatment of developmental dysplasia of the hip on unaided sitting and independent walking age

Background

Pavlik harness is the most widely used orthosis in the treatment of developmental dysplasia of the hip. The aim of this study was to evaluate the effect of the Pavlik harness on the development of "unaided sitting" and "independent walking" in infants with developmental dysplasia of the hip.

Methods

This prospective study, conducted from 2017 to 2020, included infants undergoing Pavlik harness therapy. Inclusion criteria comprised gestational age > 37 weeks, treatment initiation before 6 months of age, and no prior treatment for developmental dysplasia of the hip. We assessed treatment initiation age, treatment duration, and the age of achieving unaided sitting and independent walking.

Results

In the patient group, unaided sitting commenced at a mean age of 6.8 ± 1.6 (range: 4-11) months, while independent walking began at a mean age of 12.7 ± 1.8 (range: 9-18) months. By 15 months, 92% of the patients achieved independent walking. In the control group, unaided sitting occurred at a mean age of 6.1 ± 1.1 (range: 4-8) months, and independent walking at 11.8 ± 1.6 (range: 9-18) months. A significant positive correlation was observed between the duration of Pavlik harness usage and the age of unaided sitting (p < 0.001) and independent walking (p < 0.001).

Conclusion

Our study indicates that Pavlik harness treatment for developmental dysplasia of the hip is generally safe and does not lead to clinically significant delays in unaided sitting and independent walking. However, some minor delays may occur due to extended orthosis use.

Level of evidence

level III-prospective cohort study.

Muscle activation and coordinated movements of infant rolling

Rolling is a critical step of infant development, encouraging muscle coordination and enabling independent exploration. Understanding muscle activity during infant rolling movements on a flat surface is necessary to more fully characterize how the rolling milestone is achieved. The purpose of this study was to determine infants' muscle activation throughout roll initiation for six previously established coordinated movements. Thirty-eight healthy infants (age: 6.5 ± 0.7 months; 23M/15F) were enrolled in this IRB-approved in-vivo biomechanics study. Surface electromyography sensors recorded muscle utilization from the erector spinae, abdominal muscles, quadriceps, and hamstrings while infants rolled. Each rolling movement was categorized as one of six roll types, and the mean muscle activity was analyzed. All roll types required initial activation of all measured muscle groups. Movements featuring axial rotation of the torso relative to the pelvis required highly active erector spinae muscles. Movements featuring trunk and hip flexion required highly active abdominal muscles. Infants used distinct coordinated muscle activations to achieve the six different roll types on a flat surface. A foundational understanding of the different muscle activation patterns required during infant rolling will provide crucial insight into motor development. This study quantified muscle coordination required of infants to achieve rolling on a firm flat surface. Previous research indicates that the mechanical environment in which an infant is placed impacts muscle activity and body position during normal lying. Therefore, future work should explore if mechanical environments that differ from a flat and firm surface also influence these coordinated movements and muscle activations.

Developmental Dysplasia of the Hip - Part 1

Developmental dysplasia of the hip (DDH) is a condition characterized by changes in joint formation within the last months of intrauterine life or the first months after birth. Developmental dysplasia of the hip presentation ranges from femoroacetabular instability to several stages of dysplasia up to complete dislocation. Early diagnosis is essential for successful treatment. Clinical screening, including appropriate maneuvers, is critical in newborns and subsequent examinations during the growth of the child. Infants with suspected DDH must undergo an ultrasound screening, especially those with a breech presentation at delivery or a family history of the condition. A hip ultrasound within the first months, followed by pelvic radiograph at 4 or 6 months, determines the diagnosis and helps follow-up. Treatment consists of concentric reduction and hip maintenance and stabilization with joint remodeling. The initial choices are flexion/abduction orthoses; older children may require a spica cast after closed reduction, with or without tenotomy. An open reduction also can be indicated. After 18 months, the choices include pelvic osteotomies with capsuloplasty and, eventually, acetabular and femoral osteotomies. The follow-up of treated children must continue throughout their growth due to the potential risk of late dysplasia.

Ultrasonographic evaluation of infant hips in the Pavlik harness compared to body-worn commercial baby carriers

While many factors contribute to development and subsequent correction of developmental hip dysplasia (DDH) in infants, hip positioning and muscle activity play a significant role. Lower-limb restrictive extension positions, such as with swaddling, are detrimental for hip development, and some baby gear leads to reduced lower limb muscle activity. Yet how baby gear impacts hip position during wear remains unclear. The purpose of this study was to compare the Graf's alpha angle and femoral head coverage of healthy infants and infants with mild DDH (instability) in the Pavlik harness and baby carriers. We obtained coronal hip ultrasound images of 10 healthy full-term infants (13.5 ± 3.4 weeks, 5F/5M) and three full-term mild DDH infants (8.9 ± 4.0 weeks, 2F/1M) in three conditions: Pavlik harness, wide-base baby carrier, and narrow-base baby carrier. Repeated measures analysis of variance was used to compare Graf's alpha angles and femoral head coverages across the conditions (p < 0.05), with post hoc pairwise tests (p < 0.0167). The Graf's alpha angle in the narrow-base carrier was 6.9° lower than the Pavlik harness, while the wide-base carrier was not different. Femoral head coverage was 10%-12% lower for the narrow-base carrier. The three mild DDH infants exhibited lower Graf's alpha angles and femoral head coverage in all measurements, with the Graf's alpha angle in the narrow-base carrier measuring 49.0°. This research demonstrated that wide-base baby carriers held hips in a position that was not significantly different from the Pavlik harness, meaning that babywearing in a wide-base carrier may have benefits for healthy hip development.

Challenges in Kinetic-Kinematic Driven Musculoskeletal Subject-Specific Infant Modeling

Musculoskeletal computational models provide a non-invasive approach to investigate human movement biomechanics. These models could be particularly useful for pediatric applications where in vivo and in vitro biomechanical parameters are difficult or impossible to examine using physical experiments alone. The objective was to develop a novel musculoskeletal subject-specific infant model to investigate hip joint biomechanics during cyclic leg movements. Experimental motion-capture marker data of a supine-lying 2-month-old infant were placed on a generic GAIT 2392 OpenSim model. After scaling the model using body segment anthropometric measurements and joint center locations, inverse kinematics and dynamics were used to estimate hip ranges of motion and moments. For the left hip, a maximum moment of 0.975 Nm and a minimum joint moment of 0.031 Nm were estimated at 34.6° and 65.5° of flexion, respectively. For the right hip, a maximum moment of 0.906 Nm and a minimum joint moment of 0.265 Nm were estimated at 23.4° and 66.5° of flexion, respectively. Results showed agreement with reported values from the literature. Further model refinements and validations are needed to develop and establish a normative infant dataset, which will be particularly important when investigating the movement of infants with pathologies such as developmental dysplasia of the hip. This research represents the first step in the longitudinal development of a model that will critically contribute to our understanding of infant growth and development during the first year of life.

Developmental Dysplasia of Hip and Post-natal Positioning: Role of Swaddling and Baby-Wearing

INTRODUCTION

Traditional swaddling, which implies restrictive immobilisation of the infant's lower limbs with the hips in forced extension and adduction, has been shown to be a risk factor for Developmental Dysplasia of Hip (DDH).

METHODS

We reviewed the literature regarding the correlation between DDH and post-natal positioning by swaddling and baby-wearing, to draw awareness of healthcare professionals towards an important risk factor for DDH that has often been overlooked.

RESULTS

There is overwhelming evidence in the literature, by both experimental and clinical studies, that proves the close association between improper post-natal positioning of the baby's hips in extension-adduction and an increased incidence of DDH. On the other hand, "hip safe" swaddling which allows unrestricted flexion-abduction movements of the infants' hips, and the use of baby-wearing devices which keep the lower limbs in an attitude of hip flexion-abduction and knee flexion, is optimal for hip development. Populations which practice these "hip-safe" techniques of infant immobilisation have a lower incidence of DDH as compared to those which practice restrictive immobilisation. Furthermore, populations which have adopted "hip-safe" positioning have demonstrated a significant decrease in the incidence of DDH. Understanding this association is vital, since this is a modifiable risk factor, rectification of which can decrease the incidence of DDH.

CONCLUSION

Policy makers and governments must design educational campaigns tailored to their respective populations to increase awareness regarding the benefits of "hip-safe" techniques of infant positioning, since this simple intervention has the potential of decreasing the incidence of DDH.

Do inclined sleeping surfaces impact infants' muscle activity and movement? A safe sleep product design perspective

The design of inclined sleep products may be associated with an increased risk of suffocation when an infant finds themselves prone in the product. It is important to understand how different inclined sleep surface angles impact infants' muscle activity when considering a safe sleep environment. The purpose of this study was to assess muscle activity of healthy infants when they lie supine and prone on different inclined crib mattress surfaces (0° vs. 10° vs. 20°). Fifteen healthy infants were recruited for this study. Surface EMG was recorded from cervical paraspinal, abdominal, lumbar erector spinae, and triceps muscles for 60 s during supine and prone positioning. Repeated measures ANOVAs and Bonferroni post-hoc adjustments were performed to test the effect of incline angles. Paired t-tests were performed to test the effect of position (supine vs. prone). During prone lying, abdominal muscle activity increased by 33% and 71% for 10° and 20° compared to 0°, while erector spinae and triceps muscle activity decreased for 20° compared to 0°. Lumbar erector spinae and cervical paraspinal muscle activity increased by 185% and 283% for prone compared to supine lying. During prone positioning, the 20° inclined surface resulted in significantly higher muscle activity of the trunk core muscles (abdominals), which may exacerbate fatigue and contribute to suffocation if an infant cannot self-correct to the supine position. Compared to supine positioning, prone lying requires higher musculoskeletal effort to maintain a safe posture to prevent suffocation, and babies likely fatigue faster when lying prone.