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Femoral growth lines: bony birthmarks in infants
R L Teele1, G D Abbott, N Mogridge
1Department of Radiology, Christchurch Hospital and Christchurch School of Medicine, University of Otago, New Zealand.
Insights
A common finding in healthy infants, proximal femur growth lines appear in 39% of newborns. These lines correlate with infant age and may indicate prenatal or postnatal stress events.
Area of Science:
- Pediatric radiology
- Skeletal development
- Infant imaging
Background:
- Growth lines in the proximal femur were incidentally observed in infants undergoing antenatal renal dilatation studies.
- The prevalence and characteristics of these growth lines in healthy infants were not well-established.
Purpose of the Study:
- To determine the prevalence of proximal femur growth lines in healthy infants.
- To investigate the correlation between growth line characteristics and infant age.
- To explore potential associations between delivery mode and growth line presence.
Main Methods:
- Retrospective review of 791 voiding cystourethrograms in infants aged 0-6 months.
- Exclusion of infants with severe illness or inadequate proximal femur views, yielding a cohort of 633 healthy infants.
- Radiographic assessment for presence and distance of proximal femur growth lines from the metaphyseal edge, with data collection on delivery mode for a subset.
Main Results:
- A discernible growth line was present in 247 (39%) of the 633 eligible infants.
- A significant positive correlation was found between the distance of the growth line from the metaphysis and infant age (r = .81, p < .01).
- Infants delivered vaginally showed a higher likelihood of having a growth line compared to those born via cesarean delivery (p = .049).
Conclusions:
- Proximal femur growth lines are a common radiographic finding in healthy infants.
- The longitudinal growth rate of the proximal femoral metaphysis can be estimated from radiographs at approximately 1 mm per 11 days (1 mm per 13 days corrected for magnification).
- These growth lines may offer insights into the timing of prenatal and postnatal stressful events impacting skeletal development.
Objective:
During a study of infants who were being examined for antenatal renal dilatation, we noted that many had growth lines in their proximal femur on postnatal radiographs. We decided to determine the prevalence of growth lines in healthy infants.
Materials And Methods:
Voiding cystourethrograms of 791 neonates and infants, 0-6 months old, were reviewed. All who had documented severe illness or no reasonable view of the proximal femur were excluded, resulting in a cohort of 633 healthy infants. Each study was coded for presence or absence of a growth line in the proximal femur, and the distance of the growth line from the metaphyseal edge was measured to the nearest 0.5 mm. Radiographs were obtained on a unit with fixed tube-film distance. Data on the mode of delivery were collected for 136 infants.
Results:
Of 633 eligible infants, 247 (39%) of 633 had a discernible growth line. The distance of the growth line from the metaphysis, in millimeters, correlated significantly with age in days (r = .81, p < .01). Infants delivered vaginally were more likely to have a growth line than were those born by cesarean delivery (p = .049).
Conclusion:
A growth line in the proximal femur is common in healthy infants. The rate of longitudinal growth of the proximal femoral metaphysis, on radiographs, is approximately 1 mm per 11 days (1 mm per 13 days when corrected for magnification). Approximation of the timing of prenatal and postnatal stressful events that result in a growth disturbance line may be possible.
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