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Positional changes of the frontoparietal ossification centers in perinatal craniosynostotic rabbits
J J Dechant1, M P Mooney, G M Cooper
1Department of Anthropology, School of Nursing, University of Pittsburgh, PA 15261, USA.
Insights
Craniosynostosis is not caused by early bony tuber displacement. In rabbits, frontoparietal bone displacement occurs after coronal suture fusion, suggesting it is a secondary change, not a primary cause.
Area of Science:
- Developmental biology
- Craniofacial development
- Skeletal biology
Background:
- Craniosynostosis (CS) is a skull malformation often attributed to premature fusion of cranial sutures.
- A leading hypothesis suggests abnormally located ossification centers (bony tubers) precede suture fusion in CS.
- This study investigates the timing of ossification center displacement relative to suture fusion in a rabbit model.
Purpose of the Study:
- To test the hypothesis that abnormal ossification center location causes craniosynostosis.
- To determine if bony tuber displacement precedes or follows coronal suture fusion in a rabbit model.
- To differentiate primary versus secondary causes of ossification center abnormalities in familial nonsyndromic CS.
Main Methods:
- Utilized 99 New Zealand White rabbit calvariae (23-34 days postconception).
- Compared normal controls, delayed-onset CS, and bilateral/unilateral CS groups.
- Measured ossification center distances using microscopy and 2-D digitization, analyzed with linear regression.
Main Results:
- Frontoparietal ossification centers showed similar initial locations but diverged over time in synostosed versus normal rabbits.
- Normal and delayed-onset ossification centers increased in distance more rapidly than in synostosed rabbits.
- Interfrontal and interparietal ossification center distances showed no significant differences among groups.
Conclusions:
- Frontoparietal ossification center displacement in synostosed rabbits occurs after suture fusion, not before.
- Bony tuber displacement is likely a secondary, compensatory change following craniosynostosis.
- Findings challenge the hypothesis that initial ossification center malposition is the primary cause of CS.
Abstract:
It has been suggested that craniosynostosis is caused by abnormally located ossification centers (i.e., bony tubers) in the developing skull prior to suture formation [Mathijssen et al., 1996, 1997]. The present study was designed to test this hypothesis in a rabbit model of human familial, nonsyndromic coronal suture (CS) synostosis. Calvariae were taken from 99 New Zealand White rabbit perinates (55 normal controls, 15 with delayed-onset CS synostosis, and 29 with bilateral or unilateral CS synostosis), ranging in age from 23 to 34 days postconception (synostosis occurs at approximately 23 days in this model). Frontoparietal, interfrontal, and interparietal ossification center distances were obtained using a Wild microscope with camera lucida attachment and a 2-D computer digitization technique. Linear regression analysis was used to compare age-related changes in the perinatal ossification centers among groups. Results revealed that frontoparietal ossification center regression line slopes had similar start points (24-day intercepts) with significantly (P < 0.05) diverging slopes over time. Normal and delayed-onset ossification center distance increased more rapidly than in synostosed perinates. No significant (P > 0.05) differences were noted in regression line slopes among groups for interparietal or interfrontal ossification center distances. Results demonstrated that, in synostosed perinates, frontoparietal ossification center location was similar to normals around the time of synostosis and became displaced later. These findings suggest that ossification center (i.e., bony tuber) displacement seen in infants with craniosynostosis is probably a secondary and compensatory, postsynostotic change and not a primary causal factor of synostosis in this rabbit model.