The effects of mechanical immobilization on sutural development in the growing rabbit

Comparative digital reconstruction of Pica pica and Struthio camelus and their cranial suture ontogenies

To date, several studies describe post-hatching ontogenetic variation in birds; however, none of these studies document and compare ontogenetic variation of the entire skull in multiple avian species. Therefore, we studied ontogenetic skull variation of two bird species with very different ecologies, Pica pica, and Struthio camelus, using μCT based 3D reconstructions. For each specimen, we performed bone-by-bone segmentation in order to visualize and describe the morphological variation of each bone during ontogeny and estimated the average sutural closure of the skulls to identify different ontogenetic stages. Although bone fusion of P. pica occurs more rapidly than that of S. camelus the general sequence of bone fusion follows a similar trend from posterior to anterior, but a more detailed analysis reveals some interspecific variation in the fusion patterns. Although growth persists over a longer period in S. camelus than in P. pica and adults of the former species are significantly larger, the skull of the most mature S. camelus is still less fused than that of P. pica. Different growth and fusion patterns of the two species indicate that the interspecific ontogenetic variation could be related to heterochronic developments. Nevertheless, this hypothesis needs to be tested in a broader phylogenetic framework in order to detect the evolutionary direction of the potential heterochronic transformations.

Changes in biomechanical strain and morphology of rat calvarial sutures and bone after Tgf-β3 inhibition of posterior interfrontal suture fusion

Craniofacial sutures are bone growth fronts that respond and adapt to biomechanical environments. Little is known of the role sutures play in regulating the skull biomechanical environment during patency and fusion conditions, especially how delayed or premature suture fusion will impact skull biomechanics. Tgf-β3 has been shown to prevent or delay suture fusion over the short term in rat skulls, yet the long-term patency or its consequences in treated sutures is not known. It was therefore hypothesized that Tgf-β3 had a long-term impact to prevent suture fusion and thus alter the skull biomechanics. In this study, collagen gels containing 3 ng Tgf-β3 were surgically placed superficial to the posterior interfrontal suture (IFS) and deep to the periosteum in postnatal day 9 (P9) rats. At P9, P24, and P70, biting forces and strains over left parietal bone, posterior IFS, and sagittal suture were measured with masticatory muscles bilaterally stimulated, after which the rats were sacrificed and suture patency analyzed histologically. Results demonstrated that Tgf-β3 treated sutures showed less fusion over time than control groups, and strain patterns in the skulls of the Tgf-β3-treated group were different from that of the control group. Although bite force increased with age, no alterations in bite force were attributable to Tgf-β3 treatment. These findings suggest that the continued presence of patent sutures can affect strain patterns, perhaps when higher bite forces are present as in adult animals.

NEW WORLD CRANIAL DEFORMATION PRACTICES

INTRODUCTION

Throughout history, prehistoric and even some contemporary civilizations have practiced various forms of intentional and unintentional cranial deformation. Plagiocephaly can be the result of craniosynostosis, infant positioning, or other unintentional or intentional deformation.

MATERIALS

We reviewed the medical and anthropological literature and the anthropological collections of Arizona State University and the San Diego Museum of Man for evidence of cranial deformation and its possible physiological and cognitive side effects. Evidence of cranial shaping was also sought among art or stone work from representative cultures.

RESULTS

The anthropological record and literature attest to the presence of much more severe forms of deformation than that seen as a result of contemporary infant positioning. Despite this evidence, there is no anthropological evidence as to the possible cognitive effects that such deformation may have, although some evidence is reviewed that suggests a possible physiological mechanism for the same.

CONCLUSION

Because we can only view these cultures through the relics of time, any conclusions one might draw from the anthropological and historical record regarding the cognitive effects of head deformation can only be inferred through generalized observations and are tenuous. Nevertheless, there does not seem to be any evidence of negative effect on the societies that have practiced even very severe forms of intentional cranial deformation (e.g., the Olmec and Maya). On the other hand, the physical anthropology and the contemporary developmental literature suggest possible mechanisms for such an effect.

Biomechanical Strain and Morphologic Changes with Age in Rat Calvarial Bone and Sutures

BACKGROUND

The role of calvarial sutures in transmitting biomechanical forces within the head is unclear.

METHODS

To examine the biomechanical characteristics of sutures, the authors measured bite force changes in rats and tested for alterations in strain across intrafrontal and sagittal sutures and within parietal bone with age. To understand the effects of suture fusion on strain distribution in the head, the authors measured percentage fusion of the intrafrontal sutures with age (n = 6 per age group). The masticatory muscles in anesthetized 9-, 24-, and 70-day-old rats (n = 15 per group) were bilaterally stimulated. Stacked delta rosette gauges were fixed across the intrafrontal sutures and sagittal suture, or on the parietal bone. Strain and bite force were measured with a bite force transducer positioned at the incisors.

RESULTS

Bite force increased significantly (p < 0.05) with age (9-day-old rats, 72.6 +/- 20 gf; 24-day-old rats, 707.3 +/- 150 gf; 70-day-old rats, 2425.6 +/- 255 gf). Some significant differences were found between the volume and direction of strain among sites and age groups. Compressive strains of 230 microepsilon on average were found across the intrafrontal sutures at all ages. In contrast, tensile strains less than 180 microepsilon on average were found across the sagittal sutures of 9- and 24-day-old rats, increasing to 940 microepsilon on average at day 70. Tensile strains in parietal bone tended to be less than 150 microepsilon.

CONCLUSIONS

The timing of sutural closure and patterns of transsutural strain do not suggest that strain patterns contribute to initial fusion in the intrafrontal sutures. Differences in strain are likely related to changes in rat skull kinetics with growth, perhaps resulting from fusion of the intrafrontal sutures.

Cellular response to force application at craniofacial sutures

OBJECTIVES

To provide a comprehensive review of the literature describing research done on the responses of suture cells to force application in vitro and in vivo.

DESIGN AND RESULTS

This review outlines the types of forces that can be applied, methods of applying the forces, the sutures used in experiments, and the changes in morphology, molecular biology (gene and protein expression), and cell biology (proliferation, differentiation, apoptosis) in response to these forces.

CONCLUSION

The molecular response of sutures to force needs to be further investigated as these molecules can be used to enhance the way in which craniofacial sutures respond to mechanical force during orthopedic-orthodontic treatment.

The extracellular matrix environment in suture morphogenesis and growth

Sutures are the major bone growth sites of the craniofacial skeleton and form in response to developmental approximation of and interaction between two opposing osteogenic fronts. Premature obliteration of these craniofacial bone growth sites or craniosynostosis results in compensatory growth at other bone growth sites, with concomitant craniofacial dysmorphology. While much is now known about the growth and transcriptional factor regulation of suture formation and maintenance, little about the nature of the extracellular environment within sutures and their surrounding bones has been described. This review elucidates the nature of the sutural extracellular matrix and its role in mediating suture maintenance and growth through the regulation of cellular and biomechanical signaling.

Unicoronal Suture Immobilization in the Fetal Rabbit

Pre-clinical evaluation of surgical procedures aimed to correct craniosynostosis is ideally performed in species of small animals characterized by perinatal brain development, early skeletal maturation, and genuine synostosis in all newborns. It would be nearly impossible to breed such a colony to homozygosity, so most researchers have resorted to artificial postnatal suture immobilization. Our aim was to test the hypothesis that artificial immobilization of a unicoronal suture in the fetal rabbit (25 days of gestation) would result in neurocranial growth alterations similar to those seen in the 9-day postnatally immobilized or congenital synostotic rabbit models. The advantages of prenatal immobilization are that rabbits can undergo the tested corrective procedure at postnatal day 9. This age corresponds to a human age of 6 months and allows the deformity and the effects of its correction to be more readily detected. The heads of 25-day-old fetuses of five time-dated pregnant New Zealand white rabbits were exposed by hysterotomy. The left unicoronal suture of 4 fetuses in each litter was immobilized with a polyglactin suture piercing the frontal and parietal bone plates. The remaining two fetuses were sham-operated. Nine days after spontaneous delivery, all rabbits were marked with four titanium screws close to the sagittal and coronal sutures. Growth was recorded with dorsoventral cephalograms at 9 and 90 days. The group with the immobilized suture showed a small increase in growth across the sagittal sutures. However, the decreases in growth at the unicoronal suture in both the immobilized (5.41-mm difference with sham-treated group) and nonimmobilized (1.17-mm difference with sham-treated group) were significant. Fetal immobilization results in growth alterations similar to those observed after postnatal immobilization.

Craniofacial sutures: morphology, growth, and in vivo masticatory strains

The growth and morphology of craniofacial sutures are thought to reflect their functional environment. However, little is known about in vivo sutural mechanics. The present study investigates the strains experienced by the internasal, nasofrontal, and anterior interfrontal sutures during masticatory activity in 4-6-month-old miniature swine (Sus scrofa). Measurements of the bony/fibrous arrangements and growth rates of these sutures were then examined in the context of their mechanical environment. Large tensile strains were measured in the interfrontal suture (1,036 microepsilon +/- 400 SD), whereas the posterior internasal suture was under moderate compression (-440 microepsilon +/- 238) and the nasofrontal suture experienced large compression (-1,583 microepsilon +/- 506). Sutural interdigitation was associated with compressive strain. The collagen fibers of the internasal and interfrontal sutures were clearly arranged to resist compression and tension, respectively, whereas those of the nasofrontal suture could not be readily characterized as either compression or tension resisting. The average linear rate of growth over a 1-week period at the nasofrontal suture (133.8 micrometer, +/- 50.9 S.D) was significantly greater than that of both the internasal and interfrontal sutures (39.2 micrometer +/- 11.4 and 65. 5 micrometer +/- 14.0, respectively). Histological observations suggest that the nasofrontal suture contains chondroid tissue, which may explain the unexpected combination of high compressive loading and rapid growth in this suture.

Palatal thickening and facial form in Paranthropus: examination of alternative developmental models

Paranthropus is distinctive among hominoids in its possession of a greatly thickened hard palate. Although traditionally considered a structural adaptation to counter high-magnitude masticatory stress, alternative developmental models are equally viable. Three models of palatal thickening were evaluated in this study. A mechanical model interprets palatal thickening as a compensatory response to increased instability of the midpalatal suture effected by an anterior placement of the masseteric muscle mass. This model predicts that palatal thickness is correlated with the length of the palate posterior to the masseteric tubercle. Two non-mechanical models consider the thickness of the hard palate to be structurally related to and therefore correlated with either 1) the degree to which the premaxilla overlaps the hard palate in the subnasal region or 2) the height of the posterior facial skeleton. The correlation of craniofacial variables was assessed intraspecifically in ontogenetic series of great ape and human crania. Tests of correlation were performed for each comparison using both residuals calculated from reduced major axis regression of the variable of interest against a measure of cranial size and shape ratios. A significant correlation of palatal thickness with posterior facial height in Pan suggests that the unusually thick hard palate of Paranthropus is directly related to the increased posterior facial height characteristic of this taxon. Further evaluation suggests that extreme palatal thickening in these specimens occurred by virtue of their possession of a nasal septum morphology in which the vomer extends onto the superior and nasal surface of the premaxilla. Such a morphology would have constrained the palatal nasal lamina to maintain the approximate level of the premaxillary nasal lamina throughout the growth process thereby promoting palatal thickening.

Failure of onlay bone grafts to integrate over the calvarial suture: observations in adult isogeneic rats

Bone grafting constitutes an important tool in cranio-maxillofacial skeletal reconstruction and augmentation. Much effort has been directed to improve graft survival and volumetric maintenance. The effects of the sutural tissue proper on graft incorporation has not yet been explored. The purpose of this report was to analyze the effects of positioning an onlay graft over a non-growing sutural region. Twelve adult rats received femoral or tibial uni- or bicortical grafts placed over the temporal suture. The findings were assessed by routine microscopy and immunohistochemistry after 4, 12, and 20 weeks. The sutural tissue expanded between the graft and the host bed in an umbrella-like pattern, which locally inhibited graft incorporation. Of the tested cartilage and bone proteins and proteoglycans, labelling was distinct only for osteopontin and fibromodulin, indicating a moderate remodelling activity in the area. The importance and consequences of the findings are discussed.

The role of sutures in normal and abnormal craniofacial growth

The paper is a shortened version of a paper read at the symposium on craniofacial growth, in which the literature on various aspects of sutures was reviewed. Suture development, structure, growth, and closure are covered, and the response of sutures to orthopedic forces and their role in craniosynostosis exemplified. Rather than being an extensive review, references are included preferably to present diversity in results and methods within the subtitle of the symposium, 'mechanisms and study methods'.

Development of a strain of rabbits with congenital simple nonsyndromic coronal suture synostosis. Part I: Breeding demographics, inheritance pattern, and craniofacial anomalies

The lack of an animal model of congenital coronal suture (CS) synostosis has prompted the widespread use of an experimental rabbit model using adhesive immobilization of the CS. Such postnatal models have helped make significant scientific contributions but may still not fully represent all aspects of the human congenital condition. In the March 1993 issue of The Cleft Palate-Craniofacial Journal we reported a female rabbit born in our laboratory with complete bilateral CS synostosis. This follow-up study presents our attempts to breed this animal and establish a strain of craniosynostotic rabbits. To date, we have accomplished 10 back- and intercrosses with these animals and have produced a total of 71 live offspring; 10 animals exhibited complete nonsyndromic unilateral (plagiocephalic) or bilateral (brachycephalic) CS synostotic deformities at birth, and 19 animals exhibited partial CS synostosis that showed more than 75% growth retardation across the CS (well below the 95% confidence interval for normals). Results revealed that gestational time and litter size averages were consistent with those reported for the strain, although the average litter size decreased with increased inbreeding. By 1.5 weeks of age the completely synostosed animals already exhibited brachycephalic cranial vaults and midfacial hypoplasia compared to unaffected siblings. Initial pedigree analysis suggested an autosomal dominant inheritance pattern with incomplete penetrance and variable expressivity. The development of such a congenital rabbit model may prove useful in helping to understand the etiopathogenesis of this condition in human populations.

Development of a strain of rabbits with congenital simple nonsyndromic coronal suture synostosis. Part II: Somatic and craniofacial growth patterns

In the March 1993 issue of The Cleft Palate-Craniofacial Journal we reported a female rabbit born in our laboratory with complete bilateral coronal suture (CS) synostosis. This follow-up study presents our attempts to breed the animal and establish a strain of craniosynostotic rabbits. The second part of this study presents longitudinal somatic and craniofacial growth data in offspring with coronal suture synostosis. Serial growth data from 72 animals were collected for the present study. The sample consisted of 11 animals (10 offspring and the original female) with complete nonsyndromic unilateral (plagiocephalic) or bilateral (brachycephalic) CS synostosis, 19 animals with partial CS synostosis, and 42 unaffected control litter mates. At 10 days of age, all animals had radiopaque amalgam markers placed on either side of the frontonasal, coronal, anterior lambdoidal, and sagittal sutures. Body weights and serial lateral and dorsoventral head radiographs were taken at 1.5 (10 days), 6, 12, and 18 weeks of age. All animals showed similar body weights at 1.5 weeks of age, while completely synostosed animals exhibited a slight (about 12%), but significantly (p < .001) lowered body weight by 18 weeks of age. Results revealed that by 1.5 weeks of age the completely synostosed animals already exhibited brachycephalic cranial vaults, midfacial hypoplasia, and increased flattening of the cranial base compared to unaffected siblings. This pattern continued through 18 weeks of age, with the partially synostosed animals exhibiting intermediate morphologies.(ABSTRACT TRUNCATED AT 250 WORDS)

Sutural biology and the correlates of craniosynostosis

The purpose of this paper is to provide a new perspective on craniosynostosis by correlating what is known about sutural biology with the events of craniosynostosis per se. A number of key points emerge from this analysis: 1) Sutural initiation may take place by overlapping, which results in beveled sutures, or by end-to-end approximation, which produces nonbeveled, end-to-end sutures. All end-to-end sutures occur in the midline (e.g., sagittal and metopic) probably because embryonic biomechanical forces on either side of the initiating suture tend to be equal in magnitude. A correlate appears to be that only synostosed sutures of the midline have pronounced bony ridging. 2) Long-term histologic observations of the sutural life cycle call into question the number of layers within sutures. The structure varies not only in different sutures, but also within the same suture over time. 3) Few, if any, of the many elegant experimental research studies in the field of sutural biology have increased our understanding of craniosynostosis per se. An understanding of the pathogenesis of craniosynostosis requires a genetic animal model with primary craniosynostosis and molecular techniques to understand the gene defect. This may allow insight into pathogenetic mechanisms involved in primary craniosynostosis. It may prove to be quite heterogeneous at the basic level. 4) The relationship between suture closure, cessation of growth, and functional demands across sutures poses questions about various biological relationships. Two conclusions are provocative. First, cessation of growth does not necessarily, or always lead to fusion of sutures. Second, although patent sutures aid in the growth process, some growth can take place after suture closure. 5) In an affected suture, craniosynostosis usually begins at a single point and then spreads along the suture. This has been shown by serial sectioning and calls into question results of studies in which the affected sutures are only histologically sampled. 6) Craniosynostosis is etiologically and pathogenetically heterogeneous. Known human causes are reviewed. Is craniosynostosis simply normal suture closure commencing too early?(ABSTRACT TRUNCATED AT 400 WORDS)

Congenital bilateral coronal suture synostosis in a rabbit and craniofacial growth comparisons with experimental models

Experimental rabbit models of postnatal coronal suture (CS) synostosis have helped make significant contributions towards the understanding and surgical management of human congenital craniosynostosis. The present study compares craniofacial growth patterns in animals with experimental CS immobilization and in a rabbit born in our laboratory with congenital CS synostosis. The study sample consisted of 10 sham controls, 14 experimental animals with bilateral CS immobilization, and one animal with congenital, bilateral CS synostosis. At 1.5 weeks of age, all animals had amalgam markers placed on either side of the frontonasal, coronal, and anterior lambdoid sutures. At this time, the experimental animals had bilateral CS immobilization using methyl-methacrylate. Serial lateral head x-rays were taken at 1.5, 6, 12, and 18 weeks of age. Results revealed that by 1.5 weeks of age the congenital animal already exhibited changes in the cranial vault, cranial base, midface, and orthocephalic cranial base angles compared to controls. By 6 weeks of age, animals with experimental immobilization showed compensatory growth patterns similar to the congenital animal, particularly at the calvarial sutures and upper midface. This pattern continued through 18 weeks. Results showed that experimental, postnatal CS immobilization produced similar craniofacial growth patterns to those observed for our single congenital animal, but to a lesser degree, and therefore validates, in part, findings from experimental rabbit models of synostosis.

A new method for the creation and measurement of experimental craniosynostosis

Craniosynostosis is described as a condition in which the premature closure of one or more cranial sutures is exposed as a skull deformity alone or accompanied by neurological disturbances. According to previous research it seemed possible to create an experimental model for investigating the disease by simply resecting a suture in a newborn rabbit. We resected 16 coronal sutures in 16 newborn rabbits and had the skulls investigated for shape and histology up to 6 months of age. A clear deformity at the cranial vault could be detected. The fused site of the suturectomy later on presented a suture-like structure which was macroscopically distinct from a normal skull suture. The procedure is thus established, first, for investigating procedures for treating craniosynostosis in the growing skull, and, secondly, for studying the pathophysiology of craniosynostosis.

Effects of unilateral premature fusion of the zygomaxillary suture on the growth of nasomaxillary complex

Unilateral premature fusion of the zygomaxillary suture was produced in 2-week-old guinea pigs by immobilization with methyl-cyanoacrylate adhesive. The effects of sutural fusion on the growth of the nasomaxillary complex were evaluated by radiographic cephalometry with implants, and histologic assessment. The immobilization successfully constrained the anteroinferior displacement of the maxilla and zygomatic bone on the fused side. Compensatory responsive remodeling at adjacent sutures and in certain regions of the nasomaxillary complex was observed. Developmental asymmetry was found when the fused side was compared with the nonfused side. No gross anatomic asymmetry of the facial complex as a whole, however, was detected. Adaptive compensation involving periosteal bone deposition occurred at the junction of the lower maxillary process and the maxilla proper on the fused side. This, together with periosteal bone resorption in corresponding areas on the nonfused side served to offset any developmental asymmetry that might have occurred, thus leading to a compensatory preclusion of gross anatomic asymmetry.

Craniosynostosis update 1987

Information on craniosynostosis in this paper updates "Craniosynostosis: Diagnosis, Evaluation, and Management" (Cohen MM Jr: New York: Raven Press, 1986). It also discusses recent developments that were included in the book but need further explanation or emphasis. Subjects discussed are: epidemiology, etiology, sutural biology, growth and development, neurological and psychosocial aspects, surgery, cloverleaf skulls, craniosynostosis syndromes, and prenatal diagnosis. Under the subject of etiology, fetal head constraint, maternal thyroid disease, calcified cephalohematoma, teratogens, and delayed suture closure and Wormian bones are considered. An updating of 15 cloverleaf skull conditions includes four monogenic disorders, two chromosomal disorders, one disruption, one iatrogenic condition, and seven syndromes of unknown cause. Newly recognized disorders with cloverleaf skull include Beare-Stevenson cutis gyratum syndrome and Say-Poznanski syndrome. Craniosynostosis syndromes and associations discussed include acrocraniofacial dysostosis, Apert syndrome, Beare-Stevenson cutis gyratum syndrome, Calabro syndrome, calvarial hyperostosis, chromosomal craniostenosis, Cole-Carpenter type osteogenesis imperfecta, Crouzon syndrome, Curry-Jones syndrome, Curry variant of Carpenter syndrome, cutis aplasia and cranial stenosis, Fontaine-Farriaux syndrome, Gomex-López-Hernández syndrome, Hersh syndrome, hyper-IgE syndrome and craniostenosis, hypomandibular faciocranial dysostosis, Marfanoid features and craniostenosis, Pfeiffer-type cardiocranial syndrome, Pfeiffer-type dolichocephalosyndactyly, and Say-Barber syndrome.

Effects of bone wax on rabbit cranial bone lesions

The present study was designed to elucidate the reactions of cranial membranous bone to bone wax. In ten young rabbits, twenty parietal bone defects were created by drilling, the edges of which were partly extended using rongeur forceps to enable investigation of eventual thermal effects. Half of the marginal bone surrounding the lesions was covered by bone wax, the remainder serving as control. The animals were sacrificed 1 and 7 weeks after surgery, and block specimens prepared for light microscopy. Merely slight tissue reactions to the bone wax were discerned. Bony regeneration occurred mainly from the dura mater and the pericranium, but also from the bony rim. Reskeletalization was markedly impaired by the presence of bone wax. Heat generated by drilling caused reduced bone formation despite constant irrigation peroperatively. Clinical consequences are discussed.

Restricted growth at the frontonasal suture: alterations in craniofacial growth in rabbits

Apposition of bone at the sutural margin is generally thought to be a compensatory adjustment to growing soft-tissue organs such as the brain or eyes within the skull. The frontonasal suture which is located at the interface between the cranial and facial skeletons is a site of extremely active growth in the young rabbit. Recently, we showed that premature closure of a cranial suture, the coronal suture, can alter the growth not only at the adjacent frontonasal suture but also of the basicranium and midface. This study examines the effects of restricted growth at the frontonasal suture on both growth at adjacent cranial sutures and linear growth of the basicranium and midface. Thirty newborn New Zealand White rabbits were subdivided into experimental and sham-treated groups of equal size and distribution for sex and birth weight. At 9 days of age, the frontonasal suture of each experimental animal was immobilized by bilateral application of methyl-cyanoacrylate adhesive across the frontonasal suture. Growth and morphometric changes were monitored by radiocephalometric methods through 120 days of age by bilateral implantation of radiopague markers on each side of frontonasal, coronal, and anterior lambdoid sutures. Results indicate that restricted growth at the frontonasal suture results not only in a significant shortening of the midface but also in significant decreases in growth at the coronal and internasal sutures. Growth at the interfrontal and sagittal sutures is increased. Furthermore, growth at the anterior portion of the nasal bones is significantly increased, thereby offsetting a portion of the decreased nasal bone length resulting from frontonasal restriction.

Lambdoid synostosis. Part 1. The lambdoid suture: normal development and pathology of "synostosis"

The microscopic development of the normal lambdoid suture was studied in autopsy specimens from 19 normal subjects ranging in age from 20 weeks' gestation to 60 years. The cellular activity at the suture varied considerably with age; however, maximal activity was seen in specimens approximately 3 months of age. There were several unusual features, including a high incidence of cartilaginous differentiation and the presence of intrasutural Wormian bones. Forty-one specimens from 37 patients with isolated lambdoid synostosis were also studied pathologically. Only three cases showed bone union across the suture, which appears to be a result of closure rather than fusion as in other synostoses. The remainder of the cases showed varying degrees of increased cellular proliferation at the suture line, resulting in exaggerated and prolonged sutural activity. Morphologically, this produced increased interdigitation and fibrous adhesion between the suture margins.

Roentgen stereophotogrammetric analysis of restricted periods of neurocranial suture immobilization in rabbits

The effect of temporary fusion of sutures on craniofacial growth was studied biometrically in 4-week-old male New Zealand White rabbits. Tantalum bone markers were implanted in the cranial vault, and the coronal suture immobilized with isobutyl-2-cyanoacrylate adhesive. Linear craniectomy was performed after 2 or 6 weeks of sutural growth restriction (four animals in each group). The animals were followed for approximately 17 weeks. Early craniectomy resulted in greatly increased coronal suture bone separation (175% of control growth rates in peers and 125% of maximal control rates). Growth after late craniectomy showed an age-dependent lower rate, but still the overshoot markedly surpassed controls (210% of control rates in peers and 65% of maximal control growth rates). Overall, both exhibited overcompensation in coronal suture growth. A rapid compensation of adjacent sutures to temporary growth restriction and a tendency toward spontaneous correction following release of growth inhibition were demonstrated. Thus, the total anteroposterior growth of the combined frontonasal and coronal sutures nearly equaled that of control animals. Following linear craniectomy, volumetric calvarial expansion increased considerably in both early and late groups, due to compensatory coronal suture growth, but probably due also to spatial bone rearrangements. Based upon the findings, the length of the suture immobilization period seems critical to longitudinal and volumetric growth as well as to subsequent compensatory activity after surgical correction.

Experimental craniosynostosis in growing rabbits. The role of the periosteum

Reports on the role of the periosteum in premature sutural synostosis have been contradictory. The present study summarizes a series of six experiments designed to clarify these previously conflicting findings. Twenty-five male New Zealand White rabbits were divided into six experimental groups. In four of the groups, methyl-2-cyanoacrylate was used to glue the frontal and parietal bones together and temporarily immobilize the coronal suture. In the other two groups, the sutures were not immobilized. Polyethylene was used to separate the cyanoacrylate from the periosteum in two of the groups. The experiments were performed at 5 weeks of age, and the animals were killed at either 30, 45, or 180 days postoperatively. Metallic implants were placed in the frontal and parietal bones for monitoring growth and/or sutural immobilization. Sutural fusion was confirmed radiographically or histologically. Based upon the findings it seems that mechanical immobilization of a suture does not induce fusion of that suture in rabbits. Furthermore, it appears that the mere application of methyl-2-cyanoacrylate to the periosteum overlying a suture will consistently cause the formation of a bony bridge in growing rabbits but not in nongrowing animals. The adhesive does not consistently induce synostosis if the periosteum is excised.