Characterization of craniofacial sutures using the finite element method

Characterizing the biomechanical behavior of sutures in the human craniofacial skeleton (CFS) is essential to understand the global impact of these articulations on load transmission, but is challenging due to the complexity of their interdigitated morphology, the multidirectional loading they are exposed to and the lack of well-defined suture material properties. This study aimed to quantify the impact of morphological features, direction of loading and suture material properties on the mechanical behavior of sutures and surrounding bone in the CFS. Thirty-six idealized finite element (FE) models were developed. One additional specimen-specific FE model was developed based on the morphology obtained from a µCT scan to represent the morphological complexity inherent in CFS sutures. Outcome variables of strain energy (SE) and von Mises stress (σ_vm) were evaluated to characterize the sutures’ biomechanical behavior. Loading direction was found to impact the relationship between SE and interdigitation index and yielded varied patterns of σ_vm in both the suture and surrounding bone. Adding bone connectivity reduced suture strain energy and altered the σ_vm distribution. Incorporating transversely isotropic material properties was found to reduce SE, but had little impact on stress patterns. High-resolution µCT scanning of the suture revealed a complex morphology with areas of high and low interdigitations. The specimen specific suture model results were reflective of SE absorption and σ_vm distribution patterns consistent with the simplified FE results. Suture mechanical behavior is impacted by morphologic factors (interdigitation and connectivity), which may be optimized for regional loading within the CFS.     

Cranial Suture Morphology and its Relationship to Diet in Cebus

Cranial sutures are complex morphological structures. Four Cebus species (C. albifrons, C. apella, C. capucinus, C. olivaceus) are used here to test the hypothesis that sagittal suture complexity is enhanced in animals that eat materially challenging foods. These primates are ideal for such comparative studies because they are closely related and some are known to exhibit differences in the material properties of the foods they ingest and masticate. Specifically, Cebus apella is notable among members of this genus for ingesting food items of high toughness as well as consistently demonstrating a relatively robust cranial morphology. Consistent with previous studies, C. apella demonstrates significantly more robust mandibular and temporal fossa morphology. Also, C. apella possesses sagittal sutures that are more complex than congenerics. These data are used to support the hypothesis that cranial suture complexity is increased in response to consuming diets with more obdurate material properties. One interpretation of this hypothesis is that, compared to non-apelloids, total strain in the apelloid cranial suture connective tissue environment is elevated due to increased jaw muscle activity by increases in either force magnitudes or the number of chewing events. It is argued that greater masticatory function enhances the growth and modeling of cranial suture interdigitation. These data show that cranial suture complexity is one more hard tissue feature from the skull that might be used to inform hypotheses of dietary functional morphology.     

Bundles of Spider Silk,Braided into Sutures,Resist Basic Cyclic Tests: Potential Use for Flexor Tendon Repair

Repair success for injuries to the flexor tendon in the hand is often limited by the in vivo behaviour of the suture used for repair. Common problems associated with the choice of suture material include increased risk of infection, foreign body reactions, and inappropriate mechanical responses, particularly decreases in mechanical properties over time. Improved suture materials are therefore needed. As high-performance materials with excellent tensile strength, spider silk fibres are an extremely promising candidate for use in surgical sutures. However, the mechanical behaviour of sutures comprised of individual silk fibres braided together has not been thoroughly investigated. In the present study, we characterise the maximum tensile strength, stress, strain, elastic modulus, and fatigue response of silk sutures produced using different braiding methods to investigate the influence of braiding on the tensile properties of the sutures. The mechanical properties of conventional surgical sutures are also characterised to assess whether silk offers any advantages over conventional suture materials. The results demonstrate that braiding single spider silk fibres together produces strong sutures with excellent fatigue behaviour; the braided silk sutures exhibited tensile strengths comparable to those of conventional sutures and no loss of strength over 1000 fatigue cycles. In addition, the braiding technique had a significant influence on the tensile properties of the braided silk sutures. These results suggest that braided spider silk could be suitable for use as sutures in flexor tendon repair, providing similar tensile behaviour and improved fatigue properties compared with conventional suture materials.     

Calvarial suture interdigitation in hadrosaurids (Ornithischia: Ornithopoda): Perspectives through ontogeny and evolution

Lambeosaurine hadrosaurids exhibited extreme modifications to the skull, where the premaxillae, nasals, and prefrontals were modified to form their iconic supracranial crests. This morphology contrasts with their sister group, Hadrosaurinae, which possessed the plesiomorphic arrangement of bones. Although studies have discussed differences between lambeosaurine and hadrosaurine skull morphology and ontogeny, there is little information detailing suture modifications through ontogeny and evolution. Suture morphology is of particular interest due to its correlation with the mechanical loading of the skull in extant vertebrates. We quantify and contrast the morphology of calvarial sutures in iguanodontians and ontogenetic series of Corythosaurus and Gryposaurus to test whether the evolution of lambeosaurine crests impacted the mechanical loading of the skull. We found that suture interdigitation (SI) increases through ontogeny in hadrosaurids, although this increase is more extreme in Corythosaurus than Gryposaurus, and overall suture complexity (i.e., overall shape) remained constant. Lambeosaurines also have higher SI than other iguanodontians, even in crestless juveniles, suggesting that increased sinuosity is unrelated to the structural support of the crest. Hadrosaurines and basal iguanodontians did not differ. Similarly, lambeosaurines have more complexly shaped sutures than hadrosaurines and basal iguanodontians, while the latter two groups do not differ. Taken together, these results suggest that lambeosaurine calvarial sutures are more interdigitated than other iguanodontians, and although suture sinuosity increased through ontogeny, the suture shape remained constant. These ontogenetic and evolutionary patterns suggest that increased suture complexity in lambeosaurines coincided with crest evolution, and corresponding modifications to their facial skeleton altered the distribution of stress while feeding.     

Mechanics of cranial sutures using the finite element method

To investigate how cranial suture morphology and the arrangement of sutural collagen fibres respond to compressive and tensile loads, an idealised bone–suture–bone complex was analysed using a two-dimensional finite element model. Three suture morphologies were simulated with an increasing interdigitation index (I.I.): butt-ended, moderate interdigitated, and complex interdigitated. The collagen matrix within all sutures was modelled as an isotropic material, and as an orthotropic material in the interdigitated sutures with fibre alignment as reported in studies of miniature pigs. Static uniform compressive or tensile loading was applied to the complex. In interdigitated sutures with isotropic material properties, the orientation of the maximum (tensile) principal stresses within the suture matched the collagen fibre orientation observed in compressed and tensed sutures of miniature pigs. This suggests that randomly arranged sutural collagen fibres could optimise to an orientation most appropriate to withstand the predominant type of loading. A compression-resistant fibre arrangement imparted the highest suture strain energy relative to the isotropic and tension-resistant arrangements, indicating that this configuration maximises energy storage. A comparison across the different suture morphologies indicated that bone strain energy generally decreased with a decrease in I.I., irrespective of the sutural fibre arrangement. However, high bone stress at the interdigitation apices shifted to the limbs of the suture with an increase in I.I. These combined findings highlight the importance of suture morphology and anisotropy as properties having a significant influence on sutural mechanics.     

Changing the convexity and concavity of nasal cartilages and cartilage grafts with horizontal mattress sutures: part I. Experimental results

Prior studies indicated that horizontal mattress sutures can control the curvature of a convex lateral crus. This study undertook to ascertain the ideal spacing for mattress sutures, determine what effect they have on the subsequent strength of the cartilage, and compare that to the resultant strength after scoring procedures used to control curvature. Curved fresh cadaver septa of various thicknesses (0.5, 1, and 1.5 mm) were used. The ideal spacing (gap between suture purchases) for the mattress suture was sought in 15 specimens. The consequent change in stiffness (modulus) of the cartilage was measured in nine other specimens before and after suture placement and after scoring. If the spacing was too large, instability resulted. If it was too small, curvature correction could not be obtained. An ideal mattress spacing (6 to 8 mm for 0.5-mm specimens and 8 to 10 mm for 1.5-mm specimens) removed most curvature and provided stability. The mattress suture increased the stiffness (modulus) above normal and far above that when the curvature was removed by scoring. The mean composite modulus before suturing was 4.6 MPa. After ideally spaced sutures, it was 6.2 MPa, a 35 percent increase in stiffness. After scoring to improve curvature, it was 2.4 MPa, a 48 percent reduction in stiffness (p = 0.02, Wilcoxon signed rank test). The horizontal mattress suture technique corrects cartilage curvature if the appropriate spacing is used. The corrected cartilage is stiffer/stronger than normal cartilage and much stiffer/stronger than if scored.     

Cranial suture complexity in white-tailed deer (Odocoileus virginianus)

Neurocranial expansion and mastication are commonly implicated as the two major biomechanical factors affecting suture morphology. In deer the antlers provide an additional source of biomechanical stress acting on the skull. Equivalent stresses are not found in females, who lack antlers. We analyzed the complexity and interdigitation of the interfrontal and coronal sutures that surround the antler-bearing frontal bones of (n = 67) white-tailed deer (Odocoileus virginianus) to 1) evaluate changes in suture morphology throughout ontogeny, and 2) test the hypothesis that male deer have more complex sutures than females. Two methods were used to quantify suture morphology: fractal analysis and length-ratios (actual suture length divided by direct straightline length). Both techniques produced similar results, although the two methods cannot be considered equivalent. Suture complexity increases markedly throughout ontogeny, but appears to level off after animals have reached adulthood. Cranial size in males, but not females, continues to increase in adults. No significant increase in suture complexity with age in the adult cohort was detected. While deer are highly dimorphic in size and the presence of antlers, no significant differences existed between males and females for any measure of suture complexity. No consistent patterns emerged between suture complexity and skull size or antler characteristics. The presence of antlers appears to have a minimal effect on suture complexity in white-tailed deer. Factors that may contribute to the lack of dimorphism in suture complexity are discussed.     

Evaluation of four methods of flexor tendon repair for postoperative active mobilization

Active mobilization of repaired flexor tendons requires sufficient suture strength. This study was designed to investigate the suitability of four newly developed and comparatively strong tendon sutures for flexor tendon repair with active digital mobilization. Fifty fresh flexor digitorum profundus tendons were randomly assigned to five groups and repaired using the Tang, cruciate, Robertson, Silfverskiold, and modified Kessler suture methods. The repaired tendons were subjected to mechanical testing in an Instron tensile machine to determine the 2-mm gap formation force, ultimate strength, elastic modulus, and energy to failure of the sutures. The 2-mm gap formation forces of the sutures were 43.0 N for the Tang, 37.4 N for the cruciate, 25.0 N for the Robertson, 32.3 N for the Silfverskiold, and 21.2 N for the modified Kessler methods. The ultimate strength of the sutures was 53.6 N for the Tang, 46.3 N for the cruciate, 41.6 N for the Robertson, 41.0 N for the Silfverskiold, and 24.7 N for the modified Kessler methods. Statistically, the gap formation force and ultimate strength were the highest in the Tang, higher in the cruciate, and the lowest for the Robertson and the modified Kessler methods. The elastic modulus of the repaired tendons, as represented by the linear slope of the force-displacement curve, was also statistically the largest in the Tang, larger in the cruciate, and lowest for the Robertson and modified Kessler methods. Energy to failure was statistically the largest in the Tang, higher in the cruciate, lower in the Silfverskiold and the Robertson, and the lowest for the modified Kessler methods. It was concluded that significant differences exist in mechanical properties of the newly developed tendon suture methods. Among the methods for tendon repair that were tested, the Tang and the cruciate sutures were the best candidates for flexor tendon repair in the hand with postoperative active mobilization because of their superior tensile strength, elastic properties, energy to failure, and reasonable operation time.     

Multiscale characterization and micromechanical modeling of crop stem materials

An essential prerequisite for the efficient biomechanical tailoring of crops is to accurately relate mechanical behavior to compositional and morphological properties across different length scales. In this article, we develop a multiscale approach to predict macroscale stiffness and strength properties of crop stem materials from their hierarchical microstructure. We first discuss the experimental multiscale characterization based on microimaging (micro-CT, light microscopy, transmission electron microscopy) and chemical analysis, with a particular focus on oat stems. We then derive in detail a general micromechanics-based model of macroscale stiffness and strength. We specify our model for oats and validate it against a series of bending experiments that we conducted with oat stem samples. In the context of biomechanical tailoring, we demonstrate that our model can predict the effects of genetic modifications of microscale composition and morphology on macroscale mechanical properties of thale cress that is available in the literature.

     

Cranial suture complexity in caviomorph rodents (Rodentia; Ctenohystrica)

Due to their flexibility, sutures are regions that experience greater strains than the surrounding rigid cranial bones. Cranial sutures differ in their degree of interdigitation or complexity. There is evidence indicating that a more convoluted suture better enables the absorption of high stresses coming from dynamic masticatory forces, and other functions. The Order Rodentia is an interesting clade to study this because of its taxa with diverse chewing modes. Due to repeated loading resulting from gnawing and grinding, energy absorption by the sutures might be a crucial factor in these mammals. Species within the infraorder Caviomorpha were chosen as a case study because of their ecomorphological and dietary diversity. This study compared five sutures from the rostrum and cranial vault across seven caviomorph families, and assessed their complexity by means of the relative length and fractal dimension. Across these rodents, cranial sutures are morphologically quite diverse. We found that the sutures connecting the rostrum with the vault were relatively more interdigitated than those in the cranial vault itself, especially premaxillofrontal sutures. Suture interdigitation was higher in species that display chisel‐tooth digging and burrowing behaviors, especially in the families Ctenomyidae and Octodontidae, than those in families Dasyproctidae and Cuniculidae, which have more gracile masticatory systems. The reconstruction of the ancestral character state, on family and species phylogeny, points toward low suture interdigitation (i.e., low length ratio) as a likely ancestral state for interfrontal, premaxillofrontal and maxillofrontal sutures. Interspecific differences in suture morphology shown here might represent adaptations to different mechanical demands (i.e., soft vs. tough foods) or behaviors (e.g., chisel‐tooth digging), which evolved in close association with the diverse environments occupied by caviomorph rodents.     

Fractal analysis of sagittal suture morphology

Quantifying shape is a broad problem in the morphological sciences. Most techniques for numerically describing shape abstract the shape into the most logical ideal Euclidean dimension. The fractional, or fractal, dimension is a simple computation that expresses shape in real, rather than ideal, space. The structured walk technique developed for the fractal analysis of rugged boundaries is applied here to the contour of the human sagittal suture in order to discriminate the separate morphological patterns of interfingering and interlocking. These attributes contribute differentially to the suture's “complexity,” a concept often used in biomechanical hypotheses. Previous techniques for estimating sutural complexity do not isolate small-scale from large-scale morphological patterns. Results indicate that despite the visual appearance of great variation, human sagittal sutures are remarkably consistent in the degree of complexity expressed separately by large-scale interfingering lateral excursions and small-scale interlocking ruggedness. There is no significant correlation between the absolute or bregma-lambda chord length of the human sagittal suture and its degree of complexity as determined by the structured walk technique.     

Adenovirus-mediated transmission of a dominant negative transforming growth factor-beta receptor inhibits in vitro mouse cranial suture fusion

Recent studies have implicated the transforming growth factor (TGF)-beta family in the regulation of pathological sporadic cranial suture fusion. In addition, these studies have shown that TGF-beta is highly expressed by the dura mater underlying fusing murine cranial sutures. The purpose of the present experiments was to analyze the effects of disrupting TGF-beta signaling during programmed mouse cranial suture fusion. Using recombinant DNA technology, a replication-deficient adenovirus encoding a defective TGF-beta receptor (Ad.DN-TbetaRII) capable of blocking TGF-beta biological activity was constructed. Mouse posterior frontal sutures were harvested before the initiation of suture fusion (postnatal day 25), and the dura mater underlying the suture was infected with vehicle, Ad.DN-TbetaRII, or control virus (Ad.LacZ; n = 10 each). Sutures were cultured for 14 or 30 days in an organ culture system and analyzed macroscopically and histologically.X-gal staining of Ad.LacZ-infected sutures 14 days after culture revealed strong staining of cells localized to the dura mater. Macroscopic analysis revealed complete sutural fusion in vehicle and Ad.LacZ-infected sutures. In contrast, Ad.DN-TBRII-infected sutures demonstrated nearly complete patency. Histological analysis confirmed our macroscopic observations with sutural fusion in 81.3 +/- 10 percent and 74.5 +/- 9 percent of vehicle and Ad.LacZ-infected sutures, respectively, versus 38.1 +/- 12 percent (p < 0.001) in Ad.DN-TbetaRII-infected sutures. In addition, transfection with the Ad.DN-TbetaRII virus resulted in a significant attenuation of anterior-to-posterior suture fusion, with the majority of fused sections localized to anterior sections. These data strongly implicate TGF-beta biological activity in the dura mater underlying the posterior frontal suture in the regulation of programmed sutural fusion. In addition, this study demonstrates the utility of adenovirus-mediated gene transfer in preventing programmed sutural fusion.     

Mechanics of cranial sutures during simulated cyclic loading

Previous computational and experimental analyses revealed that cranial sutures, fibrous joints between the bones, can reduce the strain experienced by the surrounding skull bones during mastication. This damping effect reflects the importance of including sutures in finite element (FE) analyses of the skull. Using the FE method, the behaviour of three suture morphologies of increasing complexity (butt-ended, moderate interdigitated, and complex interdigitated) during static loading was recently investigated, and the sutures were assumed to have linear elastic properties. In the current study, viscoelastic properties, derived from published experimental results of the nasofrontal suture of young pigs (Sus scrofa), are applied to the three idealised bone-suture models. The effects of suture viscoelasticity on the stress, strain, and strain energy in the models were computed for three different frequencies (corresponding to periods of 1, 10, and 100s) and compared to the results of a static, linear elastic analysis. The range of applied frequencies broadly represents different physiological activities, with the highest frequency simulating mastication and the lowest frequency simulating growth and pressure of the surrounding tissues. Comparing across all three suture morphologies, strain energy and strain in the suture decreased with the increase in suture complexity. For each suture model, the magnitude of strain decreased with an increase in frequency, and the magnitudes were similar for both the elastic and 1s frequency analyses. In addition, a viscous response is less apparent in the higher frequency analyses, indicating that viscous properties are less important to the behaviour of the suture during those analyses. The FE results suggest that implementation of viscoelastic properties may not be necessary for computational studies of skull behaviour during masticatory loading but instead might be more relevant for studies examining lower frequency physiological activities.     

Nasal capsular cartilage is required for rat transpalatal suture morphogenesis

In the cranial vault, suture morphogenesis occurs when the growing cranial bones approximate and overlap or abut one another. Patency of developing sutures is regulated by the underlying dura mater. Once cranial sutures form, bone growth proceeds from the sutures in response to growth signals from the rapidly expanding neurocranium. Facial sutures do not develop in contact with the dura mater. It was therefore hypothesized that facial suture morphogenesis and bone growth from facial sutures are regulated by tissues with an equivalent role to the dura mater. The present study was designed to test this hypothesis by characterizing the morphology and growth factor expression in developing transpalatal (TP) sutures and their surrounding tissues, and then assessing the role of the overlying nasal capsular (NC) cartilages in maintaining suture patency. TP sutures develop as overlapping sutures, similar to cranial coronal sutures, and expression of Tgf-betas in TP sutures was similar to their distribution in cranial coronal sutures. To establish whether NC cartilages play a role in regulating TP suture morphogenesis, fetal rat TP sutures were cultured with associated attached NC cartilages or with NC cartilages removed. Sutures cultured for upward of 5 days with intact NC cartilages remained patent and maintained their cellular and fibrous components. However, in the absence of NC cartilages, the cellular nature of the sutures was not maintained and they became progressively acellular, with bony bridging across the suture. This finding is similar to that for cranial vault sutures cultured in the absence of dura mater, indicating that NC cartilages play an equivalent role to dura mater in maintaining the patency of developing sutures. These studies indicate that tissue interactions likely regulate morphogenesis of all cranial and facial sutures.     

Linking form and function of the fibrous joints in the skull: a new quantification scheme for cranial sutures using the extant fish Polypterus endlicherii

The aim of this study is to connect specific sutural morphologies with the specific types of deformation they experience. To meet this goal, we quantified the morphologies of the interfrontal (IF), interparietal (IP), and frontoparietal (FP) sutures in the extant fish Polypterus endlicherii, and used our published measurements of in vivo deformation of these sutures during feeding to infer how suture morphology and function are connected. Specifically, we found that three relatively simple measures of cross-sectional suture complexity (i.e., the ratio of total sutural length to its shortest end-to-end length; amount of sutural overlap; and size of the largest interdigitation) can be used to distinguish between the IF, FP, and IP sutures, which exhibit very different cross-sectional shapes and responses to loading. Interestingly, these differences in cross-sectional morphology are not reflected by the linear traces of these sutures on the surface of the skull, implying that cross-sectional shape of a suture must be known to infer the loading conditions it experiences. Plotting the three cross-sectional metrics against one another to yield a sutural morphospace shows that the IF, IP, and FP sutures define regions that are largely distinct from one another. Our previous measurements of strain across these sutures suggested that the FP region would lie between the IF and IP regions; instead, the FP region is largely set apart from the other two fields. Based on this discovery, and on the locations of cranial muscles, we propose a new model of deformation in the skull of P. endlicherii during feeding, in which rotation parallel to the skull roof is combined with bending, subjecting the FP suture to complex shearing. Finally, although the sutures of P. endlicherii appear to be significantly less complex than those of mammals, these fish sutures show a similar range of morphologies and perform similar functions as do mammalian sutures.     

Fractal morphometry of cell complexity.

Irregularity and self-similarity under scale changes are the main attributes of the morphological complexity of both normal and abnormal cells and tissues. In other words, the shape of a self-similar object does not change when the scale of measurement changes, because each part of it looks similar to the original object. However, the size and geometrical parameters of an irregular object do differ when it is examined at increasing resolution, which reveals more details. Significant progress has been made over the past three decades in understanding how irregular shapes and structures in the physical and biological sciences can be analysed. Dominant influences have been the discovery of a new practical geometry of Nature, now known as fractal geometry, and the continuous improvements in computation capabilities. Unlike conventional Euclidean geometry, which was developed to describe regular and ideal geometrical shapes which are practically unknown in nature, fractal geometry can be used to measure the fractal dimension, contour length, surface area and other dimension parameters of almost all irregular and complex biological tissues. We have used selected examples to illustrate the application of the fractal principle to measuring irregular and complex membrane ultrastructures of cells at specific functional and pathological stage.     

Strain accommodation in the zygomatic arch of the pig: A validation study using digital speckle pattern interferometry and finite element analysis

It has been repeatedly suggested that mammalian cranial sutures act not only to allow growth but also to reduce the levels of strain experienced by the skull during feeding. However, because of the added complexity they introduce, sutures are rarely included in finite element (FE) models, despite their potential to influence strain results. Because sutures present different morphologies and with differing degrees of internal fusion, many different methods of modeling may be necessary to accurately measure strain environments. Alternatively, these variables may exert very little influence on the scale of a whole‐skull model. To validate suture modeling methods, four alternative ways of including a suture in 3D FE models of the pig zygomatic arch were considered and compared with ex vivo experimental data from digital speckle pattern interferometry (DSPI). The use of DSPI rather than traditional strain gauge techniques allows strain gradients around the suture as well as the motions of the two bones to be observed. Results show that the introduction of 3D elements assigned more compliant material properties than the surrounding bone, is the most effective way of modeling both morphologies of suture, both in tension and compression. However, models containing no suture are almost indistinguishable from these compliant suture models, beyond the high strain gradient immediately adjacent to the suture. Conversely, modeling the suture as an open break in the mesh, or with spring elements assigned suture properties, fails to reproduce the experiment. Thus, although a solid but flexible model of sutures is preferred, the similarity between these models and those without sutures tentatively suggests that such extra detail may be unnecessary in pigs if the behavior of the whole skull is of interest. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

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.     

Sexual dimorphism of cranial suture complexity in wild sheep (Ovis orientalis)

Sutural complexity (the degree of interdigitation) of 13 cranial sutures was compared between male and female wild sheep ( Ovis orientalis ) to investigate a morphological feature that is potentially important with respect to stress transmission in the skulls of males during fighting. Most facial sutures (four of six) were not sexually dimorphic, but two sutures, the maxillojugal and jugolacrimal, had greater complexity in males than in females, suggesting that significant forces may be transmitted through the facial region of rams, most likely during horn clashing. Most of the braincase sutures (five of seven) were more complex in males than in females, and different factors appear to underlie this sexual dimorphism. In females, increased complexity of sutures during ontogeny was predicted best by variables measuring growth of the skull, brain or face, while in males, changes in complexity were predicted best by variables representing mechanical loading and frontal bone growth.