Brzozowska, Iwona

Skrzat, Janusz

Walocha, Jerzy

Folia Morphologica

English

Jagiellonian Univeristy Repository

Folia Morphol. Vol. 63, No. 1, pp. 43–46Copyright © 2004 Via MedicaISSN 0015–5659www.fm.viamedica.pl O R I G I N A L  A R T I C L E43A preliminary study on the relationshipbetween the complexity of the sagittal sutureand cranial dimensionsJanusz Skrzat, Iwona Brzozowska, Jerzy WalochaDepartment of Anatomy, Collegium Medicum, Jagiellonian University, Kraków, Poland[Received 29 July 2003; Revised 7 October 2003; Accepted 8 October 2003]The paper presents the results obtained from analysis of the correlation be-tween cranial dimensions (length, width, and height) and indices against thecomplexity of the sagittal suture, which was expressed as the ratio betweenabsolute sutural length to the linear length of the suture. The statistical study on29 skulls shows a significant negative correlation between the height/width in-dex of all skulls and suture complexity (r = –0.78 for male, r = –0.70 for femaleskulls) and a negative correlation between cranial height and suture complexityin male skulls only (r = –0.49). This implies that lower and broader skulls havea more complicated sagittal suture. Correlations of the height/length and width//length ratios were assessed as statistically insignificant in both sexes.Key words: cranial indexes, sagittal suture, suture complexityAddress for correspondence: Dr Janusz Skrzat, Department of Anatomy, Collegium Medicum, Jagiellonian University, ul. Kopernika 12,31–034 Kraków, Poland, tel: +48 12 422 95 11, fax: +48 12 430 30 06, e-mail: jskrzat@poczta.onet.plINTRODUCTIONThe bones of the upper skull meet along five su-tures, which provide growing room for the rapidlyexpanding brain. The sagittal suture joins two pari-etal bones in the mid-sagittal plane and its protru-sions extend horizontally from edge to edge of twoopposing bones. The interdigitations, which arepresent along the opposing edges of the parietalbones, interlock precisely in the suture. The sagittalsuture can be serrate or dentate, thus facilitatinggreat resistance. This suture plays an important rolein normal cranial development and growth [9, 10].The sagittal suture enables transverse growth of theskull and the vault may considerably increase itswidth from childhood to adolescence. Otherwise, ifcranial growth is interrupted by premature ossifica-tion, a scaphocephalic skull results as a consequenceof sagittal synostosis. This disorder involves an ab-normal development of the skull and results in anunusually long and narrow head shape [11]. In spiteof numerous studies upon human crania, there hasbeen no extensive examination of the associationsbetween cranial dimensions and sutural complexity.It was because of the lack of data in the literatureconcerning this relationship that this study was un-dertaken. The aim of this study was, then, to evalu-ate whether the complexity of the sagittal suturecorrelates with cranial dimensions (length, width,height) and cranial indexes.MATERIAL AND METHODSAnalyses were performed on the non-obliteratedsagittal sutures of adult individuals. The skulls inves-tigated are housed in the collections of the Anato-mical Museum of the Anatomical Department of theJagiellonian University.The relationship between the complexity of thesagittal suture and cranial dimensions was studiedon a series of 29 human skulls (19 males and 10 fe-males). Analysis was performed on adult, non-de-formed dry skulls, with a clearly visible pattern ofsagittal suture on the external surface of the skull.44Folia Morphol., 2004, Vol. 63, No. 1The skulls studied were all without a metopic su-ture, which can be regarded as a continuation ofthe sagittal suture. The presence of a metopic su-ture may alter the rules of cranial growth and there-fore skulls with a metopic suture were rejected.An outline of the cranial suture was traced witha marker that could draw a thin line along the su-ture analysed on transparent tape, which had beenplaced on the external surface of the skull. Thesetraced silhouettes of cranial sutures were scannedwith a flat bat scanner and the digitised images thenprocessed to obtain a line of 1 pixel in width. Suchoutlines of cranial sutures were processed by soft-ware which enabled the length of the suture to bemeasured.Cranial measurements were taken on the exter-nal surface of the skull with a sliding calliper anda spreading calliper according to anthropologicalstandards [6, 7].Cranial dimensions were expressed by absolutediameters: maximum cranial length (g-op), maxi-mum cranial width (eu-eu) and cranial height (ba-b).The interrelationships between cranial diameters(length, width and height) were expressed by threecranial indices: (eu-eu/g-op)•100, (ba-b/g-op)•100,(ba-b/eu-eu)•100, which indicate the proportions be-tween cranial diameters and classify skulls as long,short, narrow, high, etc.Two measurements of the sagittal suture wereperformed to evaluate the coefficient of the suturalcomplexity (the linear length of the sagittal suture— the direct distance from bregma to lambda andthe total length of the sagittal suture — the lengthof the curved line that follows the outline of the su-ture). Sutural complexity was expressed as the ratiobetween absolute sutural length to the linear lengthof the suture.The relationship between the pairs of variablesexamined has been expressed in terms of the corre-lation coefficient. The significance level calculatedfor each correlation equalled 0.05. Since this param-eter is valid as a measure of relationship only if thetwo-dimensional distribution under examination isnormal, the variables analysed were statistically test-ed using the Shapiro-Wilks W test of normality. Ifthe W statistic is significant, then the hypothesis thatthe respective distribution is normal should be re-jected.RESULTSIn the case of the cranial variables studied thestatistic W of the Shapiro-Wilks test is not signifi-cant, so the normal distribution was accepted forthe data analysed.Mean values and the range of variation of thecraniometric data of the calvaria and the sagittalsutures are presented in the Tables 1 and 2. The cor-relation matrix of the metric traits under examina-tion is displayed in Tables 3 and 4.A statistically significant negative correlation be-tween cranial height and suture complexity was de-tected only in male skulls, while cranial length andwidth do not correlate significantly with suture com-plexity in either sex.Pearson’s correlation coefficient also supporteda strong negative correlation between suture com-plexity index (CI) and height/width index (ba-b/eu-eu).This correlation is statistically significant in both maleand female skulls. There is no significant correlationof the height/length and width/length index. It may,therefore, be concluded that complexity of the sagit-tal suture is related to the proportion between cra-nial height and width. This implies that skulls witha low width/height index have a more complicatedsagittal suture (Fig. 1). According to the classifica-tion of the width-height index these skulls will betermed tapeinocranus (range of index: x-91.9). Forthe skulls with a higher width/height index, the com-plexity index of the sagittal suture is lower and itsvalues depict instead their weakly complicated su-tures with a pattern of wavy lines.DISCUSSIONA number of studies have examined quantitativelycranial morphology and patterns of sutures but thereis no detailed evidence for the relationship betweensutural morphology and cranial dimensions or shape[2, 3, 5]. Measurements of suture complexity seemto be important for the study of cranial growth andit may be fruitful to evaluate temporal and geograph-ical variations in sutural morphology and its relationto the cranial dimension and form. This knowledgemight be helpful in racial taxonomy or sex determi-nation, if significant relationships between suturecomplexity and cranial dimensions could be estab-lished in distinct morphotypes.A cranial index expresses the interrelationshipbetween two defined dimensions of the skull andtherefore can be regarded as an indicator of cranialshape. Skull length, width and height measurementswere used to assess the influence of increased crani-al dimension on sutural complexity. The increase inskull dimensions is ultimately related to the growthof the brain [8]. The entire construction of the brain-45Janusz Skrzat et al., Complexity of the sagittal suture and cranial dimensionsTable 1. Statistical data of the skulls analysedVariable Sample Mean Minimum Maximum SdMale Female Male Female Male Female Male Female Male Femaleg-op 19 10 174.95 165.10  160.0 155.0 185.0 178.0 7.43 7.43eu-eu 19 10 142.79 139.30  129.0 131.0 155.0 147.0 7.15 4.30ba-b 19 10 131.00 127.40  120.0 118.0 145.0 135.0 6.16 5.62eu-eu/g-op 19 10 81.68 84.45  75.57 79.21 90.12 88.46 4.00 2.68ba-b/g-op 19 10 74.99 77.25  68.65 70.24 84.30 83.87 4.39 3.77ba-b/eu-eu 19 10 91.90 91.53  81.94 84.29 100.0 99.24 5.19 4.83Table 2. Mean and range of variation of the complexity of the sagittal sutureVariable Sample Mean Minimum Maximum SdMale Female Male Female Male Female Male Female Male FemaleCI 19 10 3.33 3.71 2.19 2.63 4.89 4.92 0.79 0.66Table 3. Correlation matrix of calvaria diameters and sag-ittal suture complexityDiameter                                     CIMale Femaleg-op 0.08 0.05eu-eu 0.44 0.38ba-b –0.49* –0.56*Denotes statistically significant correlation, p < 0.05Table 4. Correlation matrix of the cranial indices and sag-ittal suture complexityCranial index                                 CIMale Female(eu-eu/g-op)•100 0.38 0.27(ba-b/g-op)•100 –0.45 –0.56(ba-b/eu-eu)•100 –0.78* –0.70**Denotes statistically significant correlation, p < 0.05Figure 1. Correlation between the complexity index of the sagit-tal suture and the height/width cranial index for male skulls.case facilitates this process mainly thanks to the su-tures, which are the sites of bone growth and en-able a small amount of movement. On the otherhand the sutures must be strong enough to keepthe bones together and protect them from disloca-tion [4].The cranium and its sutures should be treated asone functional system, the components of whichcooperate during cranial morphogenesis. Otherwise,any disturbances of this system may cause severecranial and facial malformations [1]. During individ-ual development the dimensions of the calvaria di-rectly reflect the form of the growing neural mass,while the sutures have to counter separation of thecalvarial bones and permit motion between them.When the parietal bones are passively carried apartwith the expanding cerebral capsule, their areas areincreased by deposition of bone in the sutural mar-gins. They undergo significant morphological chang-es, which often produce an irregular shape of bonyedges involved in suture formation.In our study we hypothesised that variation inthe complexity of the sagittal suture is influenced byinteraction between the length, width and heightof the skull, which in turn are governed by expan-sion of the brain. This hypothesis was examined us-ing a group of adult skulls treated as a final result ofthe growth process.46Folia Morphol., 2004, Vol. 63, No. 1We only observed a negative correlation betweencranial height (ba-b) and suture complexity in maleskulls but a negative correlation between suture com-plexity and the width/height index was observed inboth sexes. These correlations probably reflect mor-phological relationships between the brain, craniumand the sagittal suture during the growth of the head.These can be explained in the following manner.With increased transverse diameter and limitedvertical growth, the parietal bones of the skulls weresubjected to separation from each other by intrinsicforces derived from the expanding brain. In this case,the sagittal suture be strong enough to prevent theparietal bones from lateral dislocation. This couldbe achieved by increased sutural complexity broughtabout by rapid osteogenesis in the sutural area andproducing a compensatory amount of bone.High skulls, in which the proportions betweenwidth and height are more or less equal, have a lesscomplicated sagittal suture than skulls with a lowwidth/height index,  as during cranial growth com-pensatory production of bone occurs not in the sag-ittal suture but in the sutures located in the lateralwall of the skull. In this case the parietal bones arenot subjected to extensive forces of separation butare instead elevated vertically by the growing brain.Here the low complexity of the sagittal suture mayresult from gradual osteogenesis in the sutural areaand lack of extensive counteraction to the transversedislocation of the parietal bones.From this study we conclude that the complexityof the sagittal suture is related to cranial dimensions(width and height) and their proportions, whereascranial length does not influence its complexity. Thuswe also presume that brain expansion in a verticalor transverse direction is, in contrast to midsagittalexpansion, crucial for determining the complexity ofthe sagittal suture.We tested our hypothesis on a cranial set whichdid not present a vast range of variability in cranialdiameter. A consistent result should be obtained inorder confirm the view that there is a mutual anddirect relation between cranial dimension and su-tural complexity.REFERENCES1. Anton SC, Jaslow CR, Swartz SM (1992) Sutural com-plexity in artificially deformed human (Homo sapiens)crania. J Morphol, 214: 321–332.2. Hauser G, Manzi G, Vienna A, De Stefano GF (1991)Dimension and shape of human cranial sutures— a new scoring method. Amer J Anat, 190: 231–244.3. Herring SW (1972) Sutures — a tool in functional cra-nial analysis. Acta Anat, 83: 222–247.4. Herring SW, Teng S (2000) Strain in the braincase andits sutures during function. Am J Phys Anthrop, 112:575–593.5. Jaslow CR (1990) Mechanical properties of cranial su-tures. J Biomech, 23: 313–321.6. Malinowski A, Wolański N (1988) Metody badańw biologii człowieka. PWN, Warszawa.7. Malinowski A, Bożiłow W (1997) Podstawy antro-pometrii. Metody, techniki, normy. PWN, Warszawa--Łódź.8. Moss (1960) A functional approach to craniology. AmJ Phys Anthrop, 18: 281–292.9. Opperman LA (2000) Cranial sutures as intramembra-nous bone growth sites. Dev Dyn, 219: 472–485.10. Outhof HA (1982) Sutural Growth. Acta Anat, 112: 58–68.11. Persson M (1995) The role of the sutures in normaland abnormal craniofacial growth. Acta OdontolScand, 53: 152–161.

A preliminary study on the relationship between the complexity of the sagittal suture and cranial dimensions

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A preliminary study on the relationship between the complexity of the sagittal suture and cranial dimensions

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