Sternum has a great clinical significance, considering that median sternotomy is the most common surgical approach
used in cardiac surgery. The aim of this study is to standardize the sternum according to size, shape and sex and to obtain ranges of the »standard sternum«. The study was done on 55 male and 35 female sterna of the average age of 65. Complex morphometric analysis of breadth, length and thickness of the sterna were performed on sternal segments
which were defined by costal notches. Morphometric analysis shows that the general sternum structure in the females
and in the males is equal. The standard dimensions of female and male sternum were determined. Standardization according to shape suggests that there is one standard sternum shape present in more than 2/3 of analysed samples of both sexes

Igor Lekšan

Radivoje Radić

Robert Selthofer

Tomislav Mrčela

Vasilije Nikolić

English

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Coll. Antropol. 30 (2006) 1: 43–47Original scientific paperMorphometric Analysis of the SternumRobert Selthofer1, Vasilije Nikoli}1, Tomislav Mr~ela2, Radivoje Radi}1, Igor Lek{an1,Igor Rude`3 and Kristina Selthofer41 Department of Anatomy, School of Medicine, University »J. J. Strossmayer«, Osijek, Croatia2 Faculty of Electrical Engineering, University »J. J. Strossmayer«, Osijek, Croatia3 Department of Cardiac Surgery, University Hospital Dubrava, Zagreb, Croatia4 Department of Cardiology, University Hospital Osijek, Osijek, CroatiaA B S T R A C TSternum has a great clinical significance, considering that median sternotomy is the most common surgical ap-proach used in cardiac surgery. The aim of this study is to standardize the sternum according to size, shape and sex andto obtain ranges of the »standard sternum«. The study was done on 55 male and 35 female sterna of the average age of65. Complex morphometric analysis of breadth, length and thickness of the sterna were performed on sternal segmentswhich were defined by costal notches. Morphometric analysis shows that the general sternum structure in the femalesand in the males is equal. The standard dimensions of female and male sternum were determined. Standardization ac-cording to shape suggests that there is one standard sternum shape present in more than 2/3 of analysed samples of bothsexes.Key words: sternum, morphometric analyse, median sternotomyIntroductionSternum (the breastbone) is a flat bone situated verti-cally in the median and anterior part of the thoracic skel-eton. It has a great clinical significance, considering thatmedian sternotomy is the most common surgical ap-proach used in cardiac surgery. When applying this surgi-cal intervention, the sternum is cut through in midlinefrom the jugular notch to the xiphoid process and thusaccess to the anterior mediastinal organs, especially tothe heart and major blood vessels is gained1,2.Dehiscence of the sternotomy closure and consequen-tial separation of the sternum halves as well as develop-ment of deep mediastinitis is a relatively rare but a seri-ous complication. Incidence rate is between 0.5–2.5%3,but some studies show that it can be higher, even up to8%4. Suture dehiscences may be influenced by variousfactors, such as suture technique, osteoporosis level, sex,comorbidity, various perioperative and postoperative fac-tors and many others5,6.Clinical significance of the sternum is also manifestedduring procedures of cardiopulmonary resuscitation. Ster-num fracture is common consequence of active compres-sive-decompressive cardiopulmonary resuscitation (ACD-–CPR), in other words of artificial respiration and heartmassage. Fractures sustained during this procedure maycause severe heart injuries which often lead to patient'sdeath7,8. Studies conducted on cadavers show that ster-num fractures are more common in the females over 509.The important factor causing fractures, besides osteopo-rosis, is considered to be the fact that female sternum isconsiderably thinner than the male and therefore moreprone to fractures10. With regard to exceptional variabil-ity of sternum dimensions and shape, it is very probablethat divergence from »standard sternum« may also influ-ence occurrence of sternal dehiscence and cause prone-ness to fractures. Despite that, morphometry of differentorgans and parts of the skeleton is well known11, data ofthe sternum morphology and morphometry are still in-suficient12. Those findings are of great importance in an-thropological researches13,14.The aim of this study is to standardize the sternumaccording to size, shape and sex by applying complexmorphometric analysis, and to obtain ranges of the »stand-ard sternum« according to the sex and to the individualdimensions.43Received for publication November 17, 2005Materials and MethodsMaterial for the present study consisted of 90 humansterna: 35 female and 55 male, of the average age of 65.The specimens were taken from osteological collection ofFaculty of Medicine, Department of Anatomy at the Uni-versity »J. J. Strossmayer« in Osijek, Croatia. Specimenswere fixated in formalin solution over three month. Com-plex morphometric analysis was performed15,16.Total sternum length, sternal angle, breadth, lengthand thickness of the manubrium and the body of thesternum were measured.Total sternum length is the distance measured fromthe jugular notch to the xiphoid process end17. Whilemeasuring the sternal angle, the sternum was set downand fixed in the lateral position at the right angle. On theunderground below the sternum, next to the sternumposterior surface, the points were marked immediatelybelow the sternal synchondrosis, next to the lower end ofclavicular notch and below the lower end of the fourthcostal notch. The sternal angle was determined by draw-ing lines to join the points marked on the underground.Sternal angle was measured with a protractor with preci-sion of 0.5º.The breadth, length and thickness of the manubriumand the body of the sternum were also determined (Fig-ure 1). The manubrium breadth was measured in thearea below the first costal notch and in the superior endof the second costal notch, in other words immediatelyabove the sternal synchondrosis. These were the pointson the samples representing the least and the greatestmanubrium breadth. The body breadth was measured onseveral points: in the middle of the distance between thesecond and third, the third and fourth, the fourth andfifth, the fifth and sixth and between the sixth and sev-enth costal notches. The manubrium thickness was mea-sured on two points which represent extreme values ofmanubrium thickness. The greatest thickness was mea-sured at the intersection of the central longitudinal lineand the line joining central points of clavicular notches.The least thickness was determined at the point wherethe central longitudinal line intersected manubrium atthe middle of its length. The samples were measured formanubrium length, the length between the second andfourth costal notches, the length from the fourth costalnotch to the xiphoid process and the length of the xiphoidprocess. The manubrium length was determined by mea-suring the distance between the centre of the jugularnotch and the centre of the sternal synchondrosis. Thebreadth, length and thickness of the sternum were mea-sured with micrometer with precision of 0.1 mm.ResultsMorphometric analyse shows that the proportionalsternum structure in the females and in the males isequal. Indexes of manubrium breadth and length propor-tion as well as of body of the sternum breadth and lengthproportion are almost identical in sterni of both sexes(Table 1). The greatest manubrium breadth is approxi-mately equal or greater than its length, while the aver-age body of the sternum breadth equals approximately1/3 of its length. There is no statistical significance insternal angle values.Knowledge of general sternum structure and of theresults of comprehensive morphometric analysis leads toconclusion that there is »standard or typical sternum«.Although general sternum structure in males and in fe-males is almost identical, there are significant sex differ-R. Selthofer et al.: Morphometric Analysis of the Sternum, Coll. Antropol. 30 (2006) 1: 43–4744Fig. 1. Breadth, length, thickness of the sternum segments andtotal length of the sternum.TABLE 1MANUBRIUM INDEX, BODY OF THE STERNUM INDEX AND STERNUM ANGLEFemale(X±SD, cm)Male(X±SD, cm)t pIM 1.18±0.16 1.24±0.17 1.21 0.23IC 0.29±0.07 0.29±0.06 –0.28 0.78Sternum angle 165.30±7.19 166.35±7.38 0.37 0.71IM – manubrium index (manubrium width / manubrium length), IC – body of the sternum index (sternum body width / sternum bodylength)ences in absolute values of the most of measured parame-ters. Standard sternum dimensions are determined asmean value of measured parameters with divergence ofone standard deviation (Table 2). Analysis of these di-mensions shows that more than 2/3 of sternum speci-mens regardless of sex belong to the »standard sternum«group according to their dimensions.After measuring sternum breadth section by section,where each section is determined by costal cartilage at-tachments to the breastbone, the obtained data suggestthat there are different shapes of manubrium and bodyof the sternum.Typical or standard shape was determined as meanvalue of measured parameters with divergence of onestandard deviation. When morphometric measures di-verge more than one standard deviation, the sternumhas atypical or non-standard shape.Manubrium shape was determined according to pro-portions of the least and the greatest breadth, that is theproportion between the breadths measured immediatelyabove the second costal notch and the breadth betweenclavicular notches.Body of the sternum shape was determined accordingto the proportion of basic and the greatest sternumbreadth. In male samples it is measured between thefifth and sixth costal notches and in female samples be-tween the fourth and fifth costal notches.Basic corpus sterni breadth is average breadth mea-sured between the second and third and between sixthand seventh costal notches, because it was noticed thatthe upper and the lower part of the body of the sternumhave constant breadth. The middle part varies most insingle sections breadth and therefore this part is respon-sible for shape variations. Results show that there is onestandard, typical shape that more than 2/3 of analysedspecimens have. Identical shapes and almost identical in-cidence of shapes are found in both sexes. Standardmanubrium has trapezoid shape, which is deter- minedby breadth proportion of 0.50 in females and 0.53 inmales. The remaining third of specimens is divided intoextreme groups that diverge from standard shape (Table3). The values of manubrium breadth proportions lowerthan one standard deviation determine triangular manu-brium shape, while the values higher than one standarddeviation determine quadrangular shape. Standard sha-pe of the body of the sternum, named longitudinal ovalshape, is determined by proportion that is 0.64 in femalesand 0.76 in males. O-shape of the body of the sternum isnoticed in sterni where the breadth proportions are morethan one standard deviation lower, while the body wherethe proportion is more than one standard deviation high-er has flat shape (Figure 2).DiscussionComplications in heart surgeries are frequently con-nected with suture dehiscence of the sternum and devel-opment of deep mediastinitis which is followed by highmortality rate6,18,19.Results show that there is general sternum structureequal for both sexes. However, the absolute values ofmeasured parameters are significantly different. Femalesternum is on average shorter, narrower and thinnerthan male sternum. Previous studies indicate that fe-male sex is additional risk factor for suture dehiscence ofthe sternum20.R. Selthofer et al.: Morphometric Analysis of the Sternum, Coll. Antropol. 30 (2006) 1: 43–4745TABLE 2STANDARD FEMALE AND MALE STERNUMManubriumFemale(X±SD)Male(X±SD)pMax. Breadth (cm) 6.06±0.81 6.82±0.80 <0.05Min. Breadth (cm) 3.13±0.33 3.68±0.55 <0.05Average breadth (cm) 4.59±0.50 5.25±0.68 <0.05Length (cm) 5.24±0.45 5.52±0.36 <0.05Average thickness (cm) 1.12±0.09 1.26±0.19 <0.05Area (cm2) 24.13±3.71 28.98±3.48 <0.05Volume (cm3) 27.49±5.53 37.33±6.30 <0.05BodyAverage breadth (cm) 2.71±0.31 3.07±0.43 <0.05Length (cm) 9.42±1.40 10.97±1.44 <0.05Average thickness (cm) 0.92±0.12 1.00±0.11 <0.05Area (cm2) 26.14±4.79 34.80±5.50 <0.05Volume (cm3) 24.35±5.94 35.08±6.81 <0.05SternumTotal length (cm) 18.29±1.74 20.86±1.46 <0.05Area (cm2) 50.26±7.45 63.86±7.68 <0.05Volume (cm3) 51.84±10.57 72.42±11.54 <0.05TABLE 3INCIDENCE OF STERNUM SHAPES ACCORDING TO SEXMandibulariumShape Triangular Trapezoid Quadrangular%Female 14.8 74.1 11.1Male 9.1 79.5 11.4BodyShape O-shape Longitudinal oval Flat%Female 12.5 75 12.5Male 7 79 14Standardization according to shape suggests that the-re is one standard sternum shape present in more than2/3 of analysed samples of both sexes. The remainingthird of samples represent extreme variants of the stan-dard shape, diverging from the standard shape values formore than one standard deviation. However, their inci-dence is relatively rare. This result is expected consider-ing biomechanical movements and anatomical location ofthe sternum that is exposed to constant movements inthe process of respiration17,21. The thorax shape of atruncated cone and continuous inspiration/ expirationmovements set conditions for the longitudinal oval ster-num shape, which is named »standard sternum«. All theanalysed parameters lead to conclusion that there is onestandard sternum shape with relatively rare variationsthat form a group of atypical sternum shapes, which rep-resent modifications of the standard shape.Determining the standard dimensions of female andmale sternum and distinguishing typical from atypicalsternum shape may help in standardization of studies in-vestigating qualities of various kinds of sutures and ma-terials used in median sternotomy performed on biologi-cal material. Results of morphometric analysis presentfoundation for further research of biomechanical fea-tures of the sternum. The obtained data may also help inefficient planning of operative interventions and serve asadditional information in assessment of sternum suturedehiscence risk22.AcknowledgementsThis work was supported by the Ministry of Science ofthe Republic of Croatia (Grant No. 0219011).R E F E R E N C E S1. CHENG, W., D. E. CAMERON, K. E. WARDEN, J. D. FOUGER, V.L. GOTT, Ann. Thorac. 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ISAKOVI], Coll Antropol., 28 (2004) 701. — 12.SELTHOFER, R: Problem of structure and strength of the sternum aftercardiac surgery median sternotomy and suture. Ph. D. Thesis. In Croat.(School of Medicine, University »J. J. Strossmayer«, Osijek, 2005). — 13.BOOKSTEIN, F. L., D. E. SLICE, P. H. GUNZ, P. H. MITTEROECKER,Coll. Antropol., 28 (2004) 121. — 14. RUDAN, I., T. [KARI]-JURI], N.SMOLEJ-NARAN^I], B. JANI]IJEVI], D. RUDAN, I. MARTINOVI]KLARI], L. BARA], M. PERI^I], R. GALI], M. LETHBRIDGE-^EJ-KU, P. RUDAN, Coll. Antropol., 28 (2004) 585. — 15. KLARI], I. M., F.LOVA[I], B. BUDISELI], T. [KARI]-JURI], L. SZIROVICZA, A. CHA-VENTRE, Coll. Antropol., 23 (1999) 91. — 16. LEK[AN, I., M. MARCIK-I], V. NIKOLI], R. RADI], R. SELTHOFER, Coll. Antropol., 29 (2005)237. — 17. KRMPOTI]-NEMANI], J.: Anatomija ~ovjeka. In Croat. (Me-dicinska naklada, Zagreb, 1993). — 18. ZACHARIAS, A., R. H. HABIB,Chest, 110 (1996) 1173. — 19. BASKETT, R. J., C. E. MACDOUGALL, D.B. ROSS, Ann. Thorac. Surg., 67 (1999) 462. — 20. BREYER, R., S. MIL-LS, A. HUDSPETH, F. JONSTON, A. CORDELL, Ann. Thorac. Surg., 37(1984) 412. — 21. NIKOLI], V., M. HUDEC: Principi i elementi biome-hanike. In Croat. ([kolska knjiga, Zagreb, 1988). — 22. RUDE@, I.: Clini-cal and biomechanic properties of new method for sternum closure aftermedian sternotomy. Ph. D. Thesis. In Croat. (School of Medicine, Univer-sity »J. J. Strossmayer«, Osijek, 2005).R. SelthoferDepartment of Anatomy, Faculty of Medicine, University »J. J. Strossmayer«, Huttlerova 4, 31000 Osijek, Croatiae-mail: selthofer.robert@kbo.hrR. Selthofer et al.: Morphometric Analysis of the Sternum, Coll. Antropol. 30 (2006) 1: 43–4746Fig. 2. Types of sternum shapes.MORFOMETRIJSKA ANALIZA PRSNE KOSTIS A @ E T A KSternum ima veliko klini~ko zna~enje s obzirom da medijana sternotomija predstavlja naj~e{}i kirur{ki pristup ukardijalnoj kirurgiji. Cilj rada je bio kompleksnom morfometrijskom analizom tipizirati prsnu kost po veli~ini, obliku ispolu te na osnovi takve analize dobiti dimenzije standardnog sternuma. Istra`ivanje je provedeno na 55 mu{kih i 35`enskih sternuma prosje~ne dobi 65 godina. Provedena je kompleksna morfometrijska analiza {irina, duljina i debljinaprsne kosti po definiranim segmentima koji su odre|eni prema rebrenim urezima. Rezultati pokazuju da postoji jedin-stven op}i plan gra|e prsne kosti neovisan o spolu. Dobivene su vrijednosti standardnog `enskog i mu{kog sternuma.Tipizacijom sternuma po obliku utvr|eno je da neovisno o spolu dvije tre}ine uzoraka ima standardan oblik.R. Selthofer et al.: Morphometric Analysis of the Sternum, Coll. Antropol. 30 (2006) 1: 43–4747

Morphometric Analysis of the Sternum

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