Dimensional Analysis of the Parietal Bone in Areas of Surgical Interest and Relationship Between Parietal Thickness and Cephalic Index

J Oral Maxillofac Surg 69:2930-2935, 2011 Dimensional Analysis of the Parietal Bone in Areas of Surgical Interest and Relationship Between Parietal Thickness and Cephalic Index Atson Carlos de Souza Fernandes, DDS, PhD,* Antonio Irineu Trindade Neto, DDS,† André Carlos de Freitas, DDS, PhD,‡ and Márcio de Moraes, DDS, PhD§ Purpose: The aim of this study was to determine the thickness of the parietal bone in bone graft donor sites and to study the relationship between parietal bone thickness and gender or cephalic index. Materials and Methods: We studied 300 parietal bones from 150 human skulls (84 male and 66 female) from individuals aged 18 to 60 years at the time of death. On each parietal bone, 9 areas were drawn by use of reference anatomic landmarks (bregma, lambda, asterion, and pterion), and bone thickness was determined in the areas adjoining the sagittal suture—superior-anterior (Sa), superiormedial (Sm), and superior-posterior (Sp). Results: Mean thickness measurements ranged from 2.30 to 11.25 mm in the Sa area, from 3.08 to 13.32 mm in the Sm area, and from 2.88 to 12.26 in the Sp area. Smaller mean measurements were observed in the Sa area, with the smallest mean thickness being found in brachycephalic female specimens. The largest mean thickness was also found in female specimens in the Sm area. Statistically significant differences between genders were found only in the Sa area in dolichocephalic and mesocephalic specimens. Conclusion: Although the best bone graft donor site surgically is different in individuals of different genders and with different cephalic indexes, our findings suggest that harvesting from the anterosuperior area of the parietal bone should not be performed. © 2011 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 69:2930-2935, 2011 Autogenous bone graft obtained from the skull has been used in facial surgical reconstruction procedures such as that of the dorsum of the nose and in patients with esthetic problems caused by tumor growth.1-3 Autogenous bone graft has also been successfully used in reconstructions of the alveolar process in both the maxilla and mandible, as well as in procedures involving osseointegrated dental implants.4-6 Furthermore, several studies have shown that membranous bone grafts survive better than en- dochondral bone in terms of shape and volume after grafting.7-12 Another advantage of using skull graft is that it is esthetic because surgical signs become not as readily noticeable. In addition, the rate of healing problems in the skull is reported to be much lower compared with other donor areas, and postoperative pain complaints are rare.13,14 In the skull, bone graft is more frequently harvested from the parietal bone,1,9,15-17 and the harvesting *Professor, State University of Bahia/Bahiana School of Medicine and Public Health, Bahia, Brazil. †Resident, Federal University of Bahia-Santo Antônio Hospital, Bahia, Brazil. ‡Professor, Federal University of Bahia, Bahia, Brazil. §Professor, State University of Campinas, São Paulo, Brazil. Address correspondence and reprint requests to Dr Fernandes: State University of Bahia/Bahiana School of Medicine and Public Health, Rua Silveira Martins, 2555, Cabula, Salvador, Bahia, Brazil; e-mail: atson@uneb.br © 2011 American Association of Oral and Maxillofacial Surgeons 0278-2391/11/6911-0053$36.00/0 doi:10.1016/j.joms.2011.02.026 2930 2931 DE SOUZA FERNANDES ET AL and Cannella and Hopkins22 refer to the portion close to the sagittal suture in all the anterior, medial, and posterior thirds of the parietal bone as the donor site of choice. The aim of this study was to determine the thickness of the parietal bone, according to gender and cranial index of the samples studied, in an attempt to improve guidance as to the harvesting of calvarial bone graft. Materials and Methods This study was performed on 150 dried human skulls from 85 male and 66 female individuals aged 18 to 60 years at the time of death. MORPHOMETRIC ANALYSIS Drawing straight lines connecting craniometric landmarks, we divided the parietal bone into 9 portions. The 3 portions within 2 cm approximately from the sagittal suture were defined as areas of interest for this study, because bone graft harvesting is most frequently performed in such portions of the parietal bone. These portions were identified as superior-anterior (Sa), superior-middle (Sm), and superior-posterior (Sp). Straight lines connecting opposite corners of each portion were drawn. The points determined by the intersection of each pair of straight lines were elected as study points where the thickness of the parietal bone was taken (Fig 1). Three measurements were thus performed for each parietal bone studied. FIGURE 1. Points (Sa, Sm, and Sp) selected to measure thickness of parietal bone. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. technique of choice consists of obtaining a blade of the outer cortical bone (outer table), thus saving the majority of the cancellous bone layer in the harvest site.18,19 Complications resulting from harvesting of the outer table include epidural abscess, meningitis, hemorrhage from the sagittal sinus, rupture of the dura mater, and hematoma.9,20 Sullivan and Smith21 report bone graft harvesting from the parietal bone performed 3 cm away from the sagittal suture and 2 cm posteriorly to the coronal suture as the most frequent area. In contrast, Edwards and Ousterhout13 advocate the area located in the medial and posterior thirds of the parietal bone, close to the sagittal suture, as a donor site, whereas Tessier7 THICKNESS MEASUREMENT After we determined the thickness study points and the cephalic index (CI), the top part of the skull was removed to carry out parietal bone thickness determinations of Sa, Sm, and Sp. These were obtained by use of a precision electronic thickness gauge (model EOD 2050; Oditronic Digital, Kroeplin, Germany) with minimum determination of 0.02 mm. STATISTICAL ANALYSIS Nonparametric tests were used in this study. The Wilcoxon test was used to compare paired data (Sa, Sm, Sp, gender, and CI) from the left and right side. Table 1. MEAN, MINIMUM, AND MAXIMUM THICKNESS IN SA THIRD OF RIGHT AND LEFT PARIETAL BONE IN MALE AND FEMALE DOLICHOCEPHALIC SKULLS AND STATISTICAL RESULTS Side Gender n Mean (mm) Minimum (mm) Maximum (mm) R L R L M M F F 34 34 16 16 6.27 5.87 5.42 5.42 3.94 2.30 3.12 3.38 11.25 9.47 8.06 8.39 Abbreviations: *, significant; NS, not significant. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. Wilcoxon Test Zcalc ⫽ ⫺2.548* Zcalc ⫽ ⫺0.207 (NS) 2932 DIMENSIONAL ANALYSIS OF PARIETAL BONE Table 2. MEAN, MINIMUM, AND MAXIMUM THICKNESS IN SP THIRD OF RIGHT AND LEFT PARIETAL BONE IN MALE AND FEMALE MESOCEPHALIC SKULLS AND STATISTICAL RESULTS Side Gender n Mean (mm) Minimum (mm) Maximum (mm) Wilcoxon Test R L R L M M F F 29 29 32 32 6.88 7.12 6.69 7.06 4.40 4.16 4.74 5.23 9.26 9.80 9.88 11.36 Zcalc ⫽ ⫺2.162* Zcalc ⫽ ⫺3.361* Abbreviation: *, significant. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. Table 3. MEAN, MINIMUM, AND MAXIMUM THICKNESS IN SA, SM, AND SP THIRDS OF BOTH SIDES IN MALE AND FEMALE DOLICHOCEPHALIC SKULLS AND STATISTICAL RESULTS Parameters Gender n Mean (mm) Minimum (mm) Maximum (mm) Friedman Test Significant Comparison Sa Sm Sp Sa Sm Sp M M M F F F 68 68 68 32 32 32 6.07 7.13 7.12 5.42 6.96 6.67 2.30 3.54 4.82 3.12 4.48 2.88 11.25 11.86 12.26 8.39 9.31 9.00 ␹2calc ⫽ 31.853* Sa ⬍ Sm Sa ⬍ Sp ␹2calc ⫽ 27.701* Sa ⬍ Sm Sa ⬍ Sp Abbreviation: *, significant. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. Table 4. MEAN, MINIMUM, AND MAXIMUM THICKNESS IN SA, SM, AND SP THIRDS OF BOTH SIDES IN MALE AND FEMALE MESOCEPHALIC SKULLS AND STATISTICAL RESULTS Parameters Gender n Mean (mm) Minimum (mm) Maximum (mm) Friedman Test Significant Comparison Sa Sm Sp Sa Sm Sp M M M F F F 58 58 58 64 64 64 5.75 6.98 7.00 5.19 7.40 6.87 2.85 3.08 4.16 2.90 4.96 4.74 9.14 9.50 9.80 9.20 13.32 11.36 ␹2calc ⫽ 28.835* Sa ⬍ Sm Sa ⬍ Sp ␹2calc ⫽ 84.656* Sa ⬍ Sm Sa ⬍ Sp Sm ⬎ Sp Abbreviation: *, significant. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. The Friedman test used to compare Sa, Sm, and Sp referred to the same CI and gender. The Mann-Whitney test was used to compare genders regarding Sa, Sm, Sp, and CI. The Kruskal-Wallis was applied to compare dolichocephalic, mesocephalic, and brachycephalic thickness measurements at Sa, Sm, and Sp. The level of statistical significance was set to 5% (P ⱕ .05) in all 2-tailed tests. Results COMPARISON BETWEEN SIDES Regarding side, statistically significant differences in mean thickness were found for measurements in Sa in dolichocephalic male skulls, with the right side showing greater mean thickness (6.27 mm), and for measurements in Sp in mesocephalic skulls, where larger mean thickness values of 7.12 mm and 7.06 mm were found on the left side of male and female skulls, respectively (Tables 1, 2). COMPARISON BETWEEN SA, SM, AND SP After we compared sides, data referring to opposite sides were pooled to compare thickness in each of the 3 different study portions of the parietal bone. Tables 3, 4, and 5 show statistically significant differences regarding gender in each of the 3 CI groups. COMPARISON BETWEEN GENDERS With the exception of dolichocephalic and mesocephalic Sa measurements, which showed a larger mean thickness rate for male specimens, no statistically significant differences in mean thickness were found with regard to gender (Tables 6-8). COMPARISON BETWEEN CI GROUPS Mean thickness measurements in Sa and Sp were found to be larger in the dolichocephalic group (5.86 mm and 6.97 mm, respectively) and in Sp in the mesocephalic group (6.97 mm) (Table 9). 2933 DE SOUZA FERNANDES ET AL Table 5. MEAN, MINIMUM, AND MAXIMUM THICKNESS IN SA, SM, AND SP THIRDS OF BOTH SIDES IN MALE AND FEMALE BRACHYCEPHALIC SKULLS AND STATISTICAL RESULTS Parameters Gender Sa Sm Sp Sa Sm Sp M M M F F F n 42 42 42 36 36 36 Mean (mm) Minimum (mm) 5.51 7.08 6.27 5.20 6.60 6.61 3.26 4.68 3.74 3.45 4.06 4.60 Maximum (mm) 9.66 11.16 9.84 7.48 9.56 8.70 Friedman Test 2 Significant Comparison ⫽ 30.333* Sa ⬍ Sm Sm ⬎ Sp ␹2calc ⫽ 26.056* Sa ⬍ Sm Sa ⬍ Sp ␹ calc Abbreviation: *, significant. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. Table 6. MEAN THICKNESS IN SA, SM, AND SP THIRDS IN DOLICHOCEPHALIC SKULLS AND STATISTICAL RESULTS BY GENDER Parameters Gender n Mean (mm) Sa Sa Sm Sm Sp Sp M F M F M F 68 32 68 32 68 32 6.07 5.42 7.13 6.96 7.12 6.67 Mann-Whitney Test Significant Comparison Zcalc ⫽ ⫺2.221* Sa in men ⬎ Sa in women Zcalc ⫽ ⫺0.122 (NS) Sm in men ⫽ Sm in women Zcalc ⫽ ⫺0.761 (NS) Sp in men ⫽ Sp in women Abbreviations: *, significant; NS, not significant. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. Table 7. MEAN THICKNESS IN SA, SM, AND SP THIRDS IN MESOCEPHALIC SKULLS AND STATISTICAL RESULTS BY GENDER Parameters Gender n Mean (mm) Sa Sa Sm Sm Sp Sp M F M F M F 58 64 58 64 58 64 5.75 5.19 6.98 7.40 7.00 6.87 Mann-Whitney Test Significant Comparison Zcalc ⫽ ⫺2.615* Sa in men ⬎ Sa in women Zcalc ⫽ ⫺0.515 (NS) Sm in men ⫽ Sm in women Zcalc ⫽ ⫺0.938 (NS) Sp in men ⫽ Sp in women Abbreviations: *, significant; NS, not significant. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. Discussion The way that bone thickness varies throughout the parietal bone is meaningful when the calvaria is clinically harvested, because neurosurgical complications may be diminished when harvesting is conducted from thicker areas.1,2,23 Comparing studies on human skull thickness frequently poses difficulties that are hard to overcome, because the methods these studies use to present their findings and/or select thickness checkpoints can vary greatly. This study addresses sites in the parietal bone that are of surgical interest regarding the harvesting of bone graft. There is a consensus on obtaining bone graft material from the parietal bone close to the sagittal suture. However, the lateral safety margin to prevent injury to the sagittal sinus varies from 1 to 3 cm away from the sagittal suture.2 The recommended site for harvesting bone also varies greatly, starting at the coronal suture and going as far as the area adjoining the occipital bone. Edwards and Ousterhout13 reported the medial and posterior thirds of the parietal bone, close to the sagittal suture, as the most appropriate bone harvesting location, whereas findings from Sullivan and Smith21 suggest the anterior third, 2 cm away from the coronal suture, should be used. In contrast, Tessier7 and Cannella and Hopkins22 report that collecting bone graft material in any of the anterior, middle, or posterior thirds is advisable as long as harvesting is performed close to the sagittal suture. Taking into account the findings reported in the literature, we analyzed the thickness of the parietal bone in points located in the anterior, medial, and posterior thirds of the referred bone (Sa, Sm, and Sp, respectively) running close to the sagittal suture and de- 2934 DIMENSIONAL ANALYSIS OF PARIETAL BONE Table 8. MEAN THICKNESS IN SA, SM, AND SP THIRDS IN BRACHYCEPHALIC SKULLS AND STATISTICAL RESULTS BY GENDER Parameters Gender n Mean (mm) Mann-Whitney Test Significant Comparison Sa Sa Sm Sm Sp Sp M F M F M F 42 36 42 36 42 36 5.51 5.20 7.08 6.60 6.27 6.61 Zcalc ⫽ ⫺0.421 (NS) Sa in men ⫽ Sa in women Zcalc ⫽ ⫺1.473 (NS) Sm in men ⫽ Sm in women Zcalc ⫽ ⫺1.514 (NS) Sp in men ⫽ Sp in women Abbreviation: NS, not significant. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. termined their potential relationship with gender and CI. Our study found a significant relationship between the parietal bone thickness at the points studied and CI, a relationship not yet reported in the literature to our knowledge. In contrast to the findings of Sullivan and Smith,21 our findings show that bone harvesting should be avoided in the Sa site, because this was shown to be the least thick of the 3 sites studied, regardless of gender and CI, thus increasing the risk of full-thickness injury to the parietal bone. Our findings also suggest that for dolichocephalic and mesocephalic patients, whether male or female patients, bone harvesting should be performed in the medial and posterior thirds of the parietal bone. However, in female mesocephalic individuals, the harvesting site of choice should be the medial third, which was shown to be the thickest (7.40 mm). Similar to mesocephalic female individuals, brachycephalic male patients show the largest thickness (7.08 mm) in the medial third (Sm). In the latter individuals, the thickness at Sa and Sp (anterior and posterior thirds, respectively) showed no statistically significant difference. On the other hand, brachycephalic female individuals showed the same parietal thickness distribution pattern as dolichocephalic individuals, where gender does not imply statistically significant differences in thickness. Our findings are similar to a previous study where the sites studied, D2 and E2, which are topographically close to Sa as determined in our study (on the right and left sides), showed the least thickness as compared with the other sites. Adeloye et al,24 comparing genders, reported that white men showed the largest thickness in the parietal bone close to the coronal suture whereas in white women the parietal bone was thickest in the posterior third. These findings were similar to those of Hwang et al19 and Ross et al.25 This study does not report large differences in bone thickness between male and female individuals. However, at Sa, a similar location to that studied by Adeloye et al close to the coronal suture, our findings show that in dolichocephalic and mesocephalic male subjects, the parietal thickness is largest, a determination similar to the previously mentioned authors. Pensler and McCarthy26 reported a larger thickness in men, by 1 to 2 mm, as compared with women. Such an order of difference was not found in our study or in the studies by Adeloye et al24 and Hwang et al.19 This may result from the topographic difference between the point foci in different studies. The largest thicknesses found in the parietal bone by Hwang et al3 and Jung et al23 were 6.67 mm and 7.16 mm, respectively, in the posteromedial portion. Furthermore, both studies found the smallest thick- Table 9. MEAN THICKNESS OF BOTH SIDES AND BOTH GENDERS IN SA, SM, AND SP THIRDS AND STATISTICAL RESULTS BY CI Mean (mm) Significant Comparison Kruskal-Wallis Test CI n Sa Sm Sp Sa Sm Sp Sa Sp Dolichocephalic Mesocephalic Brachycephalic 100 122 78 5.86 5.46 5.37 7.08 7.20 6.86 6.97 6.93 6.43 ␹2calc ⫽ 8.086* ␹2calc ⫽ 2.718 (NS) ␹2calc ⫽ 8.005* D⬎B D⬎M D⬎B M⬎B Abbreviations: D, dolichocephalic; M, mesocephalic; B, brachycephalic. de Souza Fernandes et al. Dimensional Analysis of Parietal Bone. J Oral Maxillofac Surg 2011. DE SOUZA FERNANDES ET AL ness in the superior third of the anterior portion (5.3 mm). Our findings are similar to those of Hwang et al in that we have determined a similar thickness (5.19 mm) at a similar site (Sa). However, our largest measurements were not determined in the posteromedial portion but in the superior-medial portion (7.40 mm and 7.08 mm in mesocephalic and brachycephalic subjects, respectively). Jung et al23 and Pensler and McCarthy26 reported mean thickness measurements of the parietal bone ranging from 5.03 to 7.16 mm and from 6.80 to 7.72 mm, respectively. In contrast, Psillakis et al27 report mean values varying from 4 to 6 mm, a range of measurements below that reported in our study. Regardless of gender and CI, our study observed mean bone thicknesses in the anterior, medial, and posterior thirds of the parietal bone close to the sagittal suture ranging from 2.30 to 11.25 mm, from 3.08 to 13.32 mm, and from 2.88 to 12.26 mm, respectively. Unlike the studies by Pensler and McCarthy26 and Ishizuca,28 our study showed only a few statistically significant differences in thickness values when skull sides were compared. In mesocephalic skulls of male and female individuals, the thickest measurement was determined in the left parietal bone at Sp, a finding similar to that of Hwang et al,3 who reported points A3 and A4 on the left side of the skull. References 1. 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