Forensic Science Znternational, 50 (1991) l-14 Elsevier Scientific Publishers Ireland Ltd.
STUDYONTHEMICROSTRUCTURESOFSKULLFRACTURE
ZUO ZHI-JIN and ZHLJ JIA-ZHEN Department of Forensic Pathology, Sun Yat-Sen University of Medical Sciences, Guangzhou (China) (Received April 25th, 1989) (Accepted August 22nd, 1989)
Summary The authors observed the edges of skull fractures under the scanning electron microscope. Many microfractures can be found along the main fracture lines. The width of the microfractures varies from 5 to 100 pm. They may be located either in the external compact bone or between the outer compact bone and diplije, or in the diplbe. Those within the dipl6e form transverse, longitudinal or spiral fractures of bony trabeculae. Collagenous fibre bunches in the bony matrix may be divided or broken and the different layers of collagenous fibre may be separated. The blood vessels inside the skull may be crosscut or longitudinally torn by the fracture lines. Sometimes the torn blood vessels may be drawn out of the Haversian canals. In antemortem fractures, the fibrin networks and red blood cells can be easily found in the depths of those cracks. The possible mechanism of formation of the microfractures and the possibility of differentiation between ante- and post-mortem fractures are discussed. Key words: Scanning electron microscope;
Skull fracture;
Microfracture;
Fibrin network
Introduction The skull fracture is one of the most commonly seen mechanical injuries. Many studies have been performed to explain the fracture deformation of skull en masse and the mechanical properties of tiny bone cubes. No report on this aspect using scanning electron microscope was found. Besides, the estimation of the tirntb (11’ bone trauma is still a contraversial problem. We observed the edges of skull fracture under the scanning electron microscope (SEM) in order to determine the submicroscopic morphologic characteristics of skull fractures, aiming at elucidating the mechanism of fractures and differentiating ante- from post-mortem fractures. Materials and Methods (1) An autopsied adult skull was taken and experimental complex fractures were made on it with a stainless steel hammer. The edge of the skull fractures were observed under SEM. (2) Heads of two anaesthetised dogs (weighing 10.5 and 14 kg) were struck by an iron hammer in order to treat comminuted fractures and head injuries. The edges of skull fracture were observed after the dogs were sacrificed. 0379-0738/91/$03.50 0 1991 Elsevier Scientific Publishers Printed and Published in Ireland
Ireland Ltd.
(3) The skull of a fallen adult victim with complex and comminuted fractures was observed also under SEM. The samples were put under a stereo microscope in order to clean the blood clots on the fracture edges with 0.9% saline solution. The samples were then fixed in 10% formalin for 72 h, dehydrated in a series of alcohol and degreased by ether. Finally, they were immersed in acetic-iso-amylester overnight. All samples were dryed with HITACHI HCP-2 Critical Point Dryer for 5 min, critical temperature 15-4O”C, air pressure 60 - 120 kg/cm, then coated in GIKO IB-5 Ion Coater with platinum-plating, 12 min X2, vacuum 0.1 Torr. Finally, the samples were observed under HITACHI S450 scanning electron microscope and photographed. Results The outer part of the external lamina of the skull is formed by many fibrous bone layers. The thickness of this part varies in different locations, and the number of layers also varies in different areas ranging from 10 to 40. Some blood vessels can be found in the inner part of external compact bone. The bone cell cavities are spindle-shaped with long axis parallel to the direction of bony lamellae. Beneath the membranous bone layers are the Haversian systems. The shape of Haversian systems of the skull also varies; they may be triangular, polyangular or ovoid and
Fig. 1. A microfracture
in the external
compact bone (human skull).
3
they inlay each other. The blood vessels travel inside the Haversian canals. Sometimes there may be two blood vessels in one canal. The bone trabeculae in the dipliie are mainly formed by fibrous bone layers. They travel spirally and obliquely round the whole of diplde. The holes in the external layer of dipliie are larger than those in the internal layer while the trabeculae in the external layer are thicker. The internal compact bones have the same structure as the external ones, but thinner. The number of fibrous bone layers usually exceeds ten. In the thinner area of skull the thickness of diploe decreases first. The external and internal compact bone can merge into a single piece and the number of bony layers also decreases. Many microfractures can be found along the main fracture lines and they extend into the surrounding bony tissue. There are cracked bone tissues beside the microfractures. These microfractures can be classified into three kinds: (1) The microfractures inside the external compact bone. They pass through the external lamina obliquely and may also be limited between some layers of the external lamina. The extension of microfracture is parallel to the bone layers or slightly inclined. These fracture lines are relatively smooth and the width of them varies from 5 to 100 pm. They are formed by separation of bony layers or oblique cracks (Fig. 1).
Fig. 2. The microfractures bone (human skull).
between the outer compact bone and diplije and in the external compact
Fig. 3. The microfractures within the dipliie forming transverse, bony trabeculae (human skull). Fig. 4. A trabecula split longitudinally
(human skull).
longitudinal or spiral fractures
of
5
(2) The microfracture between the outer compact bone and dipliie. The cracking lines are wider and rough. Bony tissues of outer lamina and dipliie close to the fracture lines are crushed. The outer lamina may become separated from the diplde. These microfractures may be present simultaneously with those inside the outer compact bone (Fig. 2). (3) The microfracture of trabeculae of dipliie. The fracture lines are irregular, vary greatly in width, location and direction. The diploe are crushed. According to their tracks, the fractures can be divided into three different kinds: (1) The transverse fractures of bony trabeculae. (2) The spiral fractures of bony trabeculae (Fig. 3). (3) The longitudinal fracture of the trabeculae (Fig. 4). High power view (x 2000 - 2500) revealed that collagenous fibres are embedded in the bony matrix in bunches. The fibre bunches are in the same stratum, run parallel1 with each other and diverge in different strata. In case of fracture, the fibre bunches may be divided or broken and the layers of collagenous fibres may be separated. The bone matrix is crushed (Fig. 5). The Haversian system of the skull differs from that in the long bone. The distribution and arrangement of blood vessels inside the external and internal laminae are weblike and ramified. The fracture lines can split Haversian canals transversely, longitudinally and obliquely. When the bony canal is transversely cut, the end of broken canal may be elevated or depressed. The elevated ends look like volcanoes (Fig. 6). The appearances of blood vessel injuries are polymorphic. Sometimes the blood vessel is torn off completely and only the print of blood vessel can be found (Fig. 7). The blood vessels can also be torn longitudinally. The wall of the blood vessel and a piece of bone can be torn off at the same time (Figs. 8 and 9). Furthermore, the torn blood vessels can be drawn out of the Haversian canal and appears like a ribbon. The nerve fibres may accompany the drawn blood vessels (Figs. 10 and 11). The blood vessels inside the skull may be crosscut. The microfractures can destroy the blood vessels mainly along the longitudinal direction (Fig. 12). In antemortem fracture, as a result of hemorrhage, there are not only blood clots on the edge of the broken skull, but also hemorrhage into the microfractures. The fibrin networks and red blood cells which stick together can be easily found in the depths of these cracks (Figs. 13 and 14). Red blood cells can be pushed into the depth of crushed bony tissues. Sometimes in the microfracture fibrin networks plus blood cells can be seen nearby a torn blood vessel. On the contrary, in postmortem fractures, although the edge of fractured skull shows cracks and microfractures, no fibrin networks and red blood cells can be found. Discussion When the skull is crushed by an external force, the elastic region of its stressstrain curve is not linear. This phenomenon explains that the micromechanical property of the skull is not of linearly elastic behavior, i.e. the deformation and yielding of the skull can be expected even in the elastic region. It is caused by debonding of bone units and microfractures on the edges of broken skull. What we found is correspondent with the mechanical features of the skull.
x2000 (dog skull).
canal looks like a volcano. x500 (human skull).
Fig. 5. The collagenous fibre bunches are divided and their layers are separated.
Fig. 6. The broken end of a Haversian
Fig. ‘7. The tracks of blood vessels found on the fracture
Fig. 8. A blood vessel is torn longitudinally.
surface (human skull).
x800 (dog skull).
Fig. 9. The wall of a blood vessel and a piece of bone torn off. x300 (human skull).
The studies carried out by Tokuo Fujita and Chen Shixian indicate respectively that dipliie and bone trabeculae break first as a result of perpendicular impact against the skull; with the increasing of stress, the compact bone laminae will break eventually. Our findings suggest that the trabeculae of dipliie break first, then the junctional zone between external compact bone and the diplbe breaks, then the external compact bone breaks. Microfracture in the internal compact bone is rarely observed. Under the scanning electron microscope, we found that fracture is the destruction of bone layers, that is, the disruption of bone units. The microfractures divide collagenous fibrous bony layers and separate bone fibre bunches. The study of Zhai Yunchang et al. revealed that there are many blood vessels of different diameters forming a network inside the external and internal com-
Fig. 12. A blood vessel torn by microfracture
of the bone. x2000 (dog sk ull).
pact bone. The vessels form branches and ultimately connect with vascular nets of diploe. A similar result has been obtained by us in a perfusion study on the dog skull which will be published in another article. So, it seems that the fractures always and primarily occur in the areas where the blood vessels merge and there are more holes in the bone (Fig. 15). In antemortem injuries of bone, as a result of tearing of blood vessels, the blood cells penetrate into the microfractures. In almost all cases of antemortem fractures we find there are red blood cells and fibrin networks in the microfractures, even in the deep parts. There is no similar finding in the postmortem fractures. This offers the possibility of distinguishing antemortem from postmortem fractures by the finding of fibrin nets and red blood cells in the microfractures.
Fig. 13. (a) The microfractures x 2000 (dog skull).
(dog skull). (b) High power view of (a) shows the fibrin networks and red blood cells in the depths of the microfracture.
12
13
Fig. 15. A fracture
line splitting the blood vessel longitudinally.
x 100 (human skull).
References Mikio Kawase, Physicodynamic studies on the bone fracture impact test. Jup. J. Leg. Med., 19 (1965) 284 - 299. Tokuo Fujita, A basic study of skull fracture-A material-mechanical study using tiny cubes and photoelastic experiment. Jup. J. Leg. Med., 33 (1979) 210-230. Chen Shixian, F’orensic osteology, Qunzhong Publishing House, Beijing, 1933, pp. 11- 31. E.L. Radin, R.M. Rose, S.R. Simon and IL. Paul, Practical Biomechanicsfor theOrthopedic Surgeon, John Wiley & Sons, 1979. Zhai Yunchang, Sun Shoucheng, Chen Yongxiang, Zhang Wencui and Li Dajie, Clinic significance of the structure of the skulls and their vascular distribution. Chinese J. Neurosurg., 1 (1985) 171- 174. Z. Lisowski and 2. Marek, Hyperpigmentation in the long bones of lower limbs as a basic for vehicle identification and traffic accident recontruction. Forensic Sci. Znt., 20 (1982) 251- 255.
14 7
8
9
10 11 12 13 14
Z. Lisowski, E. Baran and Z. Marek, Traumadiagnostik durch Untersuchung ungebrochener Knochen. Arch. F. Krim., 167 (1981) llO- 116. E. Boehm, Three-diamentionai structure of wound surfaces contribution to the study of local vitai reaction and the determination of the age of wounds. In: Scanning Electron Microscope. IITRI, Chicago, 1975, pp. 571. J. Raekahio, Timing of the wound, In: C.G. Tedeschi et al. (Eds.), Forensic medicine - a study in trauma and ewironmental hazards, Vol. 1, Saunders, Philadelphia, 1977, p. 22. F. Takaba, Experimental study on the vital reaction in skin wound. Jap. J. Leg. Med., 32 (1979) 333 - 340. E. B6ehm and K.H. Hochkirchen, Zur uhrsstruktur vitaler, postmortaler und autolysierter gerinnsel. Forensic Sci. Znt., 21 (1983) 117- 127. E. B&hm, Strukturierende Prinsipien H&no&at&her Prozesse. Forensic Sci. Znt.,33 (1987) 7 - 22. Lu Junbao and Zhu J&hen, Inference of ante- and post-mortem wound by observing fibrin under scanning electron microscope. J. Forensic Techl., (1984) 11. Xu Xiaohu and Zhu Jiazhen, Differentiation of ante- and post-mortem bruise by scanning electron microscope. Acad. J. Sun YatSen Univ. Med. Sk, 7 (1986) 42-45.
STUDYONTHEMICROSTRUCTURESOFSKULLFRACTURE
ZUO ZHI-JIN and ZHLJ JIA-ZHEN Department of Forensic Pathology, Sun Yat-Sen University of Medical Sciences, Guangzhou (China) (Received April 25th, 1989) (Accepted August 22nd, 1989)
Summary The authors observed the edges of skull fractures under the scanning electron microscope. Many microfractures can be found along the main fracture lines. The width of the microfractures varies from 5 to 100 pm. They may be located either in the external compact bone or between the outer compact bone and diplije, or in the diplbe. Those within the dipl6e form transverse, longitudinal or spiral fractures of bony trabeculae. Collagenous fibre bunches in the bony matrix may be divided or broken and the different layers of collagenous fibre may be separated. The blood vessels inside the skull may be crosscut or longitudinally torn by the fracture lines. Sometimes the torn blood vessels may be drawn out of the Haversian canals. In antemortem fractures, the fibrin networks and red blood cells can be easily found in the depths of those cracks. The possible mechanism of formation of the microfractures and the possibility of differentiation between ante- and post-mortem fractures are discussed. Key words: Scanning electron microscope;
Skull fracture;
Microfracture;
Fibrin network
Introduction The skull fracture is one of the most commonly seen mechanical injuries. Many studies have been performed to explain the fracture deformation of skull en masse and the mechanical properties of tiny bone cubes. No report on this aspect using scanning electron microscope was found. Besides, the estimation of the tirntb (11’ bone trauma is still a contraversial problem. We observed the edges of skull fracture under the scanning electron microscope (SEM) in order to determine the submicroscopic morphologic characteristics of skull fractures, aiming at elucidating the mechanism of fractures and differentiating ante- from post-mortem fractures. Materials and Methods (1) An autopsied adult skull was taken and experimental complex fractures were made on it with a stainless steel hammer. The edge of the skull fractures were observed under SEM. (2) Heads of two anaesthetised dogs (weighing 10.5 and 14 kg) were struck by an iron hammer in order to treat comminuted fractures and head injuries. The edges of skull fracture were observed after the dogs were sacrificed. 0379-0738/91/$03.50 0 1991 Elsevier Scientific Publishers Printed and Published in Ireland
Ireland Ltd.
(3) The skull of a fallen adult victim with complex and comminuted fractures was observed also under SEM. The samples were put under a stereo microscope in order to clean the blood clots on the fracture edges with 0.9% saline solution. The samples were then fixed in 10% formalin for 72 h, dehydrated in a series of alcohol and degreased by ether. Finally, they were immersed in acetic-iso-amylester overnight. All samples were dryed with HITACHI HCP-2 Critical Point Dryer for 5 min, critical temperature 15-4O”C, air pressure 60 - 120 kg/cm, then coated in GIKO IB-5 Ion Coater with platinum-plating, 12 min X2, vacuum 0.1 Torr. Finally, the samples were observed under HITACHI S450 scanning electron microscope and photographed. Results The outer part of the external lamina of the skull is formed by many fibrous bone layers. The thickness of this part varies in different locations, and the number of layers also varies in different areas ranging from 10 to 40. Some blood vessels can be found in the inner part of external compact bone. The bone cell cavities are spindle-shaped with long axis parallel to the direction of bony lamellae. Beneath the membranous bone layers are the Haversian systems. The shape of Haversian systems of the skull also varies; they may be triangular, polyangular or ovoid and
Fig. 1. A microfracture
in the external
compact bone (human skull).
3
they inlay each other. The blood vessels travel inside the Haversian canals. Sometimes there may be two blood vessels in one canal. The bone trabeculae in the dipliie are mainly formed by fibrous bone layers. They travel spirally and obliquely round the whole of diplde. The holes in the external layer of dipliie are larger than those in the internal layer while the trabeculae in the external layer are thicker. The internal compact bones have the same structure as the external ones, but thinner. The number of fibrous bone layers usually exceeds ten. In the thinner area of skull the thickness of diploe decreases first. The external and internal compact bone can merge into a single piece and the number of bony layers also decreases. Many microfractures can be found along the main fracture lines and they extend into the surrounding bony tissue. There are cracked bone tissues beside the microfractures. These microfractures can be classified into three kinds: (1) The microfractures inside the external compact bone. They pass through the external lamina obliquely and may also be limited between some layers of the external lamina. The extension of microfracture is parallel to the bone layers or slightly inclined. These fracture lines are relatively smooth and the width of them varies from 5 to 100 pm. They are formed by separation of bony layers or oblique cracks (Fig. 1).
Fig. 2. The microfractures bone (human skull).
between the outer compact bone and diplije and in the external compact
Fig. 3. The microfractures within the dipliie forming transverse, bony trabeculae (human skull). Fig. 4. A trabecula split longitudinally
(human skull).
longitudinal or spiral fractures
of
5
(2) The microfracture between the outer compact bone and dipliie. The cracking lines are wider and rough. Bony tissues of outer lamina and dipliie close to the fracture lines are crushed. The outer lamina may become separated from the diplde. These microfractures may be present simultaneously with those inside the outer compact bone (Fig. 2). (3) The microfracture of trabeculae of dipliie. The fracture lines are irregular, vary greatly in width, location and direction. The diploe are crushed. According to their tracks, the fractures can be divided into three different kinds: (1) The transverse fractures of bony trabeculae. (2) The spiral fractures of bony trabeculae (Fig. 3). (3) The longitudinal fracture of the trabeculae (Fig. 4). High power view (x 2000 - 2500) revealed that collagenous fibres are embedded in the bony matrix in bunches. The fibre bunches are in the same stratum, run parallel1 with each other and diverge in different strata. In case of fracture, the fibre bunches may be divided or broken and the layers of collagenous fibres may be separated. The bone matrix is crushed (Fig. 5). The Haversian system of the skull differs from that in the long bone. The distribution and arrangement of blood vessels inside the external and internal laminae are weblike and ramified. The fracture lines can split Haversian canals transversely, longitudinally and obliquely. When the bony canal is transversely cut, the end of broken canal may be elevated or depressed. The elevated ends look like volcanoes (Fig. 6). The appearances of blood vessel injuries are polymorphic. Sometimes the blood vessel is torn off completely and only the print of blood vessel can be found (Fig. 7). The blood vessels can also be torn longitudinally. The wall of the blood vessel and a piece of bone can be torn off at the same time (Figs. 8 and 9). Furthermore, the torn blood vessels can be drawn out of the Haversian canal and appears like a ribbon. The nerve fibres may accompany the drawn blood vessels (Figs. 10 and 11). The blood vessels inside the skull may be crosscut. The microfractures can destroy the blood vessels mainly along the longitudinal direction (Fig. 12). In antemortem fracture, as a result of hemorrhage, there are not only blood clots on the edge of the broken skull, but also hemorrhage into the microfractures. The fibrin networks and red blood cells which stick together can be easily found in the depths of these cracks (Figs. 13 and 14). Red blood cells can be pushed into the depth of crushed bony tissues. Sometimes in the microfracture fibrin networks plus blood cells can be seen nearby a torn blood vessel. On the contrary, in postmortem fractures, although the edge of fractured skull shows cracks and microfractures, no fibrin networks and red blood cells can be found. Discussion When the skull is crushed by an external force, the elastic region of its stressstrain curve is not linear. This phenomenon explains that the micromechanical property of the skull is not of linearly elastic behavior, i.e. the deformation and yielding of the skull can be expected even in the elastic region. It is caused by debonding of bone units and microfractures on the edges of broken skull. What we found is correspondent with the mechanical features of the skull.
x2000 (dog skull).
canal looks like a volcano. x500 (human skull).
Fig. 5. The collagenous fibre bunches are divided and their layers are separated.
Fig. 6. The broken end of a Haversian
Fig. ‘7. The tracks of blood vessels found on the fracture
Fig. 8. A blood vessel is torn longitudinally.
surface (human skull).
x800 (dog skull).
Fig. 9. The wall of a blood vessel and a piece of bone torn off. x300 (human skull).
The studies carried out by Tokuo Fujita and Chen Shixian indicate respectively that dipliie and bone trabeculae break first as a result of perpendicular impact against the skull; with the increasing of stress, the compact bone laminae will break eventually. Our findings suggest that the trabeculae of dipliie break first, then the junctional zone between external compact bone and the diplbe breaks, then the external compact bone breaks. Microfracture in the internal compact bone is rarely observed. Under the scanning electron microscope, we found that fracture is the destruction of bone layers, that is, the disruption of bone units. The microfractures divide collagenous fibrous bony layers and separate bone fibre bunches. The study of Zhai Yunchang et al. revealed that there are many blood vessels of different diameters forming a network inside the external and internal com-
Fig. 12. A blood vessel torn by microfracture
of the bone. x2000 (dog sk ull).
pact bone. The vessels form branches and ultimately connect with vascular nets of diploe. A similar result has been obtained by us in a perfusion study on the dog skull which will be published in another article. So, it seems that the fractures always and primarily occur in the areas where the blood vessels merge and there are more holes in the bone (Fig. 15). In antemortem injuries of bone, as a result of tearing of blood vessels, the blood cells penetrate into the microfractures. In almost all cases of antemortem fractures we find there are red blood cells and fibrin networks in the microfractures, even in the deep parts. There is no similar finding in the postmortem fractures. This offers the possibility of distinguishing antemortem from postmortem fractures by the finding of fibrin nets and red blood cells in the microfractures.
Fig. 13. (a) The microfractures x 2000 (dog skull).
(dog skull). (b) High power view of (a) shows the fibrin networks and red blood cells in the depths of the microfracture.
12
13
Fig. 15. A fracture
line splitting the blood vessel longitudinally.
x 100 (human skull).
References Mikio Kawase, Physicodynamic studies on the bone fracture impact test. Jup. J. Leg. Med., 19 (1965) 284 - 299. Tokuo Fujita, A basic study of skull fracture-A material-mechanical study using tiny cubes and photoelastic experiment. Jup. J. Leg. Med., 33 (1979) 210-230. Chen Shixian, F’orensic osteology, Qunzhong Publishing House, Beijing, 1933, pp. 11- 31. E.L. Radin, R.M. Rose, S.R. Simon and IL. Paul, Practical Biomechanicsfor theOrthopedic Surgeon, John Wiley & Sons, 1979. Zhai Yunchang, Sun Shoucheng, Chen Yongxiang, Zhang Wencui and Li Dajie, Clinic significance of the structure of the skulls and their vascular distribution. Chinese J. Neurosurg., 1 (1985) 171- 174. Z. Lisowski and 2. Marek, Hyperpigmentation in the long bones of lower limbs as a basic for vehicle identification and traffic accident recontruction. Forensic Sci. Znt., 20 (1982) 251- 255.
14 7
8
9
10 11 12 13 14
Z. Lisowski, E. Baran and Z. Marek, Traumadiagnostik durch Untersuchung ungebrochener Knochen. Arch. F. Krim., 167 (1981) llO- 116. E. Boehm, Three-diamentionai structure of wound surfaces contribution to the study of local vitai reaction and the determination of the age of wounds. In: Scanning Electron Microscope. IITRI, Chicago, 1975, pp. 571. J. Raekahio, Timing of the wound, In: C.G. Tedeschi et al. (Eds.), Forensic medicine - a study in trauma and ewironmental hazards, Vol. 1, Saunders, Philadelphia, 1977, p. 22. F. Takaba, Experimental study on the vital reaction in skin wound. Jap. J. Leg. Med., 32 (1979) 333 - 340. E. B6ehm and K.H. Hochkirchen, Zur uhrsstruktur vitaler, postmortaler und autolysierter gerinnsel. Forensic Sci. Znt., 21 (1983) 117- 127. E. B&hm, Strukturierende Prinsipien H&no&at&her Prozesse. Forensic Sci. Znt.,33 (1987) 7 - 22. Lu Junbao and Zhu J&hen, Inference of ante- and post-mortem wound by observing fibrin under scanning electron microscope. J. Forensic Techl., (1984) 11. Xu Xiaohu and Zhu Jiazhen, Differentiation of ante- and post-mortem bruise by scanning electron microscope. Acad. J. Sun YatSen Univ. Med. Sk, 7 (1986) 42-45.
