OSTEOLOGY OF THE SKULL AND VERTE3eeeeeeeeBRAE.pptx

Hematological principles

1. OSTEOLOGY OF THE SKULL AND VERTEBRAE BY :GALIWANGO HENRY AND BAKOWA PAUL MODERATOR :DR KYAMANYA

2. OUTLINE Introduction Embryological development of skull and vertebrae Congenital anomalies New born skull Views of the skull Vertebrae

3. Introductory Summary Skull is 28 separate bones, almost all either paired or with sagittal symmetry. Flat vault bones have two tables/plates of compact bone enclosing a narrow layer of relatively dense cancellous marrow (diploic bone) containing venous structures. Foramina in these bones transmit neurovascular bundles that may be compromised at these sites by pathology or trauma. Skull is divided into the: Neuro-cranium. ie . calvaria and basi -cranium Viscero -cranium. ie . facial bones and their paranasal sinuses The skull articulates with the first cervical vertebra (Atlas), enabling movement at the atlanto -occipital joints.

4. The skull is the most useful source of information in the ; -biological identity( age,sex,ethnic origin) - personal identification of individuals(DNA) Basically the skeletal system is divided into axial skeleton( skull,sternum,ribs and vertebrae) appendicular skeleton(pectoral girdle,pelvic girdle limbs)

5. Vertebral column The vertebral column is made up of five parts with individual vertebrae peculiar to each: cervical, thoracic, lumbar, sacral and coccygeal In the fetus, the column lies flexed in its whole extent , like the letter C. This anterior flexion or concavity is the primary curvature of the column and is retained throughout life in the thoracic, sacral and coccygeal parts After birth secondary extension of the column produces the secondary curvatures with an anterior convexity (i.e. lordosis) in the cervical and lumbar regions

6. General features It consists of a ventral body and a dorsal vertebral or neural arch which enclose between them the vertebral foramen From the neural arch three processes diverge: in the posterior midline, the spinous process (spine) and on either side the transverse processes . That part of the neural arch between spinous process and transverse process is the lamina That part between transverse process and body is the pedicle.

7. Intro’ concluded. Neck has 7 cervical vertebrae, smallest of the movable vertebrae Characterized by: A disproportionately large vertebral canal. Foramen transversarium (may be absent or sometimes duplicated in the 7 th ). Often bifid spinous processes (except 1 st and 7 th ) Atypical cervical vertebrae: 1 st (Atlas), 2 nd (Axis), 7 th (Vertebra prominens ) Hyoid bone lies in the midline at the front of the neck at the level of C-3. Suspended from the styloid processes by stylohyoid ligaments. Gives attachment to the supra- and infra-hyoid groups of muscles.

8. Skull provides attachments for: Craniofacial and oculogyric muscles Muscles acting on the temporomandibular joint Superior constrictor of the pharynx Muscles of the soft palate All but one of the extrinsic muscles of the tongue Muscles of the suboccipital region, and the cranial attachments of trapezius and sternocleidomastoid.

9. Embryology of the skull The initial devt of the skeleton is from the : Lateral plate mesoderm Paraxial mesoderm Neural crest cells

10. Segmentation of the paraxial mesoderm somatpmeres @cranial end and somites @caudal end

11. During 4 th wk somites divide into ventral-medial sclerotomes and dorsal-lateral dermomyotome

12. Therefore:

13. Ossification;the somatomeres , somites,neural crest cells differentiate into loose connective tissue.

14. The loose connective tissue (mesenchyme) forms many cells : Fibroblasts Chondroblasts Osteoblasts These cells favour the ossification of the bones .therefore for the flat bones ( frontal,parietal , temporal bone and occipital bone ) there is laying down of the osteoblasts hence intramembraneous ossification.

15. Therefore during 2 nd month of IUL the elements of the membraneous neurocranium are formed by intramembraneous ossification; 1 st raise down primary ossification centers which spread to form Bony spicules @the periphery.these bony spicules enlarge ,radiate and spread to form the flat bones by apposition of new layers of bone from outside(osteoblasts) and bone resorption from inside(osteoclasts).

16. Newborn Skull At birth, the flat bones of the skull are separated from each other by narrow areas of connective tissue known as sutures. At points where more than two bones meet, sutures are widened into fontanelles . The most prominent of these is the anterior fontanelle, between two parietal and two frontal bones. Functionally, they aid delivery of baby and accommodate rapid brain growth in first 2 years of life In the adult, these sutures (synarthroses) form fibrous immovable joints.

17. Sutures of Newborn Skull

18. Devt of chondrocranium (base of the skull)/cartilaginous bones by endochondral ossification occurs at 3parts.

19. The ossification of the chondrocranium is under the influence of sonic hedgehog signalling pathway. This ossification starts during 2 nd month of IUL but completed at puberty. Takes 24-25 years for the body of sphenoid to fuse with the bassiocciput .

20. Devt of viscera cranium/facial skeleton

21. Periods of the Growth of the Skull The first period (the first 7 years) is characterized by intensive growth, mainly of the posterior part of the skull. The second period (from the age of 7 to the beginning of puberty), and this is the period of relative rest. The third period , from the beginning of puberty (13-16 years of age) to the end of skeletal growth (20-23 years of age), is again one of intensive growth, and during this period growth mainly the anterior part of the skull.

22. Sex Specific Features of the Skull The skull of a man is larger than the skull of a woman in average. The capacity of the skull in man also is greater than in female by approximately 10%. This fact is determined by the sex difference in the body dimensions. The fact that the muscles in female are not as well developed as in man assures to the skull a smooth surface, but in man the roughnesses at the sites of muscle attachment is more pronounced. In female the superciliary arches are less prominent, the forehead is more vertical, and the vertex flatter. All these signs sometimes are not well distinct and cannot serve as reference points in determining the sex of an individual. In approximately 20% of cases the capacity of the female skull is no less than the average capacity of the male skull. The smaller size of the female skull does not signify poorer development of the brain of female but corresponds to the smaller dimensions and proportions of the female body.

23. Congenital anomalies /clinical correlates

24. Take home

25. Stages of dev’t of the vertebrae

26. During the mesenchyme stage 4-6 th wk the mesenchyme appears around the notochord and later undergo condensation. In the chondrification stage 6 th -7 th wk the chondrofication centers appear with in th condensing mesenchyme coz they are to form hyaline cartilage model. The osseous stage takes place in 2stages Primary ossification centre @7 th wk where there is development of the body and transverse processes Then secondary ossification centrs @7-15 yrs . The ossification becomes complete by 25years.and its by endochondrial process.

27. correlates

28. The skull views Norma frontalis Norma verticalis (outer and inner) Norma occipitalis Norma basalis Norma lateralis

29. Norma Frontalis Bones ; frontal bone (1) –forms the upper border or roof of the orbit. -has maxillary process and zygomatic processes Nasal bones(2) Zygomatic bones(2)-has frontal processes and maxillary processes Maxilla-forms the upper jaw and has the frontal processes articulating with the frontal bone and also zygomatic processes which articulate with the zygomatic bones. Has alveolar process forming the alveolar arch and the alveolar ridge is asite fracture line in Le forte I injuries. Mandible;forms the lower jaw

30. The sutures ; Coronal sutures –appear between the frontoal bone and parietal bones Metopic suture –in infant skull.which appears between the two halves of thee frontal bone. It disappears at the age of 2-6yrs.its lower part may persist that can be mistaken to be for fracture of the frontal bone in adults(8%). 3) fronto -nasal suture 4) fronto -zygomatic sutures 5) Internasal sutures

31. Land marks 1)Frontal eminence-the center of ossification of the frontal bone 2) Supercilliary arches(2)-above the orbits and more prominent in males 3)glabella- btn the 2supercilliary arches ,also more prominent in males 4) Nasion ;depression at the frontal nasal suture 5)Nasal septum and anterior nasal spine. 6)Nasal conchae;middle and inferior nasal conchae. 7)Canine eminence-formed by the root of canine teeth and cosmetically contributes to the contour of the lower face

32. The foramina 1) Suraorbital foramen-transmits supraorbital nerve and vessels 2)Infra orbital foramen-transmits infraorbitalnerve and vessels 3) Zygomaticofrontal foramen-transmits the zygomaticofacial nerve and vessels 4)Mental foramen:transmits the mental nerve and vessels

33. Norma Verticalis Externa The bones: frontal bone parietal bones occipital bone Sutures; 1)coronal suture( btn frontal and parietal bones) 2) saggital sutures – btn the 2parietal bones 3)lambdoid sutures- btn occipital and parietal bones

34. Land marks ; Bregma ;meeting point of the sagittal and coronal sutures.in the newborn this forms the anterior fonatanelle which closes st the age of 18months and its diamond shaped. Lambda;meeting of saggital suture and lamdoid sutures .this formsthe posterior fontanelle in the newborn which closes at the 6monthsand its triangular in shape. Parietal emissary foramen;transmits the emissary vein btn the superior saggital sinus and scalp veins. Parietal eminence;center of ossification of the parietal bones.

35. Parietal emissary foramen. Emissary veins traverse cranial apertures anastomosing intracranial venous sinuses and extracranial veins. Relevancy : Spread of infection from extracranial foci to venous sinuses, e.g. mastoid to the venous sinuses or from the paranasal sinuses to the cavernous sinus . Alternative drainage pathways in cases of venous sinus thrombosis.

36. Norma Verticalis Interna Bones ;frontal bone,parietal bones,occipital bone Sutures;-coronal suture,saggital sutures and Lambdoid sutures. Bony landmarks; bregma ,lambda Grooves for: Superior sagittal sinus (extending from the frontal crest). Middle meningeal vessels Granular foveolae from arachnoid granulations

37. Norma Occipitalis The bones;-2parietal bones -squamous part of the occipital bone -mastoid process. Sutures; saggital suture,lambdoid suture,occipitao -mastoid suture and parieto -mastoid suture. Bony landmarks; 1)External occipital protuberance with the inion as the prominent point. 2)Externa occipital crest. 3)lambda.

38. 4) Asterion ;meeting of 3bones( parietalbone,occipital bone,mastoid bone) or 3sutures(lambdoid suture,parieto -mastoid suture and occipito -mastoid suture). The asterion is appoint of postero -lateral fontanelle in the new born which closes at 3months of age. Also the neurosurgical importance of the asterion is that it overlies the sigmoid sinus. 5) 3 nuchal lines(highest nuchal line ,superior nuchal line and inferior nuchal line).

39. 6) mastoid notch /digastric notch –this gives attachement to the posterior belly of the digastric muscle. 7) mastoid foramen –transmits the –emissary veins btn the sigmoid sinus and occipital veins. also- meningeal branch of the occipital artery.

40. Norma Lateralis The bones ; Frontal bone Parietal bones Occipital bones greater wing of the sphenoid bones Squamous part of temporal bone Zygomatic plus zygomatic arch Styloid process Bones o the face;nasal and maxilla. Deep to ramus of mandible is(infratemporal fossa,pterygomaxillary fissure). Mandible and its ramus.

41. The sutures ; Coronal suture squamous suture( btn parietal bone and squamous part of temporal bone) lambdoid sutures Occipito -mastoid sutures Parieto -mastoid sutures Fronto -zygomatic sutures

42. Bony landmarks 1)pterion I s an H shaped feature formed by 4bones;parietal bone,greater wing of sphenoid bone,frontal bone and squamous part of the temporal bone. In the new born skull represents the anterior-lateral fontanelle and ossifies at 3months. Its clinical importance is that it over lies the anterior branch of the middle meningeal artery.therefore fracture of the pterion will cause tear of the MMA causing epidural hemarrhage /hematoma.

43. 2) asterion 3)superior temporal line-which continues as the supra-mastoid crest. 4)inferior temporal lines 5)external auditory meatus 6)supra-meatal triangle(above the external auditory meatus and inferior to the supra-mastoid crest).its surgical importance is that it froms the lateral wall of mastoid antrum. 7)articular tubercle;this prevents the anterior dislocation of the mandible mandibular fossa –for articulation with the head of the mandible. 8)styloid apparatus.(styloid process plus 5 structures attached to it).

44. Norma Basalis Externa Foramina Incisive foramen: Naso -palatine nerve and Spheno -palatine artery Greater and Lesser Palatine foramina Carotid Canal / Foramen Lacerum: Internal carotid artery and carotid sympathetics / deep petrosal nerve Foramen Ovale : Emissary veins between Cavernous sinus and Pterygoid plexus Glossal pharyngeal nerves' lesser petrosal component Maxillary artery’s accessory meningeal branch Mandibular nerve

45. Foramen spinosum: Middle meningeal artery and Nervous spinosous . Stylo -mastoid foramen: Posterior auricular artery’s stylo -mastoid branch Facial nerve Jugular foramen: anterior to posterior; Inferior Petrosal sinus Glossopharyngeal, Vagus , Accessory nerves, meningeal branches of ascending pharyngeal and occipital arteries Sigmoid sinus

46. Anterior condylar canal/ Hypoglossal canal. Posterior condylar canal: Emissary vein between Suboccipital venous plexus and Sigmoid sinus. Foramen magnum: Medulla/Cord + meninges Vertebral and Anterior and Posterior Spinal vessels

47. Cervical vertebrae 7 cervical vertebrae; numbered 1-7 They are all identified by foramina transversaria They are smaller than thoracic or lumbar vertebrae; bcz bear less wt C3-C6 are typical vertebrae bcz share common features C1 C2 & C7 atypical bcz special features for individual identification

48. Surgical surface anatomy & landmarks: Neck extends from pericraniocervical line superiorly to level of clavicle, scapula & thoracic inlet inferiorly Spines of C2 & C7 most prominent and palpable Other cervical spines indistinct bcz C1 has none, others are covered by ligamentum nuchae & postvertebral muscles Transverse process of C1 can be palpated in hollow region posteroinferior to mastoid apex In adult; body of hyoid bone is at level of C4 Upper border of thyroid cartilage lies at level btwn C4 & C5 Inferior border of cricoid cartilage lies at level of C6 i.e. range of C5-T1 C6 is useful landmark for junction btwn ; larynx + trachea & pharynx + oesophagus

49. Features of typical cervical vertebrae:C3-C6

50. Cont … Body: Small Wider from side-side than before-backward Superior surface is concave transversely with lateral margins projecting upward to articulate with lateral margins of inferior surface of vertebra above (which are beveled downwards); forming synovial uncovertebral joints i.e. joints of Luschka Anterior part of inferior surface of body projects downward over intervertebral disc Several vascular foramina on the posterior surface of body transmit basivertebral veins to form anterior internal vertebral venous plexus

51. Vertebral foramen: Triangular Larger than the body Transmits the cervical expansion of spinal cord Intervertebral foramina: Boundaries: superiorly & inferiorly by pedicles, posteriorly by facet joints, anteriorly by uncovertebral joints & intervertebral discs Articular facets: Flat Superior facet are directed backward & upward Inferior facet are directed forward & downward Transverse processes: Small Pierced by foramen transversarium (transmits vertebral artery + vertebral venous plexus + branch from cervicothoracic ganglion i.e. vertebral nerve) Anterior root which ends in anterior tubercle Posterior root which ends in posterior tubercle Tubercles joined by costotransverse bar Each transverse process has costal element (anterior root + anterior tubercle + costotransverse bar + posterior tubercle) and transverse element (posterior root) spine: Small & bifid

52. Features of atypical vertebrae: atlas/C1

53. Ring shaped Has no body; bcz in embryological dev the centrum (body) of C1 is fused with centrum of C2 to form dens of axis ( wc therefore represents body of C1) Has spine Consists; of left & right lateral masses connected by short anterior arch and long curved posterior arch; left & right transverse processes wc project frm lateral masses Anterior arch: has a median anterior tubercle wc receives attachment for anterior longitudinal ligament while upper border of anterior arch receives attachment for atlantooccipital ligament; posterior aspect of anterior arch has oval facet for articulating with dens of axis to from atlantoaxial joint

54. Posterior arch: median posterior tubercle & groove for vertebral artery + venous plexus + 1 st cervical nerve. Lateral mass: Superior articular facet: large, concave, directed upward medially to articulate with condyle of occipital bone = atlantooccipital joint Inferior articular facet; flat circular & directed downward medially backward tp articulate with facet of axis = lateral atlantoaxial joint Small rough tubercle on medial surface of lateral mass is for attachment of transverse ligament of atlas Transverse processes: elongated larger and stronger than those of other cervical vertebrae. Efficient levers for rotation of atlas

55. Axis; C2

56. Features of axis, cont … Formerly called Os Cheloni bcz resemblance to head of Tortoise Called axis bcz atlas rotates like a wheel around the axis as pivot provided by the odontoid process / dens of axis Dens: Strong tooth-like projection Represents body of atlas fused with body of axis Articulates with anterior arch of atlas anteriorly and transverse ligament of atlas posteriorly Provides attachment for; apical ligament at its apex & alar ligaments at its sides

57. Axis; cont … Prominent anterior margin of inferior surface of body projects downward a considerable length Spine: massive (thick & large), very strong, deeply grooved with a bifid tip Small transverse processes; lack anterior tubercles. Foramen transversarium directed upward & laterally Laminae; thick & strong Superior articular facet; Large flat & circular Encroaches onto pedicle ( wc overhangs foramen transversarium) and body Directed upward & laterally to articulate with articulate with facet of atlas=atlantoaxial joint Inferior facet; Posterior to transverse process Directed downward & forward Articulates with C3

58. C7; vertebra prominens

59. Features of C7, cont … Called vertebra prominens bcz its spine forms a prominent palpable projection in lower part of nuchal furrow Spine; thick long & nearly horizontal, ends in a tubercle Transverse processes; comparatively long but lack anterior tubercles Foramen transversarium small and do not transmit vertebral artery but only transmit accessory vertebral vein

60. Clinical correlates: Carotid tubercle of Chassaignac : anterior tubercle of transverse process of C6 is large & the common carotid artery may be compressed against it medial to anterior border of sternocleidomastoid Luschka’s joints; are the commonest site of osteophyte formation Kippel -Feil syndrome; cervical vertebrae fused + congenitally deformed Occipitalization of atlas; ring of atlas is congenitally fused to base of occipital bone. It’s among the commonest abnormalities of cervical vertebrae

61. Cont … Fracture of odontoid process of atlas; Xteristics : fracture of odontoid.p /dens; rupture of transverse ligament ligament of atlas; usually a/w spinal cord compression Causes: blow to the head; fall from a height hangman’s fracture; Causes; execution by hanging; automobile accident; fall from a height Xteristics ; severe extension injury of neck; fracture of pedicles of axis; forward displacement of axis; separation of axis from C3 There’s expansion of vertebral canal and less spinal cord compression compared to fracture of odontoid.p NB: in execution by hanging death occurs by posterior displacement of dens & rupture of transverse ligament of atlas; crushing the lower part of medulla oblongata wc houses vital centers & continuation of spinal cord. 7) Jefferson fracture of the atlas-thru the lateral masses

62. Fracture of the Atlas - Vertical forces e.g. striking the bottom of a pool in a diving accident compressing the lateral masses between the occipital condyles and the axis drive them apart, fracturing one or both of the anterior or posterior arches

63. Jefferson fracture of Atlas - If the force is sufficient, rupture of the transverse ligament that links the lateral masses occurs resulting in Jefferson or burst fracture

64. Fracture of the axis Usually the fracture occurs at the pars interarticularis and is called called a traumatic spondylolysis of C2 caused by hyperextension of the head on the neck. This fracture has been called a hangman’s fracture In more severe injuries, the body of the C2 vertebra is displaced anteriorly with respect to the body of the C3 vertebra. With or without such subluxation of the axis, injury of the spinal cord and/or of the brainstem is likely, sometimes resulting in quadriplegia or death.

65. Surgical approaches to the cervical spine: INDICATIONS OF CERVICAL SPINE SURGERY: Excision of herniated discs & with subsequent fusion/disc replacement Excision of tumours Reduction + stabilization of fractures or dislocations Laminectomy to decompress spinal cord +/- instrumented fusion/laminoplasty

66. COURSE OF VERTEBRAL & OCCIPTAL ARTERIES: Occipital artery; Arises in front of neck from external carotid artery Courses dorsally & rostrally deep to mastoid process Accompanied by occipital nerve; it pierces deep investing cervical fascia btwn attachments of trapezius and sternocleidomastoid Pierces trapezius and supplies occipital belly of occipitofrontalis, skin and pericranium a/w scalp up to level of vertex Vertebral artery; Arises from 1 st part of subclavian artery Courses btwn longus coli & scalenus anterior Described in 4 anatomical segments as follows:

67. 1 st segment (V1): extraosseous segment; runs frm origin (1 st part subclavian) btwn longus coli & scalenus anterior to enter transverse foramen of C6; NB: at C6/C7 level the vertebral artery lies outside foraminal protection & hence liable to injury if more zealous lateral dissections beyond longus coli 2 nd segment (V2): foraminal segment; Runs in foramina transversaria of all cervical vertebrae except C7 Accompanied by large branch of inferior cervical ganglion & venous plexus wc forms vertebral vein Courses anterior to ventral rami of cervical spinal nerves C2-C6

68. Anatomical variations of entry of vertebral artery into foramina transversaria

69. 3 rd segment (V3): extraspinal segment Emerges from foramen transversarium of C1 medial to rectus capitis lateralis Curves posteromedially behind lateral mass of atlas Ventral ramus of C1 lies on its medial side Then lies on groove on posterior arch of C1 (atlas) Enters ventral canal by piercing lateral angle of atlantooccipital membrane (where calfication forms a foramen; arcuate foramen; ponticulus posticus where V3 passes and shd b identified to avoid its injury) 4 th segment (V4): intradural segment; Runs from foramen magnum to pontomedullay junction Here the left & right vertebral arteries join to form basilar artery

70. Broad classification of anomalies of vertebral artery: Interforaminal anomalies; midline migration of v. artery Extraforaminal anomalies; variable level of entry of v. artery into foramen tranversarium Interarterial anomalies; fenestrated; hypoplastic; v. artery may course in groove of posterior arch C1 without passing via transverse foramen of C1

71. Surgical approaches & considerations: Anterior approach to occipitocervical (OC) region: Via submandibular incision Exposes retropharyngeal space and ventral aspect of atlas + axis Ideal for decompression & fusion of OC junction Posterior approach to OC: Via midline neck incision Through interneural plane which is relatively avascular Take care when placing C1 lateral mass screw fixation bcz proximity of V3 as it exits C2 foramen transversarium

72. Anterior approach to cervical spine: Exposes anterior vertebral bodies of C3-T1 Incisions: Transverse skin incision at appropriate level of vertebral pathology Longitudinal skin incision over midpoint of sternocleidomastoid Incision 3-4 fingerbreadths above clavicle exposes C3-C5 Incision 2-3 fingerbreadths above clavicle exposes C5-C7 Avoid dissections lateral to sternocleidomastoid so as to avoid injury to accessory nerve Other structures at risk of injury include: trachea, oesophagus, recurrent laryngeal nerve, sympathetic chain (hence Horner’s syndrome/ptosis sympathetica /Bernard-Horner syndrome= ptosis +miosis + anhidrosis + enopthalmos ) NB: intra-op fluoroscopy is used to confirm c-vertebral level during surgery so as to minimize iatrogenic injury Posterior approach to cervical spine: Incision midline & dissection relatively safe ( bcz posterior muscle fibres course longitudinally & muscles are supplied by segmental nerves) However incision perpendicular to tension line of skin & hence forms a thicker scar

73. Thoracic vertebrae General features Presence of atleast 1 articular fact on the body for rib articulation The bodies enlarge from up- downwards

74. Typical vertebrae(T2-T10) Body is heart shaped and lies anteriorly Vertebral foramen is circular The spine is long and projects downwards The stout transverse process project backwards The body has 2 articular facets(upper-corresponding rib, lower- rib below) Thin intervertebral discs

75. Atypical thoracic vertebrae(t1 and T11-12) Single round articulating facet for head of corresponding rib T11-12, costal facet encroaches on pedicle T11-12, have small transverse processes which don’t articulate with corresponding rib Lower spines become shorter & less oblique and look rectangular The inf articular surface of T12 faces laterally and anteriorly

76. Lumbar Vertebrae The bodies of lumbar vertebrae increase in breadth from above down Posteriorly there is a progressive widening between the articular processes The body is kidney shaped and pedicles are attached to its upper half as well as perforated by a pair of basivertebral veins posteriorly(similar to thoracic verbrae ) The transverse processes are variable in length, but the fourth is usually the longest

77. The pedicles are stout and form the upper and lower margins of the intervertebral foramina The laminae do not show such a downward slope as in the thoracic vertebrae. The quadrangular spinous process is roughly horizontal. The upper border is straight but the lower border is concave . The articular processes of the upper pair rise up and carry articular facets that face medially. The articular surfaces are concave from front to back. The lower pair of articular processes project down , face laterally and are convex from front to back.

78. The transverse processes are fused ribs The true transverse element consists of two small elevations with a groove between them occupied by the medial branch of the posterior ramus of the overlying lumbar nerve . The inferior articular processes of the fifth lumbar vertebra face well forwards* Lumbarization and sacralization *

79. Sacrum Five progressively smaller sacral vertebrae and their costal elements fuse to make this bone It’s triangular in outline and curved with a concavity towards the pelvis its lateral aspect it has an auricular surface for articulation with the ilium to make the upper posterior wall of the pelvis The upper surface of the first sacral vertebra forms the base of the sacrum The body of S1 vertebra is large, and wider transversely; its anterior projecting edge is the sacral promontory

80. Lateral to the body is the wing-like ala of the sacrum on each side, consisting of fused costal elements and transverse processes* Pelvic surface S urface is smooth The midline five diminishing bodies are fused, with four ridges persisting to mark the lines of ossification On each side are the four anterior sacral foramina The rounded bar of bone above the first sacral foramen continues the arcuate line of the ilium to form the posterior part of the pelvic brim

81. The mass of bone lateral to the foramina, the lateral mass , is formed by fusion of the costal elements* Peritoneum is draped over the front of the upper two bodies and below that level the retroperitoneal rectum lies surrounded by the mesorectum From the front of the lower sacrum the rectosacral fascia passes downwards and forwards to fuse with the mesorectum 3–5 cm above the anorectal junction*

82. Dorsal surface This convex surface is irregular and rough In the midline it is closed by fusion of adjacent laminae The gap above the first sacral laminae is closed by the ligamenta flava attached to the laminae of L5 vertebra The sacral hiatus below indicates failure of fusion of the laminae of S5 and often of S4 vertebrae Adjacent spinous processes are fused with each other to produce a midline ridge,the median sacral crest

83. The superior articular process on S1 vertebra carries a backward facing facet for the synovial joint with L5 vertebra M edial to the posterior foramina is a line of irregular tubercles that represent fusion of adjacent articular processes of the sacral vertebrae,the intermediate sacral crest it is projected below, alongside the sacral hiatus, to end in the rounded sacral cornu Lateral to the superior articular process is a prominent boss of bone which is the transverse process of S1 vertebra and b elow this the transverse processes are fused with each other formingthe lateral sacral crest

84. Sacral canal This is triangular in cross-section and curves with the sacrum The sacral canal contains the meninges which extend down to S2 vertebra

85. Clinical significance Sex differentiation between male and female The body is wider than the ala in the male, equal to or narrower than the ala in the female In the male the anterior surface is gently and uniformly concave while female it is flat above and turns forward more prominently below. The auricular surface occupies two and a half vertebrae in the male, but is smaller in the female and may be restricted to two vertebrae

86. Coccyx This is contracted into four pieces fused together into a small triangular bone joined by its base to the apex of the sacrum at the sacrococcygeal joint At each side a lateral sacrococcygeal ligament joins the transverse process of the first piece of the coccyx to the inferolateral angle of the sacrum This completes the foramen for S5 nerve anteriorly and posteriorly the foramen is closed by the sacral and coccygeal cornua connected by the intercornual ligament The upper surface of the coccyx is in the pelvic floor , the lower surface is in the buttock, beneath the skin of the natal cleft

87. Clinical correlates Abnormal curvatures

88. Cervical rib- Development of the costal element of C7 Supernumerary rib - a fibrous connection extending from the tip of C7 to the first thoracic rib may elevate and place pressure on structures that emerge from the superior thoracic aperture, notably the subclavian artery or inferior trunk of the brachial plexus, and may cause thoracic outlet syndrome.

89. Joints of the Vertebral Column These include: Joints of the vertebral bodies . Joints of the vertebral arches. Craniovertebral ( atlanto -axial and atlanto -occipital) joints Costovertebral joints. Sacro -iliac joints

90. JOINTS OF VERTEBRAL BODIES The joints of the vertebral bodies are symphyses (secondary cartilaginous joints) designed for weight-bearing and strength The articulating surfaces of adjacent vertebrae are connected by intervertebral discs and ligaments Each IV disc consists of an anulus fibrosus , an outer fibrous part, composed of concentric lamellae of fibrocartilage, and a gelatinous central mass, the nucleus pulposus . There is no IV disc between C1 and C2 vertebrae; the most inferior functional disc is between L5 and S1 vertebrae

91. The anterior longitudinal ligament is a strong, broad fibrous band that covers and connects the anterolateral aspects of the vertebral bodies and IV discs The ligament extends longitudinally from the pelvic surface of the sacrum to the anterior tubercle of vertebra C1 and the occipital bone anterior to the foramen magnum are the superiormost parts, the anterior atlanto -axial and atlanto -occipital ligaments . This ligament prevents hyperextension of the vertebral column, maintaining stability of the joints between the vertebral bodies

92. The posterior longitudinal ligament runs within the vertebral canal along the posterior aspect of the vertebral bodies . This ligament weakly resists hyperflexion of the vertebral column and helps prevent or redirect posterior herniation of the nucleus pulposus

93. JOINTS OF VERTEBRAL ARCHES Also called the zygapophysial joints (facet joints). These articulations are plane synovial joints between the superior and inferior articular processes of adjacent vertebrae Each joint is surrounded by a thin joint capsule and it is attached to the margins of the articular surfaces of the articular processes of adjacent vertebrae Accessory ligaments unite the laminae, transverse processes, and spinous processes and help stabilize the joints.

94. CRANIOVERTEBRAL JOINTS There are two sets of craniovertebral joints, the atlanto -occipital joints, formed between the atlas (C1 vertebra), and the occipital bone of the cranium, and the atlanto -axial joints, formed between the atlas and axis (C2 vertebra ) The craniovertebral joints are synovial joints that have no IV discs

95. Atlanto -occipital Joints. The articulations are between the superior articular surfaces of the lateral masses of the atlas and the occipital condyles These joints permit nodding of the head and also permit sideways tilting of the head The main movement is flexion, with a little lateral flexion and rotation. They are synovial joints of the condyloid type and have thin, loose joint capsules

96. The cranium and C1 are also connected by anterior and posterior atlanto -occipital membranes, which extend from the anterior and posterior arches of C1 to the anterior and posterior margins of the foramen magnum The anterior membranes are composed of broad, densely woven fibers and posterior membranes are broad but relatively weak The atlanto -occipital membranes help prevent excessive movement of the atlanto -occipital joints.

97. Atlanto -axial Joints There are three atlanto -axial articulations i.e. T wo (right and left) lateral atlanto -axial joints (between the inferior facets of the lateral masses of C1 and the superior facets of C2 ) O ne median atlanto -axial joint (between the dens of C2 and the anterior arch of the atlas ). The lateral atlanto -axial joints are gliding-type synovial joints whereas the median atlanto -axial joint is a pivot joint . Movement at all three atlanto -axial joints permits the head to be turned from side to side

98. Vasculature of the column Vertebrae are supplied by periosteal and equatorial branches of the major cervical and segmental arteries and their spinal branches Parent arteries of the above arise from; Vertebral and ascending cervical arteries in the neck Posterior intercostal arteries in the thoracic region Subcostal and lumbar arteries in the abdomen Iliolumbar and lateral and medial sacral arteries in the pelvis

99. Periosteal and equatorial branches arise from these arteries as they cross the anterolateral surfaces of the vertebrae . Spinal branches enter the IV foramina and divide Smaller anterior and posterior vertebral canal branches pass to the vertebral body and vertebral arch, respectively. They give rise to ascending and descending branches that anastomose with the spinal canal branches of adjacent levels Anterior vertebral canal branches send nutrient arteries anteriorly into the vertebral bodies that supply most of the red marrow of the central vertebral body

100. The larger branches of the spinal branches continue as terminal radicular or segmental medullary arteries distributed to the posterior and anterior roots of the spinal nerves and their coverings and to the spinal cord, respectively.

101. Spinal veins form venous plexuses along the vertebral column both inside and outside the vertebral canal These plexuses are the internal vertebral venous plexuses (epidural venous plexuses) and external vertebral venous plexuses, respectively The large, tortuous basivertebral veins form within the vertebral bodies and emerge from foramina on the surfaces of the vertebral bodies

102. They then drain into the anterior external and especially the anterior internal vertebral venous plexuses, which may form large longitudinal sinuses . The intervertebral veins receive veins from the spinal cord and vertebral venous plexuses as they accompany the spinal nerves through the IV foramina to drain into the vertebral veins of the neck and segmental (intercostal, lumbar, and sacral) veins of the trunk

103. Reference: Gray’s surgical anatomy Vishram Singh Textbook of anatomy of head & neck