Dr. Akram M. Asbeutah, PhD Department of Radiologic Sciences Faculty of Allied Health Sciences

1. Dr. Akram M. Asbeutah, PhD Department of Radiologic Sciences Faculty of Allied Health Sciences Kuwait University Development of the Skeletal system

2. Developmental Anatomy-Introduction 5th Week= limb bud appears as mesoderm covered with ectoderm 6th Week= constriction produces hand or foot plate and skeleton now totally cartilaginous 7th Week= endochondral ossification begins 8th Week= upper & lower limbs appropriately named

3. Developmental Anatomy-Introduction • As the notochord and neural tube form, the intraembryonic mesoderm lateral to these structures thickens to form two longitudinal columns of paraxial mesoderm • At the end of 3rd week, these dorsolateral columns becomes segmented (somites) • Each somite differentiates into two parts • The ventromedial part (Sclerotome)-form vertebrae & ribs • The dorsolateral part (dermomyotome)- cells forms myoblasts and dermis

4. Intramembranous Ossification • Both types of bone formation begin with mesenchymal cells • Mesenchymal cells become osteoblasts which form bone OR • Mesenchymal cells transform into chondroblasts which form cartilage

5. Endochondral Ossification • Mesenchymal cells transform into chondroblasts which form cartilage • Three types of cartilage are distinguished according to the type of the matrix that is formed: • Hyaline cartilage • Fibrocarilage • Elastic cartilage

6. Development of Joints • Joints develop from interzonal mesenchyme between the primordia of bones • They are classified as fibrous, cartlagenous, and synovial joints • In a fibrous joint, the intervening mesenchyme differentiates into dense fibrous connective tissue • In a cartilagenous joint, the mesenchyme between the bones differentiates into cartilage • In a synovial joint, a synovial cavity is formed within the intervening mesenchyme by breakdown of the cells. Mesenchyme also give rise to the synovial membrane, capsule, and ligaments of the joint

7. Development of The Axial Skeleton • Cranium, vertebral column, ribs, & sternum • During the 4th week, cells in the sclerotomes surround the neural tube (primordia of spinal cord) and the notochord (primordia of the vertebrae)

8. Development of the Vertebral Column & Ribs • The vertebral column & ribs develop from mesenchymal cells derived from the sclerotomes of the somites • Each vertebra is formed by fusion of a condensation of the caudal half of one pair of sclerotomes with the cranial half of the subjacent pair of the sclerotomes • Some densely packed cells move cranially, where they form the intervertebral disc • The nototochord degenerates and disappears where it is surrounded by the developing vertebral bodies. Between the vertebrae, the notohord expands to form the nucleus pulposus and surrounded latter by anulus fibrosis. Remenants of the notochord cause chordoma (slow-growing malignant tumours (cranial or Lumboscaral regions) • The neural arch is formed by the mesenchyme surrounding the neural tube • Variation in the number of the vertebrae (extra or absent)

9. Development of the Sternum • A pair of vertical mesenchymal bands 9sternal bars), develops ventromedially in the body wall • Chondrofication occurs in these bars as they move medially • They fuse craniocaudally in the median plane tp form cartilagenous models of the manubrium, body, and xiphoid process • Centers of ossification appear craniocaudally in the sternum before birth, except that for xiphoid process, which appears during childhood • A concave depression of the lower sternum (pes excavatum) is the most common thoracic wall defect that occur because of overgrowth of the costal cartlages, which displaces the lower sternum posteriorly

10. Development of the Cranium • The cranium (skull) develops from the mesenchyme around the developing brain • The developing cranium consists of a neurocranium and a viscerocranium, each of which has membranous and cartilagenous components • The neurocranium forms the clavaria by membranous ossification and base of the skull by endochondral ossification • The viscerocranium forms the skeleton of the face (membranous) and some craniofacial (endochondral)

11. Axial Skeleton Congenital Anomalies • Klippel-Feil Syndrome • Spina bifida • Accessory ribs • Fused ribs • Hemivertebra • Rachischisis • Anomalies of the sternum • Cranial anomalies (acrania, craniosynostosis, microcephaly) • Cranioveretebral junction anomalies

12. Klippel-Feil Syndrome • The main features of this syndrome are shortness of the neck, low hairline, and restricted neck movements • In most cases the number of vertebral bodies is fewer than normal • The number of cervical nerve roots may be normal but they are samll, as are the intervertebral formina • Association with other congenital anomalies is common

13. Spina Bifida • Failure of the halves of the neural vertebral arch to fuse • Incidence 0.04%-0.15%. More in girls than boys • 80% are open and covered by a thin membrane • Spina bifida occulta (closed) is covered by skin or thick membrane • Spina bifida cystica involving the spinal cord and meninges (meningeocele or myelomeningeocele)and neurologic symptoms are present

14. Accessory Ribs, Fused Ribs, & Hemivertebra • A lumbar rib and causes no problems • A cervical rib occurs in 0.5% to 1% of individuals and can be unilateral or bilateral and cause neurovascular symptoms • Fused ribs usually associated with hemivertebra • Hemivertebra results from failure of one of the chondrification centers to appear

15. Rachischsis • The term rachischisis (cleft vertebral column)refers to the vertebral abnormalities in a complex group of anomalies (axial dysraphic disorders) • In thses infants, the neural folds fail to fuse, either because of faulty induction by the underlying notochord or from the action of tertogenic agents on the neuroepithelial cells in the neural folds

16. Cranial Anomalies [Acrania, Craniosynostosis, & Microcephaly] • These abnormalities range from major defects that are incompatible with life to those that are minor and insignificant • Acrania, the clavaria and extensive defects of the vertebral column are often present. Acrania associated with anencephaly occurs in 1 in 1000 births and is incompatible with life • Craniosynostosis results from prenatal closure of the cranial sutures and has many types: • Scaphocephaly (Sagitall suture) • Brachycephaly (coronal suture) • Plagiocephaly (one side of coronal suture) • Trigonocephaly (metopic suture) • Microcephaly results from abnormal development of the central nervous system and not premature closure of sutures

17. Dr. Akram M. Asbeutah, PhD Department of Radiologic Sciences Faculty of Allied Health Sciences Kuwait University Development of the Limbs

18. Early Stages of Limbs Development (Appendicular Skeleton) • The appendicular skeleton develops from endochondral ossification of the cartlagenous bone models, which from from mesenchyme in the developing limbs

19. Early Stages of Limbs Development • Limb buds appear toward the end of the 4th week as slight elevations of the ventrolateral body wall • The upper limb buds develop 2 days before the lower limb buds • Intially, the developing limbs are directed caudally; later they project ventrally, and finally, they rotate on their longitudinal axes. The upper limb and lower limbs roate in opposite directions and to a different degrees • The tissues of the limb buds are derived from two main sources: • Mesoderm • ectoderm

20. Early Stages of Limbs Development • The apical ectodermal ridge (AER) exerts an inductive influence on the limb mesenchyme, promoting growth and development of the limbs • The limb buds elongate by proliferation of the mesenchyme within them • Apoptosis (programmed cell death is an important mechanism in limb development (e.g. in the formation of the notches between the digital rays)

21. Early Stages of Limbs Development

22. Final Stages of Limbs Development • The limb elongate, mesenchymal models of the bones are formed by celluar aggregation • Chondroification centers appear in the 5th week • By the end of the 6th week, the entire limb skeleton is cartilagenous • Osteogenesis of long bones begins in the 7th week from primary ossification centers in the middle of the cartilagneous models of the long bones • Ossification centers are present in all long bones by the 12th week but for the wrist bones only begins during the first year after birth

23. Final Stages of Limbs Development • Limb muscles are derived from mesenchyme (myogenic precursor cells) originating in the somites • The muscle forming cells (myoblasts) form dorsal and ventral muscle masses

24. Cutaneous Innervation of Limbs • Nerves grow into the limb buds after the muscle masses have formed

25. Blood Supply to the Limbs • Most blood vessels of the limb buds arise as buds from the intersegmental arteries and drain into the cardinal veins

26. Anomalies of the Limbs • The majority of limb anomalies are caused by genetic factors and many limb defects result from an interaction of both genetic and environmental factors (multifactorial inheritance) • Appendicular anomalies Generalized Skeletal Malformations (achondroplasia, thanatophoric dysplasia), Hyperpituitarism (gigantism or acromegaly), Hypothyroidism (cretinism) • Amelia • Cleft hand & foot • Congenital absence of the radius • Brachchydactyly • Polydactyly • Syndactyly • Congenital clubfoot • Congenital dislocation of the hip

27. Limb Anomalies-Amelia • Amelia (absence of limbs or part of a limb (meromelia) due to exposure to a teratogen -thalidomide • A-Amelia • B- Absence fibula and short right leg with hypoplastic and bowed femur and tibia • C- Short leg with absence lower leg bones • D- Absence middle digits • E- absence of mid toes 2-4

28. Limb Anomalies- Polydactyly & Syndactyly • Polydactyly: Supernumerary digits • Syndactyly: Failure of the webs to degenerate between two or more digits

29. Limb Anomalies- Clubfoot • Any deformity of the foot involving the talus is called talibes or clubfoot • Talibes equinovarus is the most common • It occurs 1 in 1000 birth • The sole of the foot turned medially and the foot is inverted • It is bilaterally in 50% of cases and it occurs twice in males • Unknown cause but the fetus foot position has an effect

30. Dr. Akram M. Asbeutah, PhD Department of Radiologic Sciences Faculty of Allied Health Sciences Kuwait University Development of the Muscular system

31. Development of the Skeletal Muscle • Trunk muscles: myotomal mesoderm of the somites • Limb muscles: mesedorm in the limb buds • Tongue muscles and many muscles of the face, jaws, neck, & shoulders develop from mesedorm in the pharyngeal arches

32. Development of the Skeletal Muscle • Myoblasts • Myotubes (many myoblasts), elongated, multinucleated cylindrical structures • Myofilaments and myofibrilis develop • Most striated skeletal muscle fibers develop before birth, and almost all the remaining ones are formed by the end of the first year

33. Myotomes • Each myotome divides into: • A small dorsal epaxial division • A large ventral hypaxial division • Each developing spinal nerve divides and sends a branch to each division • Dorsal primary ramus (epaxial) • Ventral primary ramus (hyaxial)

34. Derivatives of Epaxial Divisions of Myotomes • Extensors muscles of the • Neck • Vertebral column up to the lumbar region • The sacral and coccygeal degenerate and form the sacrococcygeal ligaments

35. Derivatives of Hypaxial Divisions of Myotomes • Cervical myotomes form the scalene, prevertebral, geniohyoid, & infrahyoid muscles • The thoracic myotomes form the lateral & ventral flexor muscles of the vertebral column • The lumbar myotomes form the quadratuslumborum muscle • The sacrococcygealmyotomes form the muscles of the pelvic diaphragm and the striated muscles of the anus and the sex organs

36. Pharyngeal Arch Muscles

37. OccularMuscles& Tongue Muscles • Occular muscles: meseoderm close to prochordal plate • Tongue muscles: four pairs of occipital myotomes

38. Limb Muscles • They develops from the mesoderm surrounding the developing bones • This is derived from the somatic layer from lateral mesoderm

39. Development of Smooth Muscle • Splanchnic mesoderm surrounding the endoderm of the primitive gut • Somatic mesoderm gives the smooth muscles in the wall of the blood and lymphatic vessels • Muscles f the iris, myoepithelial cells of the mammary and sweat glands are derived from mesenchymal cells rom ectoderm

40. Development of Cardiac Muscle • Cardiac muscles develops from the splanchnic mesenchyme surrounding the endocardial heart tubes • Cardiac myoblasts differentiate from the myoepicardial mantle and form the myocardium • Atypical cardiac muscles cells (Purkinje cells) develop and later form the conducting system of the heart

41. Anomalies of Muscles • Poland Syndrome • Arthrogryposis multiplex congenita • Congenital absence of the diaphragm • Variations in muscles • Congenital Torticollis