Function of Spine
Flexibility
Shock absorption
support for extremities and cranium
structural support for respiratory function
Stages of Fetal Development
Pre-embryonic Period: first 3 weeks after fertilization
Embryonic Period: lasts from week 3 to week 8, development of organs
Fetal period: week 8 until term, maturation and growth of all structures
Early Development
Skeletal, muscular, and neural development is related to the notochord
Cell proliferation occurs at 3 weeks–formation of ectoderm, mesoderm, and endoderm
Proliferation of Mesoderm- formation of 29 pairs of somites, formed in 4th and 5th weeks
–Somites = pair of block like segments that give rise to mm and vertebrae on each side of notochord
Differentiation of Somites = 4 occipital, 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 8-10 coccygeal somites
Proliferation of Somites- development of 3 areas
- Dorsal: cells become dermatomes = skin
- Medially: deep migration = skeletal mm
- Ventral and Medial: cells migrate to neural tube = sclerotome
Sclerotome- proliferate and differentiate giving rise to vertebral structures including rib buds
– Chrondification begins at CT level, extending cranially to caudally, allows for formation of solid cartilage model of vertebra with no line of demarcation btwen body, neural arch or rib rudiments
Ossification
Ossification- primary and secondary centers
- begins during late fetal period and continues after birth
1. Primary: extend to spinous, transverse, and articular processess
2. Secondary: develop at the upper and lower portions of vertebral body, tip of spinous process, and each transverse process - continues through adolesence, includes ribs
Ossification of axis, atlas, and sacrum:
Atlas: 2 primary and 1 secondary
Axis: 5 primary and 2 secondary, begins near the end of gestation with fusion of odontoid centers, completed in second decade of life
Sacrum: fusion begins in adolescence and completed in 3rd decade of life
Spinal Growth
Occurs throughout adolescence
Does not proceed in a uniform linear pattern, however it is linear between 3 y/o to puberty
2 periods of rapid spinal growth:
- Birth-age 3
- Adolescent growth spurt
Spinal pubertal growth spurt occurs at different chronologic and tanner ages.
Females: Tanner 2, 8-14 y/o, max growth at 12 y/o, growth spurt lasts 2.5-3 years
Males: Tanner 3, 11-16 years, max growth at 14