Spine development

Embryonic Stages and Germ Layers

  • 17th Day of Gestation:
    • The embryo enters the triploblastic stage, consisting of three germ layers:
      • Endoderm
      • Ectoderm
      • Mesoderm
    • Through a process called gastrulation, these layers position themselves and begin interacting, setting the anteroposterior axis of the embryo and initiating neural development from the ectoderm.

Formation of the Notochord and Neural Plate (Third Week)

  • Notochord Formation:
    • Appears during the third week.
    • Acts as a foundation for the spinal column.
    • Later transforms into the nucleus pulposus of intervertebral discs.
  • Neural Plate and Neural Tube Formation:
    • The notochord induces the formation of the neural plate.
    • By the fourth week, the neural plate folds into the neural tube through a process called neurulation.

Somites and Spinal Development

  • Somite Formation:
    • Pairs of somites emerge from the mesoderm.
    • Sclerotome: Becomes the vertebral body and annulus fibrosus.
    • Myotome: Develops into muscles.
  • Sclerotome Transformation (Fourth Week):
    • Surrounds the notochord to form vertebral bodies and annulus fibrosus.
    • Grows around the neural tube to form vertebral arches.
    • Inter-segmentation occurs:

      • Front half of one sclerotome fuses with the back half of the next to form a single vertebra.

      • This explains the segmental blood supply pattern.

Ossification Process of Vertebrae

  • 7-8 Weeks Gestation:
    • Ossification begins, with the exception of C1 (atlas), C2 (axis), and the sacrum.
  • Three Stages of Ossification:
    • Starts in the lower thoracic and upper lumbar regions.
    • Progresses cranially and caudally.
    • Cartilage centers form and unite to create:
      • Vertebral body
      • Neural arch
      • Apophyses on the transverse and spinous processes.

Key Developmental Stages

Stage Developmental Activity
Week 3 Formation of the notochord and initiation of the neural plate.
Week 4 Neural plate folds into the neural tube, somites form.
Week 7-8 Ossification begins, centers form in vertebral regions.

Growth Zones in Vertebrae

  • Three growth zones contribute to the structure of vertebrae:
    • Center of the vertebral body
    • Neural arch
    • Transverse and spinous processes
  • Each vertebra results from approximately 100 growth plates.

Neurocentral Synchondrosis

  • Definition:
    • A growth plate located at the junction between the vertebral body and the pedicle.
  • Role in Growth:
    • Critical for the development of the vertebral body and posterior arch.
  • Developmental Timeline:
    • Fusion by age 9 in humans, allowing for normal spinal development.
    • Intervention Impact:
      • Screw fixation crossing this plate before fusion can lead to scoliosis in growing animals, but not after the age of 10.

Key Milestones in Spinal Development

Developmental Stage Key Event
Week 17 Triploblastic stage and gastrulation begin.
Week 3 Notochord formation, neural plate development.
Week 4 Neural tube formation and somite development.
Week 7-8 Ossification of vertebrae begins.
Age 9 Neurocentral synchondrosis fuses.
Back to top