NORMAL OSSIFICATION CENTERS OF THE SPINE

• 3 primary ossification centers:
• Body (centrum). Initially in the lower thoracic and upper lumbar region followed by progressive cranial and caudal ossification.
• Left and right posterior neural arches ossify in a cephalo-caudal direction. Ossification begins at the base of the transverse process and spreads to involve the laminae and pedicles.
• Lower thoracic, upper lumbar = 8-12 weeks gestational age.
  Lower cervical = 12-14 weeks gestational age.
  Mid cervical = 14-16 weeks gestational age.
  Upper cervical = 16-120 weeks gestational age.
• Ossification of the laminae.
• Cervical region by 18-19 menstrual weeks
• Thoracic region by 20-22 menstrual weeks
• Lumbar region by 22-24 menstrual weeks
• Sacral spine by 22-25 menstrual weeks.

Although ossification is only complete by 25 weeks there is usually enough ossification present by 18-20 weeks to assess for a spinal defect.