Musculoskeletal System - Bone Development Timeline: Difference between revisions
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At birth mandible still has separate right and left halves. | At birth mandible still has separate right and left halves. | ||
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Year 1 - Fusion of right and left halves of mandible at the symphysis. | Year 1 - Fusion of right and left halves of mandible at the symphysis. | ||
Revision as of 17:25, 2 February 2011
Introduction
The adult human skeleton has about 206 different bones which are formed from fusion of significantly more bones in the postnatal developing neonate and child (about 275). Ossification in general continues postnatally, through puberty until mid 20s.
The two major parts of the human skeleton are the axial (80 bones in skull, vertebra, ribs, sternum) and appendicular (126 bones in limbs, shoulders, pelvis) skeletons.
These notes summarise the timecourse of development of some of these bones in humans.
Two main forms of ossification occur in different bones, intramembranous (eg skull) and endochondral (eg vertebra) ossification.
Endochondral ossification within the limb begins at Carnegie stage 18 and also occurs throughout embryo skeleton. This process is the replacement of a cartilage "template" with bone (week 5-12) that continues through postnatal development, with a second surge of growth at puberty.
Ossification Stages
The process of ossification as determined postnatally clinically has been divided into a series of stages.[1]
- Stage 1 - non-ossified epiphysis
- Stage 2 - discernible ossification centre
- Stage 3 - partial fusion
- Stage 4 - total fusion
- Stage 5 - an additional stage recently added is the disappearance of the epiphyseal scar after total fusion.
Long Bones
Humerus
Appearance and fusion of bone secondary ossification centres, proximal is closer to body and distal is further away from the body.
Appearance
- Proximal epiphysis gestation week 36 - 4 years
- Distal epiphysis 6 months - 10 years
Fusion
- Proximal epiphysis 12 - 20 years
- Distal epiphysis 11 - 19 years
Femur
Appearance
- Proximal epiphysis 1 - 12 years
- Distal epiphysis Gestation week 36 - 40
Fusion
- Proximal epiphysis 11 - 19 years
- Distal epiphysis 14 - 19 years
Data from reference Table 1 [2]
Mandible Development
Prenatal
Week 6 - Intramembranous ossification center develops lateral to Meckel's cartilage.
Week 7 - Coronoid process begins differentiating.
Week 8 - Coronoid process fuses with main mandibular mass.
Week 10 (approx) - Both condylar and coronoid processes are recognizable and anterior portion of Meckel's cartilage begins to ossify.
Weeks 12-14 - Secondary cartilages for the condyle, coronoid, and symphysis appear.
Weeks 14-16 - Deciduous tooth germs start to form.
Birth
At birth mandible still has separate right and left halves.
Postnatal
Year 1 - Fusion of right and left halves of mandible at the symphysis.
Infancy and childhood - Increase in both size and shape of the mandible; eruption and replacement of teeth.
Year 12-14 - All permanent teeth emerged except third molars.
Data from: table 4 - Species comparison of postnatal bone growth and development. Birth Defects Research (Part B) 68:86-110, 2003.
