Musculoskeletal System - Bone Development Timeline

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.