Children are not born with an adult skeleton. At birth, much of the skeleton is cartilaginous, but after birth, a process of ossification begins. Bone ossification, or osteogenesis, is the process of bone formation. This process starts during embryonic development in the primary ossification centres. After birth, secondary ossification centres develop in each end of long bones which promote both length and shape to bones. The primary and secondary ossification centres are separated by the epiphyseal growth plate.
The growth plate (the physis) is split into several layers and enables the process of ossification and elongation of the long bones. Once maximal length is achieved the growth plate fuses. Other secondary ossification centres create shape not length, providing attachments for ligaments and tendons (apophyses),
The timing of ossification is different from bone to bone but occurs in a predictable sequence of development and progression until around the age of 25-30. There is conflict across the research, and it is thought that these figures may vary across population groups.
In children of the same chronological age, bone maturation is approximately 2 years earlier in girls than in boys. In addition, children all mature at different rates, with some children maturing as much as 3 years earlier or later than their peers.
Several factors affect maturation including:
- Gender
- Hormones
- Ethnicity
- Pathology
- Stress
- Genetics
Certain conditions that affect adolescents can only occur when the physis is open. For example, Sever’s is the primary cause of heel pain in sporty children aged between 8-14 when the calcaneal physis is open. Once the physis fuses post puberty, Sever’s is no longer a consideration and other differential diagnoses must be sought.
Knowledge and understanding of paediatric anatomy, the timing and pattern of secondary ossification centre appearance, and an assessment of maturation is therefore important to be able to assess skeletal development, and to be able to make an accurate clinical diagnosis.
Click here to download the ossification sequence of different regions of the body.
