The Pelvic Girdle Fusion of pelvic and sacral elements

Os coxa

At birth, all three bones of the os coxa are present: ilium, ischium, and pubis. These three bones do not all fuse together at the same time, but in a specific order at different times. Additionally, there are numerous small and ‘ossific islands’ that appear and fuse during growth and development, but only the bigger and main epiphyses will be discussed here.

Ischium and pubis

The first bones to fuse are the ischium and pubis along the ischiopubic ramus (Caffey and Madell 1956; Cardoso et al. 2013). This normally occurs in individuals around ages 5 to 8 years although earlier has been reported (Scheuer and Black 2004).

Around 14 to 18 years of age, the acetabulum begins and completes fusion, ossifying the ilium, ischium, and pubis together.

Ilium

Specifically for the ilium, around 10 to 13 years of age, the ossification center for the anterior inferior iliac spine appears and fuses between 14 and 18 (Maclean 2014).

The iliac crest begins ossification around 12 to 14 years in females and 14 to 17 in males. This epiphysis completes fusion between 17 to 22 years old (Scheuer and Black 2004; Buikstra and Ubelaker 1994).

Although there are many more centers of small and flaky epiphyses that begin ossification and fuse throughout this whole process, there is not enough space and not enough need to warrant a more in-depth discussion here.

Sacrum

Although technically comprised of vertebrae, the sacrum is placed in the pelvis section of this project for its participation in the pelvic inlet and the morphology of the pelvic girdle overall.

The average human has 5 sacral elements, but they do not all fuse in the same way or with the same number of elements. S1-S3 are each comprised of 5 different ossification centers: one centrum, two lateral elements, and two half neural arches. S4 and S5 each have only three: one centrum and two half neural arches (Fawcett 1907).

Over time, all of these elements will eventually fuse to become one single bone, but their timing and sequence of fusion can aid in age estimation.

At birth, the average human has a sacrum comprised of 21 individual parts, each of those listed above. Between 2 and 6 years, each of the parts within a sacral vertebra will start to fuse together, such that by the time an individual is 7 years old, there will only be 5 parts left, one for each sacral vertebra (Cardoso et al. 2014).

In the early teen years, the number of sacral segments is variable and changes such that many of the areas of sacral segments begin to fuse together with no true and specific pattern (at least that research has shown thus far).

By the end of puberty, there is only one sacral element, though not all elements may have completely fused together yet. Due to the many elements in the sacrum, it does not fully cease fusing until around 25 years old (Cardoso et al. 2014).