Reconstructing articular cartilage in the Australopithecus afarensis hip joint and the need for modelling six degrees of freedom
The first paper of my Leverhulme Trust funded project has just been published in Integrative Organismal Biology – Read the paper here!
A detailed post about the paper, methods and results can be found on the Projects Update page of this website, but the abbreviated version…
Example of rotational movement of the hip in the AL 288-1 specimen
To sum up (TLDR): We tested the articulation and possible osteological ROM of the AL 288-1 hip joint by modelling a static single axis translation to investigate increasing joint spacing, which was considered a proxy for measuring maximum cartilage thickness. We expanded upon this by including all six DOFs, thereby reflecting true joint movement. Whilst the resultant ROM maps were quite similar, there was a greater spectrum of viability in the six DOF simulation than the other simulations, in which the femur was capable of osteologically moving into a greater range of poses. With this spectrum of poses, AL 288-1 was capable of a repertoire of movements, such as erect bipedalism across a range of substrates at various speeds and vertical climbing. Overall, six DOFs are a requirement for modelling mobility in fossil hominins, otherwise the resultant functionality of a given joint may be wrong.
We conclude that the likely maximum joint spacing/cartilage thickness of AL 288-1’s hip joint was 2.448 mm which is on par with allometric scaling assumptions (i.e., the smaller bodied AL 288-1 has a more cartilaginous hip joint than the larger bodied human and chimpanzee). Similar estimates were also generated from the single axis translational simulations, despite some implied functional limitations.
The important bit: we cannot ignore translational movement of the hip when estimating the motion-capability of extinct species!
Want to read more? See the paper or the projects update page of this website.
The Walking Hominins 