trabecular bone project

Background

Currently we can't directly test hypotheses about hominin running.  What is needed is a way to analyze fossil remains for evidence of habitual endurance running.  What if we could examine a foot or leg bone from a 1 million-year old human and determine whether it ran?  Because bone is a living tissue, adapting during life to use, certain bones may reflect habitual running.  Researchers already use some bone measures--especially in the "cortical" bone that makes up the long bones of the body-- to infer how active an individual was during life.  Trabecular bone- the porous bone found in joints and in the bones of the feet- is also gaining favor as a diagnostic tool.  It too adapts during life to the strains it experiences.  (To chew on all of the relevant background, see the full bibliography from my paper here.)

Human calcaneus with trabecular bone showing through the eroded cortical bone.

Reconstructed image stack from the first metatarsal of one of our subjects.  An individual trabecular strut- one of many such "trabeculae" comprising the bone-- is circled in yellow.

We set out with the following research questions: Do the calcaneus and first metatarsal (bones of the foot) reflect bone adaptation resultant from endurance running? And if so, can we identify these adaptive properties, in hopes of developing a model to test hominin fossils for evidence of running? 

Calcaneus (top right arrow) and first metatarsal (lower arrow).
Knowing that trabecular thickness, bone density and degree of aniostropy increase due to loading, we expected these variables to be higher in the bones of runners, and the calcaneus of forefoot runners to have the most robust trabecular measures of all.  (The Achilles tendon, which attaches to the calcaneus, exerts huge forces on the bone, and these forces are greater in forefoot runners.)  What we found may be the beginning of a new toolkit for testing hypotheses about hominin running.

Methods

In 2014 and 2015, under the tutelage of my UMass advisors and after convincing the UMass human subjects review board that I wouldn't maim, dehumanize, or (mostly) irradiate anybody, I collected data with Dr. Karen Troy at Worcester Polytechnic Institute.  This was to be my Master's project, but far from being just an exercise in learning to be an anthropologist and scientist (it was that too), it had the potential to actually inform science in a meaningful way.

A recruitment campaign netted us 19 test subjects: 13 runners, of whom 6 were forefoot strikers and 6 rearfoot strikers (see right) with one guy who switched up footstrike depending on pace.  Six were nonrunners-- our control group.  Most of the runners came to the UMass Biomechanics Lab where I fitted them with tracking markers and recorded their running stride with high-speed motion capture.  Mostly, this was to be darn sure of their footstrike method.

At the Biomechanics Lab, you are seen as nothing but a disembodied form of tracking markers.
Next, runners and nonrunners alike travelled to Worcester Polytech for a dose of radiation in Dr. Troy's high resolution peripheral computed tomography machine. (It scans and builds an image of the internal structure of the bone, measuring all sorts of trabecular properties along the way.)

Face blotted out to protect the innocent.
...We pointed the scanner to focus on the following regions of each bone:




...and used another computer program to reconstruct the images for further analysis:

calcaneus scan

1st metatarsal scan
The computer in the WPI lab has onboard software the computes and spits out data for the trabecular variables we wanted to measure.  Degree of anisotropy required using another program and significantly more user input.  At that point, all that was left to do was feed the data through a statistical program to analyze differences between testgroups....

Results and Conclusions
*embargoed while the paper undergoes peer review.




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