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The Neandertal (Krapina and Regourdou 1), fossil modern human (Chancelade 1) and extant human patella: an insight from inside

Evolutionary endostructural patterns of the cortical and cancellous tissues of the postcranial skeleton are commonly investigated for inferring functional behaviours in extinct hominin taxa and past human populations. Information on the endostructural arrangement of the patellar bone has the potential of revealing individual- and/or taxon-specific aspects of the knee biomechanics. However, evidence on its inner conformation extracted from human fossil specimens is nearly non-existent. The present pilot study aims at characterising the endostructural pattern of two Neandertal (from Krapina, Croatia, and Regourdou, France) and one anatomically modern fossil human (from Chancelade, France) adult patellae and to compare their signal with the recent human condition. In the context of the gracilisation trend of the human skeleton occurred from the late Pleistocene, we expect (i) the two Neandertal patellae showing a higher amount of cortical bone compared to the fossil modern and the recent human conditions, (ii) the fossil modern patella showing a higher amount of cortical bone compared to the comparative sample, (iii) the cancellous network being relatively homogeneous between the two Neandertal individuals but distinguishable from that of the fossil modern human representative and of the comparative sample, and that (iv) the structural organisation revealed by the fossil modern patella is distinguishable from the recent human condition. For assessing the endostructural organisation of the selected patellae, we used non-invasive techniques of high resolution virtual imaging. The results do not support the first hypothesis, as marked differences have been found between the two Neandertal specimens. The second hypothesis is supported for the anterior surface, but not for the posterior surface. The third hypothesis is supported for the superior and the lateral regions of the patellar bone but for the inferior and medial portions. Finally, the fourth hypothesis is supported, but the cancellous organisation of the two Neandertal representatives is closer to the extant human pattern than to the Magdalenian specimen. Despite the generalised lack of comparable information from the human fossil record, we consider the present results of potential interest for future research of paleobiomechanical, paleobiological, and perhaps taxonomic interest, on the evolutionary structure of the human knee joint.

knee joint, patella, endostructure, biomechanics, Neandertals, anatomically modern fossil humans

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