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Joint mechanics and inertia of the forelimb in extant equids as an initial step towards testing hypotheses on the evolution of monodactyly

Boek - Dissertatie

Members of the Equidae family, belonging to the Perissodactyla (odd-toed ungulates), underwent a strong digit reduction in both fore- and hindlimbs. The number of functional digits reduced to one (monodactyly). The driving forces behind the digit reduction within the Equidae are still unknown. Various hypotheses exist regarding possible selection pressures. It is currently believed that monodactyly is likely a result of multiple driving forces instead of just one main driving force. (Musculo)skeletal models of different representatives of the Equidae can be used to predict the locomotor performances (e.g. maximal speed and cost of transport) of (fossil) species in order to test hypotheses regarding the evolution of monodactyly from a locomotor perspective. Models are constructed using virtual representations of the skeletal system and biomechanical properties obtained from extant analogues. The aim of this thesis was to obtain joint constraints and inertial properties of the forelimb of extant equids which could be implemented in to the (musculo)skeletal models. By including joint constraints, the locomotion simulations will be within a species natural movement range. In this thesis the studied joint constraints of the different equine forelimb joints were: the number of rotational degrees of freedom, the range of motion, the coupling between rotational degrees of freedom and the helical axis. Additionally, the inertial properties of the forelimb segments were also measured. They are needed in order for the model to accurately simulate the movement of the segments. Our results showed that for the horse as a species, all forelimb joints displayed out of sagittal plane motion. For the elbow, fetlock and distal joints a clear coupling between rotational degrees of freedom was observed. For the helical axis, some properties of the different forelimb joints changed significantly with joint angle. Size only had a significant effect on a few of the helical axis properties of the different forelimb joints. The inertial properties did not differ between the three horses, donkeys and zebras for all forelimb segments except for the hoof. The three species used in this study did differ significantly in forelimb proportions. The results of the different joint constraints and inertia of the forelimb studied in this thesis should be taken into account when constructing (musculo)skeletal models of different monodactyl equids. This thesis provides the first step in testing hypotheses regarding the digit reduction within the Equidae using (musculo)skeletal models.
Aantal pagina's: 234
Jaar van publicatie:2020
Trefwoorden:Doctoral thesis
Toegankelijkheid:Open