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Modeling Complex Cranial Joints in Varanus exanthematicus
Author(s) -
Wilken Alec T.,
Middleton Kevin M.,
Sellers Kaleb C.,
Cost Ian N.,
Davis Julian L.,
Holliday Casey M.
Publication year - 2017
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.31.1_supplement.577.5
Subject(s) - joint (building) , anatomy , ligament , amniote , synovial joint , cartilage , biomechanics , morphology (biology) , finite element method , biology , structural engineering , articular cartilage , vertebrate , osteoarthritis , medicine , paleontology , biochemistry , alternative medicine , pathology , gene , engineering
In contrast to humans and other mammals which have relatively few mobile cranial joints, most lizards exhibit cranial kinesis, intracranial movement between bones, which they inherited from their amniote ancestors. Although the tissue‐level structure of kinetic joints has been described, how these joints are loaded during feeding remains relatively poorly known. Finite element analysis previously has been used to estimate joint loading; however, these studies have not modeled mobile joints, instead fusing bones across joints, creating a solid model. We have developed a new method of modeling mobile cranial joints, in which joint spaces are filled with materials that have the properties of cartilage, ligaments, and other tissues that are known to contribute to joint structure. Because their skulls house many different types of structurally and compositionally different joints, ranging from sutural to synovial, lizards make excellent model organisms for studying the relationship between the composition and loading of cranial joints. We created a 3D finite element model of the cranium of an individual of Varanus exanthematicus , a species with intermediate levels of kinesis for which comparative feeding data is available. Intracranial joints were modeled as flexible interfaces between bones and material properties of those joints could be assigned independently. Muscle force magnitudes were calculated from physiological cross‐sectional area estimates and oriented toward mandibular attachment sites. These forces and orientations mimicked feeding behavior. For each simulation, we changed the properties of the joint material to (1) cartilage, (2) ligament, and (3) bone, which represents a fused morphology. Comparisons among these models show lower overall strain energy when joints are modeled using ligament and cartilage, whereas joints modeled with bone showed areas of high stress concentrations. Modeling joints as non‐bony soft‐tissues produced deformations that more closely approximated in vivo feeding kinematics. This concordance affirms the model's ability to recreate feeding mechanics; therefore, the methods used to develop the varanid model can be used to more accurately model the feeding mechanics of fossils, which cannot be directly checked against in vivo feeding kinematics. Support or Funding Information National Science Foundation IOS 1457319