Introduction Joint Facet Tropism Was Previously Defined As the Difference
1 Introduction 2 Joint facet tropism was previously defined as the difference between right and left 3D orientation of the facet-joint 3 (Brailsford, 1929). Additionally, spine joints morphology (i.e. surface geometry) has been also shown to be of 4 clinical relevance while possibly determining degenerative processes (e.g. osteoarthritis, degenerative 5 spondylolisthesis) or injury mechanisms of the spine (Liu et al., 2017). Tropism together with facet 3D orientation 6 have been proposed as factors likely associated with laterality of specific diseases in both the lumbar spine (Alonso 7 et al., 2017; Gao et al., 2017; Kalichman et al., 2009) and the cervical spine (Rong et al., 2017b; Xu et al., 2016, 8 2014). However, considering the costovertebral joint complexes which are involved in both respiratory function 9 (Cappello and De Troyer, 2002) and thoracic spine stability (Brasiliense et al., 2011; Liebsch et al., 2017; Oda et 10 al., 1996; Takeuchi et al., 1999; Watkins et al., 2005), it is questionable how tropism could similarly affect costal 11 facets, but literature concerning costal facets remains qualitative (Drake et al., 2010; Moore et al., 2010; Struthers, 12 1874). In addition, costal facet geometry may partly explain the variability in rib motion during breathing 13 movement (Beyer et al., 2016, 2015). Finally, since the costal facets are also related to the orientation of the 14 transverse processes (Bastir et al., 2014; Gray et al., 2005) measurements of 3D morphometric features of both 15 vertebrae and costal facets can contribute to the understanding of functional and clinical aspects of the rib/vertebra 16 relationship.
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