Joints must create mobility between skeletal elements while maintaining enough stability to remain articulated. Too stable and they cannot move, too mobile and they fall apart. Over the past 500 million years of vertebrate evolution (Askary et al., 2016; Haines, 1942a), this balancing act has generated an extraordinary diversity of sizes and shapes of articular surfaces, arrangements of soft tissues that bind them, and motions prevented or permitted. Therefore, when exploring the form–mobility relationship, we have tandem objectives – to ask how articular structures prevent motion, and to take on the opposite perspective and ask how they allow it.

We can make progress towards these goals by teasing apart how different articular structures such as ligaments, cartilage, muscle and bone interact to shape mobility. Computational analyses of joint mobility offer opportunities to visualize how interactions between bony surfaces prevent certain joint configurations, formalize and test our assumptions about what characteristics of articulation make a joint configuration possible in life, and even experimentally modify morphology and assess the influence of introducing or eliminating structures (e.g. Brocklehurst et al., 2022; Demuth et al., 2020; Hammond et al., 2016; Herbst et al., 2022b; Jones et al., 2021; Fahn-Lai et al., 2018; Mallison, 2010a,b; Manafzadeh and Gatesy, 2021; Lee et al., 2018; Molnar et al., 2021; Nyakatura et al., 2015; Pierce et al., 2012; Regnault and Pierce, 2018; Richards et al., 2021; Wiseman et al., 2022; for a review, see Manafzadeh and Gatesy, 2022). To investigate the constraints imposed by articular soft tissues, we can supplement virtual analyses with laboratory measurements of mobility from intact (e.g. Akhbari et al., 2019; Hammond, 2014; Hammond et al., 2017; Manafzadeh, 2020; Manafzadeh et al., 2021) and serially dissected joints (e.g. Arnold et al., 2014; Cobley et al., 2013; Crisco et al., 1991; Hutson and Hutson, 2012, 2013, 2014, 2015a,b, 2018; Kambic et al., 2017a,b; Herbst et al., 2022c; Manafzadeh and Padian, 2018; Martin et al., 2008), bearing in mind the concomitant loss of physiological realism when reducing them to subsets of their parts.

Once measurements of mobility are gathered and related to morphology within individual joints, we can also view these data within the context of entire organisms and evaluate how anatomical connections between or among joints – another aspect of their form – may create coordinated, dynamic changes in mobility during life. Whereas posturally driven differences in the mobilities of joints linked by biarticular muscles may be relatively simple to characterize (e.g. Nonaka et al., 2002; Okada et al., 1996), those among joints contributing to complex multi-bar systems (e.g. Bhullar et al., 2016; Holliday and Witmer, 2008; Lemberg et al., 2021; Olsen et al., 2017) will require more involved, network-based consideration (see Olsen, 2019). As the relationship between form and mobility becomes clearer, analyzing our findings within a comparative framework will empower us to develop a mechanistic, predictive and broadly transferable understanding of how differences in joint anatomy directly cause differences in potential motion.