Abstract
Orientation of the subtalar joint axis dictates inversion and eversion movements of the foot and has been the focus of evolutionary and clinical studies for a number of years. Previous studies have measured the subtalar joint axis against the axis of the whole foot, the talocrural joint axis and, recently, the principal axes of the talus. The present study introduces a new method for estimating average joint axes from 3D reconstructions of bones and applies the method to the talus to calculate the subtalar and talocrural joint axes. The study also assesses the validity of the principal axes as a reference coordinate system against which to measure the subtalar joint axis. In order to define the angle of the subtalar joint axis relative to that of another axis in the talus, we suggest measuring the subtalar joint axis against the talocrural joint axis. We present corresponding 3D vector angles calculated from a modern human skeletal sample. This method is applicable to virtual 3D models acquired through surface-scanning of disarticulated ‘dry’ osteological samples, as well as to 3D models created from CT or MRI scans.
Highlights
The average axis of rotation of the talus over the calcaneus at the subtalar joint (STJ) has long been the focus of evolutionary studies (Elftman and Manter, 1935; Gebo, 1992, 1993; Lewis, 1980, 1989; Morton, 1922, 1924, 1927) and clinical studies (Beimers et al, 2008; Manter, 1941)
For estimating the talocrural joint (TCJ) axis from the trochlea surface morphology, we found that sphere fitting to the medial and lateral half of the trochlea facet was the most reproducible method as each half can be defined as the facet surface between the central trochlea groove and the medial or lateral rim (Fig. 2)
There are clear similarities between the STJ axes calculated here (Fig. 3A) and those calculated from the in-vitro studies of Beimers et al (2008) (Fig. 3B), Manter (1941) (Supplementary Fig. 1) and Nester (1998) (Supplementary Fig. 2), suggesting that the method for defining the STJ axis introduced in the present study is accurate
Summary
The average axis of rotation of the talus over the calcaneus at the subtalar joint (STJ) has long been the focus of evolutionary studies (Elftman and Manter, 1935; Gebo, 1992, 1993; Lewis, 1980, 1989; Morton, 1922, 1924, 1927) and clinical studies (Beimers et al, 2008; Manter, 1941) This is because it has undergone realignment in modern humans, compared to the STJ axes in non-human primates and is not well defined clinically (Beimers et al, 2008; Fournol, 1999).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
