Thumb opposition: its definition and my approach to its measurement

The trapeziometacarpal (TMC) joint allows movement in extension/flexion (alternatively termed radial abduction/adduction) in the frontal plane; abduction/adduction (alternatively, antepulsion/retropulsion) in the sagittal plane; and supination/pronation (rotation around the longitudinal thumb axis) (Figure 1). The first two are angular movements and the third is an axial rotation. I prefer to use the terminology extension/flexion and abduction/adduction for movements in the frontal and sagittal planes, and not those in brackets. Nevertheless, both are used by different authors. Circumduction is the path followed by the thumb in movement from full supination of 30 (reposition); to neutral rotation of 0 when the thumbnail is at 90 to the frontal plane with 20 of extension and 30 of abduction (neutral position); to full pronation of 90 with the thumbnail parallel to the frontal plane of the palm (opposition) (Figure 1).