Ankle joint
The main articular structures of the ankle and foot include three important joints. These are the talocrural joint, the subtalar joint, and the transverse tarsal joint. Of particular note is that the talus bone plays a key mechanical role in all three of these major joints.
When examining the characteristics of the various joints formed by these bones, it is clear that the talus is a complex anatomical structure with approximately 70% of its surface covered by smooth articular cartilage tissue. Understanding the unique morphological features of these bones is an important basis for understanding the overall kinematic mechanisms of the ankle and foot.
Ankle movement
Two types of terminology are used to accurately describe the various movements of the ankle and foot, including fundamental and applied terminology. Fundamental terminology is used to describe the basic movements of the ankle and foot that occur at right angles to the three main axes of rotation.
These are dorsiflexion, extension, and plantar flexion in the sagittal plane around the medial-lateral axis of rotation; eversion and inversion in the forehead plane around the anterior-posterior axis of rotation; and abduction and adduction in the horizontal plane around the vertical (up-down) axis of rotation.
However, in practice, most movements in the ankle and foot occur around an oblique axis rather than these three basic orthogonal rotational axes, so these basic terms do not fully describe movement, especially at the three major joints of the ankle and foot.
To compensate for this limitation, a second terminology, applied terminology, has been developed to more accurately describe the complex movements of the ankle and foot. This is intended to describe movements that occur perpendicular to the oblique axis of rotation.
In this system, two main compound movements are defined: firstly, pronation is described as a combination of the elements of pronation, supination and dorsiflexion, and secondly, supination is defined as a combination of the elements of supination, vowelling and plantarflexion.
The orientation of the axis of eversion varies slightly at each major joint, but generally has a similar angle of inclination to that shown in the figure. The exact inclination of the axis of rotation at each major joint is discussed in detail in the following paragraphs.
Of particular note is that prone and backward rolls are often referred to as ‘triplanar motion,’ which can sometimes be misleading. The term triplanar simply means that the motion involves all three basic planes of motion, not that it has three degrees of freedom. In reality, spills and flips are single movements that occur in one plane of motion each.