Combined Action of the Sub-Navicular Joint and the Transverse Tarsal Joint and Their Functional Significance

Combined Action of the Sub-Navicular Joint and the Transverse Tarsal Joint and Their Functional Significance

In a non–weight-bearing state—when no load is applied to the foot—the eversion movement causes the plantar surface to twist outward, while the inversion movement twists it inward in a simple, isolated manner. However, once weight is applied during the stance phase of gait, these movements become considerably more complex.

At that time, with the calcaneus remaining relatively fixed, the lower leg and the navicular execute precise rotational movements in the sagittal, frontal, and horizontal planes. This intricate biomechanical mechanism is achieved through the close, harmonious interaction of the sub-navicular joint, the transverse tarsal joint, and the medial longitudinal arch—a process that naturally occurs in a healthy foot.

A closer examination of healthy foot biomechanics reveals that the medial longitudinal arch dynamically changes its height throughout the gait cycle. Specifically, during the stance phase, as weight-bearing gradually increases, the arch slightly lowers.

Various anatomical structures that control the descent of the arch work together to effectively distribute and absorb the localized stresses caused by the progressive compression of the foot. Although not conclusively demonstrated under every condition in controlled studies, this shock absorption mechanism is widely recognized as playing a crucial role in protecting the foot and lower limb from stress-induced damage.

During the first 30–35% of the gait cycle, the sub-navicular joint performs an eversion (lateral deviation) movement, providing the necessary flexibility to the midfoot (Figure B). In the latter part of the stance phase, as the sub-navicular joint transitions into an inversion position, the rearfoot becomes a rigid structure, causing the medial longitudinal arch to rise. This structural stability prepares the foot to effectively handle the substantial loads encountered during the push-off phase of walking.

The foot’s unique ability to repeatedly transition—from a flexible, shock-absorbing structure to a rigid, lever-like structure with each gait cycle—is one of its most important and clinically significant characteristics. In this process, the sub-navicular joint serves as the key element in predominantly regulating the inversion and eversion kinematics of the foot.