Articular Kinematics of the Transverse Tarsal Joint and the Medial Longitudinal Arch

Articular Kinematics

The kinematic characteristics of the transverse tarsal joint are best understood as an integrated motion mechanism encompassing both the rearfoot and midfoot. A detailed examination of active supination in a non-weight-bearing state, as shown in the illustration, provides a clear understanding of these complex motion patterns.

The tibialis posterior, which features multiple attachment points, serves as the key muscle driving supination of the foot. Due to the structural stability of the calcaneocuboid joint, the inversion and adduction of the calcaneus effectively pull the lateral column of the foot "beneath" the medial column. At this point, the talonavicular joint functions as the pivotal rotational center of these combined movements, while the contraction force of the tibialis posterior induces a precise spinning motion of the navicular bone and dynamically elevates the medial longitudinal arch of the foot.

During this movement, the concave shape of the navicular bone and the proximal portion of the spring ligament simultaneously rotate around the convex head of the talus. The biomechanics of pronation in a non-weight-bearing state can be understood by applying the aforementioned principles of supination in the opposite direction.

In pronation, the contraction force of the fibularis longus becomes the primary driving force, lowering the medial side of the foot while elevating its lateral side, altering the overall position and alignment of the foot. The kinematic analysis of supination and pronation described thus far primarily assumes a non-weight-bearing or suspended state of the foot. However, understanding the kinematic characteristics of the foot when it contacts the ground, as in gait, holds significant clinical importance.

The Medial Longitudinal Arch

The medial longitudinal arch and transverse arch of the foot are critical for determining structural stability and functional elasticity during weight-bearing activities. The talonavicular joint acts as the keystone of the medial longitudinal arch. This arch forms the characteristic concave "instep" along the medial aspect of the foot and serves as the primary load-bearing structure and an efficient shock absorption system. The skeletal components of the arch include the calcaneus, talus, navicular, cuneiforms, and the three medial metatarsals.

Without this arched structure, the abrupt impact forces generated during high-intensity activities such as running would exceed the physiological load-bearing capacity of bone tissue, potentially causing severe problems. Additional anatomical structures supporting the function of the medial longitudinal arch include the plantar fat pad, the sesamoid bones at the plantar base of the hallux, and the superficial plantar fascia, which attaches primarily to the thick dermal layer to effectively dissipate shear forces.

The medial longitudinal arch and its associated connective tissues are optimized for providing structural support under low-load conditions, such as static standing. However, in dynamic activities where the load and stress on the foot significantly increase—such as tiptoeing, walking, jumping, and running—active muscle engagement plays a crucial role in reinforcing the function of the medial longitudinal arch.