Classification of Joints in the Foot and Ankle

The ankle joint is made up of distal ends of the tibia and fibula, which fits over the top portion of the talus in the form of a socket.

This joint plays an important role in the movement of the body in the sagittal plane and during the process of walking.

One of the other critical functions of the ankle joint is its capacity for undergoing transverse plane motion.

This was proven by a study conducted by Lundberg et al., which found an average of 8.4° of transverse plane ankle motion during 30° of external leg rotation.

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In another study published by Nester et al., kinematic data for twenty-five subjects was calculated. It was found that the ability of the ankle joint to move in the transverse plane, allows the leg and proximal structures to rotate in the transverse plane, as the foot remains in a fixed transverse plane position on the floor.

According to a comprehensive study carried out by Lundgren et al, the total range of motion at the talonavicular joint during walking was reported as 8.4° (1.1°), 14.9° (6.1°), 16.3° (6.5°) in the sagittal, frontal and transverse plane respectively.

Besides providing a clear description of in vivo rear, mid and forefoot kinematics during walking, this study also showed the complexity of the foot and the importance of the less obvious joints distal to the rearfoot.

The deltoid and lateral ligaments of the ankle are critical in guiding motion at the ankle and rearfoot complex.

Leardini et al. were successful in demonstrating how the calcaneofibular and tibiocalcaneal ligaments together with the articular surfaces guide ankle passive motion; with both ligaments showing near-isometric pattern of rotations.

While the foot consists of a number of joints, the most impactful are the subtalar and midtarsal joints, which allow for the inversion and eversion of the foot.

The subtalar joint complex has been the subject of considerable discussion in the past. Regarding the orientation of this complex, the subtalar joint is unable to move in only one of the anatomical planes at a time, as it consists of a number of discrete axes of rotation, which together form a bundle of joint axes that pass through the talocalcaneal joint.

These joint axes have been determined to run in an oblique infero-postero-lateral to supero-antero-medial direction.

Evert Van Langelaan, in his detailed work on subtalar and midtarsal joint kinematics, established that the midtarsal joints do not consist of two fixed simultaneously-occurring axes, i.e. the longitudinal and oblique midtarsal joint axes.

Through his research, he proved that the talonavicular and calcaneocuboid joints have multiple joint axes that move in space relative to these bones, as the subtalar joint pronates and supinates.

The considerable freedom of movement of these joints is due to the ball and socket nature of the talonavicular joint, rather than a hinge function as was previously stated by most researchers.

A better understanding of foot and ankle biomechanics can have far-reaching consequences on the designing of orthoses and in the prevention of foot and lower limb problems.

The complex nature of this mechanism further reinforces the fact that in order to achieve significant results in the treatment of lower limb pathologies, it is imperative to consider the dynamics of the foot of each patient to produce orthotics that can provide for specific corrections, asymmetrical posting and lifting, and support for any unusual and anomalous anatomical problems.

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