The arched structure of the foot consists of the medial longitudinal arch, the lateral longitudinal arch and the anterior transverse arch; with the longitudinal arches acting as pillars for the transverse arch that runs diagonally across the tarsometatarsal joints.
The lateral longitudinal arch is formed by the calcaneus, cuboid and fourth and fifth metatarsals. Compared to the medial arch, this arch has limited mobility and is relatively shallow.
The flexible medial longitudinal arch runs across the calcaneus to the talus, navicular, cuneiforms, and first three metatarsals.
At toe contact with the ground, this arch elongates to its maximum length, before shortening at mid-stance, then elongating slightly, followed by rapid shortening at toe-off.
Among the three arches of the foot, the medial arch plays a significant role in shock absorption upon contact with the ground. It achieves this by transmitting the vertical load on the foot through deflection of the arch, thereby lessening the impact on the foot as it hits the ground.
It is worth mentioning that while the medial longitudinal arch is adjustable, it is not built to make complete contact with the ground. The plantar calcaneonavicular ligament, or the ‘spring’ ligament, is responsible for restoring the medial longitudinal arch to its original position after elongation.
For patients with flat feet, however, this arch stretches out to an abnormal limit, flattening out completely on the ground during gait and resulting in a postural deformity of the foot.
The transverse arch is formed at the coronal plane of the foot by the metatarsal bases, the cuboid bone and the three cuneiform bones. When sufficiently supported by the interosseous, plantar and dorsal ligaments, this arch supports the forefoot during weightbearing activities, causing the metatarsals to spread out.
Together, these three arches coordinate to absorb the stress resulting from heel strike during gait, adapt to the ground during the stance phase and act like a rigid lever to assist the foot during push-off.
With a collapse of any of the foot arches, there is an imbalance in the way the body’s centre of mass is distributed over the leg, particularly over the centre of the foot that is anterior to the ankle, thereby increasing the stress placed on the feet and ankles.
This foot dysfunction ultimately manifests itself in the form of postural abnormalities which affect the overall balance and stability of the individual.
The intrinsic muscles of the foot, which originate on the heel bone, constantly work to stabilise the arches of the foot while regulating the rate of pronation and giving motion control to the foot.
Two groups of these muscles exist - the plantar group located on the sole of the foot, which stabilises the arch and controls movement of individual digits, and the dorsal group located on the dorsum of the foot which assists some of the extrinsic muscles in their actions.
Contrary to the common misconception that orthotics weaken the intrinsic muscles, the augmented calibration process at MASS4D® ensures that the resultant orthotic aids these muscles to work within their full range of motion, starting from the full resting point to full elongation and back to the original state of rest.
Optimal arthrokinematics is achieved through the optimal alignment of bones and ligaments, further promoting muscle strength and stabilising the arches of the foot in the process.
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