The Foot
Components of the Foot
Bones of the Foot
There are 26 bones in each foot, accounting for a total of 52. In the entire human body there are 206 bones, meaning that 24.24% of all the bones we have are in our feet. The shape of the bones in our feet accommodate a number of phenomenal functions. For example, the calcaneus has a smooth, rounded shape for rocking forward during locomotion. The talus has a small shelf that lets the tibia rest upon it. All of the tarsal bones of the foot and the ends of the metatarsals adjacent to them are shaped to allow for a locking motion during supination. The navicular in particular acts as a keystone when the foot is locked, allowing the tarsals and metatarsals to push into it from either side, creating a stable, powerful arch.
Joints of the Foot
There are 34 synovial joints in each foot, making a total of 68 between them. The whole body sports 360 joints in total meaning that 18.9% of the joints in the entire body are located in our feet. The job of a joint is to keep the surfaces of two adjacent bones a specific distance from one another as well as lubricate them so that they can glide over each other without causing friction. The interplay between the joints of our feet allows for smooth transitions between the locking and unlocking mechanisms of supination and pronation that our foot utilizes all day long.
Muscles, Tendons and Ligaments of the Foot
There are 29 muscles that act upon the foot. Ten of these muscles are extrinsic, starting somewhere above the ankle and then attaching to the foot. The other 19 are intrinsic, located directly in the foot. If there are 29 muscles, that means there are 58 tendons, as each muscle needs a tendon on both ends in order to connect their respective bones. There are 30 ligaments attaching the bones themselves to one another. All of these soft tissues together create a complex web that helps hold up the arch of the foot under stress at multiple different angles.
Anatomical Structures and Functions
Arches of the Foot
The various arches of the foot are supported by the tension of soft tissues. Most of the tissues in the foot are either tendons are ligaments, and are taut enough that they can resist our body weight pressing down upon them. These tissues are both intrinsic and extrinsic to the foot. Intrinsicly there are tissues like the spring ligament, the short and long plantar ligament and the plantar aponeurosis. The intrinsic tissues keep the bones of the foot from seperating from one another and are mostly made of ligaments. Some extrinsic muscles that support and stabilize the arch would include the tibialis anterior and posterior and fibularus longus. The extrinsic elements are more often made of muscle and tendons, providing support during active weight bearing such as walking or running. The tension that these soft tissues create, along with the the articulations that the bones of the foot have between one another, allow the arches of the foot to support forces that are many multiples past our body weight. While it could be argued that their are many minute arches throughout the foot, there are three core arches that are commonly recognized: The medial arch, the lateral arch and the transverse arch. While all three are significant in resisting forces and creating energy, the medial arch of the foot is a feature that sets us apart from all of the animal kingdom. The elasticity and tightness of the tissues in our foot create the medial arch, and it is the same resistant tissues that enable the foot to absorb shock and then recycle that shock as energy. The medial arch's shock absorption abilities occurs when walking, running or jumping while the foot is being loaded with weight. At his time, the medial arch "unlocks" and stretches in a motion called pronation, and then recycles the energy when the tension is released and as the muscles of the foot and ankle flex into supination.
Toe Splay
From the day we are born, the widest part of the human foot is meant to be from the hallux to the fifth phalange. If left untampered with, there is no reason why most of us shouldn't retain this shape for out entire lives. This natural splay of our toes provide fantastic levers for the arches of our feet, allowing the arches to lengthen in preparation for work and then press on the ground and squeeze. The clearest example of the benefits proper toe alignment provides is when observing individuals with fallen arche. Their condition is often accompanied by hallux valgus, as the fallen arch puts the foot into overpronation, pushing the big toe laterally. It is often hard to know if the hallux valgus condition is due to the fallen arch or if the fallen arch is due to the hallux valgus. What is certain is that when the the big toe is stuck in a lateral facing angle, it creates a vicious cycle of destabilization, as the muscles responsible for pulling the toe medially become weaker and weaker over time, and the development of bunions make it less and less possible to relocate the toe due to structural deformation. If the big toe is allowed to realign with the rest of the foot, the medial arch has a lever in which to push up off the floor, providing it with a much better biomechanical advantage.
Proprioception
Proprioception can be summarised as a combination of balance, coordination and timing. Every muscle in the body has special nerves called "mechanoreceptors". Whenever a muscle, tendon or ligament feels a change in it’s length or the tension, or a joint feels an increase in pressure, these special nerves report the change to the spinal cord. Because a change in length, tension or pressure in our soft tissues means that something is being moved out of place, then immediate action must be taken. The spinal cord does not even take the time to send these special signals to our brain for processing, and instead sends an automatic impulse to resist these changes to stabilize the bones and joints the tissue is attached to. This stabilization takes form either in a muscle flexing or relaxing to safely accommodate the motion taking place. This unconscious symphony allows us to perform motions, even simple, every day ones without having to think about each movement involved. When our foot has full range of motion between the large number of the joints, muscles, tendons and ligaments within it, then the timing and communication between them remain unhindered and can even improve over time. The proprioception we receive from our feet allows us to correctly distribute weight throughout our entire body, saving us energy and lowering the risk of injury.
Significant Movement Patterns of the Foot
The Windlass Effect
The foot has the ability to transform into a solid lever during landing or push off in order to receive our body weight and give our leg muscles a solid lever to push off of. This mechanism was researched by John Hicks, who noticed the arch of the foot became elevated when the toes were lifted into the air. This is because the tension in the soft tissues of the foot are so great, that when other tissues tried to stretch them, the bones are pulled closer together instead of the soft tissues lengthening further.
Inversion & Eversion
Inversion is the motion of pointing the plantar surface of the foot towards the mid-line of the body. This motion is often associated with ankle sprains, as this is the shape the foot will have when falling sideways during an ankle sprain. Eversion is the motion of pointing the plantar surface of the foot away from the mid-line of the body.
Dorsiflexion and Plantarflexion
While these are technically motions that are defined as movement at the ankle, the foot and toes will typically flex when pointed into plantarflexion and extend when put into dorsiflexion. Plantarflexion is associated with contraction and the phase of foot and ankle push off, while dorsiflexion is often associated with deceleration and loading of the foot and ankle complex.
Pronation & Supination
Supination & pronation can be thought of as the "locking and unlocking" of the foot. During supination, our ankle inverts and plantar flexes while the tibia externally rotates. During supination, the muscles of our foot flex and shorten, squeezing the bones of our arch together, increasing their stability. During pronation, our ankle everts, dorsiflexes while the tibia internally rotates. During pronation, the soft tissues of our foot lengthen and the foot widens to become a mobile adaptor, providing stability and creating tension that can be used as elastic recoil. Both pronation and supination occur all day long as we stand, walk and run. The degree to which an individual's foot remains in pronation or supination while at rest depends upon a number of factors, mostly having to do with the individual's posture and joint alignment. But even if they are prone to overpronation (often diagnosed as flat feet), when the feet are given space to move, they will supinate to a degree with each step the individual takes.
More to Read
Image Sources
bones - Mikael Häggström, Public domain, via Wikimedia Commons
foot - Public Domain
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