Anatomy of the foot
The anatomy of the foot is composed of 26 bones, this consists of 7 tarsal bones, 5 metatarus bones and 14 phalanxes. The function the feet is to support our bodyweight and act as a lever to move our body forward when we walk. The body weight is mainly carried by the talus and calcaneus. The talus articulates with the distal ends of the tibia and fibula at the talocrural joint, which is also known as the ankle joint. This joint allows dorsiflexion and plantarflexion of the foot. The calcaneus forms the heel and supports the talus on its superior surface. The cuboid and the three cuneiform tarsals articulate with the proximal ends of the metarsals. The metatarsus is composed of metatarsal bones, it’s role is to support the body weight and hence why they have a short and thick structure. The big toes, also known as the hallux contains only two bones, the proximal and distal while the other four phalanges contain a middle part connecting the distal and proximal ends.
A lot of the muscles that move the foot and the toes originate in the lower anterior limb and their long tendons pass over the ankle and into the foot to insert into the toes to move them. The foot contains intrinsic muscles in four layers which are there for precision movements. These muscles are constantly contracting and relaxing while responding to dynamic changes so that the foot can be positioned on the surface of the ground when we walk. The ankle joint can be dorsiflexed and plantarflexed. The muscles responsible for dorsiflexion and toe extension originate in the anterior lower leg and not the foot. They include tibialis anterior, extensor digitorum longus, extensor digitorum brevis and extensor hallucis longus. The muscles pass over the ankle and foot and attach to the digits on the extensor surface with the dorsum of the toes. Fibularis longus and fibularis brevis muscles responsible are responsible for eversion of the foot and they can be found on the lateral side of the leg. Muscles responsible for plantarflexion and inversion of the foot can be found in the posterior compartment the lower limb. The three superficial muscles responsible for this movement are gastrocnemius, soleus and plantaris and they attach via the Achilles tendon.
The Achilles tendon is the largest, strongest and thickest tendon in the body. The other muscles that are deeper in the foot and enter the toes are flexor digitorum longus and flexor hallucis longus. Flexor hallucis longus and flexor digitorum have their tendons pass across the base of the foot splitting into 4 tendons so that the muscle of each toe can contract to invert the foot.
Ligaments around ankle and foot
Ligaments attach bone to other bones in order make them more stable structures. The medial side of the foot contains a very big ligament called the deltoid ligament, also known as the medial ligament. It is made up of four parts which are continuous with each other and therefore they can be seen as a single entity and a single ligament. The medial ligament attaches the medial malleolus of the tibia to the talus and calcaneal. The medial ligament is made up of the anterior tibiotalar, posterior tibiotalar, tibiocalcaneal, tibionavicular. This ligament stabilises the ankle joint on the medial side. It is going to stabilise the ankle joint during eversion and will also prevent subluxation which is dislocation of the ankle joint.
The lateral side of the foot does not contain a ligament which is as thick and strong. Three ligaments can be found on this side, and they include: anterior talofibular, posterior talofibular, calcaneofibular. The anterior talofibular and the calcaneofibular can be found at the front while the posterior talofibular can be found at the back. During a sprained ankle, the anterior talofibular and the calcaneofibular ligaments are most likely to become damaged while the posterior talofibular at the back of the ankle joint remains intact.
The foot also contains loose ligaments such as the extensor and flexor retinaculum on the dorsum and medial side of the foot to hold the tendons of the foot muscles in place. They are not like the articular ligaments which are short and pass over just one or two bones, they have a loose structure to allow structures such as arteries and nerves to pass underneath as well.