When a patient dorsiflexes the foot, what muscles are involved and what changes occur in the lower limb

Word count 890 excluding references

In this essay the author will take a brief look at the structure of the foot and then describe the muscles involved in dorsiflexion of the foot and the changes that occur in the lower limb.
The foot can be divided in to three parts; the hindfoot, midfoot and the forefoot. The hind foot is composed of the talus (ankle bone), the calcaneus (heel bone) the tibia and the fibula, the long bones in the lower leg. The tibia and fibula are connected to the top of the talus to form the ankle. The calcaneus is connected to the talus at the subtalar joint. The calcaneus is the largest bone in the foot and it is cushioned by a layer of fat. The midfoot is made up of the cuboid, navicular and three cuneiform bones. These form the arches of the feet that serves as a shock absorber. The midfoot is connected to the hindfoot and forefoot by muscles and the plantar fascia. The forefoot is composed of five toes and corresponding five proximal long bones (metatarsals). The big toe has three phalanges, and the other toes have three phalanges each.
The ankle is a synovial hinge joint resembling a mortice joint (as in carpentry) allowing two movements; plantar flexion, where the foot is pointed down and dorsiflexion where the foot toes are pointing towards the shin. . “Four important ligaments strengthen this joint; the deltoid and the anterior, posterior, medial and lateral ligaments” (Waugh & Grant 2014). In dorsiflexion the surface of the talus slides backwards into the mortice formed by the malleoli and the joint becomes close-packed, particularly as the part going in to the mortice is increasingly wider. In plantar flexion the talus slides forwards out of the mortice and the movement of the foot becomes freer. In the foot there are a number of other synovial hinge joints; the joints between the tarsal bones, between the tarsal and metatarsal bones, between the metatarsals and the proximal phalanges and between the phalanges. Movements are produced by muscles in the leg and long tendons that cross the ankle and the muscles in the foot.
In dorsiflexion of the foot there are three anterior skeletal muscles responsible for this movement. The tibialis anterior, which is the prime mover also known as the agonist, in dorsiflexion of the foot. The extensor hallucis longus and the extensor digitorm longus muscles are synergists or muscles that assist the prime mover in its role.
The tibialis anterior (The prime mover) originates in the proximal two-thirds of the lateral surface of the tibia and the interosseous membrane and is inserted at the medial and plantar aspects of the medial cuneiform and the base of the first metatarsal. The extensor halluces longus (synergist) originates as a muscle in the middle section of the fibula and adjacent interosseous membrane and ends as a tendon is inserted at the dorsal base of the distal phalanx of the big toe. It is the prime mover in dorsiflexion of the big toe and assists in dorsiflexion of the foot. The extensor digitorum longus (synergist) originates in the lateral area of the tibia, proximal two-thirds of the medial surface of the fibula and adjacent interosseous membrane. It splits in to four tendons that attach to the proximal base of the dorsal surface of the middle and distal phalanges. This muscle is the prime mover in dorsiflexion of the toes but assists in the dorsiflexion of the ankle.
Each of these anterior muscles are innervated by the deep peroneal nerve. The nerve receives stimulation from the central nervous system to contract (shorten) during dorsiflexion. “Muscle contraction is an active process and requires energy (derived from glucose) in the form of adenosine triphosphate (ATP)”. (O’Callaghan M 2013). ATP “is molecular store of chemical energy for chemical reactions” (Waugh & Grant 2014). The muscles relax when stimulation stops therefore returning to original length. In order for muscles to operate at optimum levels there has to be a good blood supply in order to provide oxygen, nutrients, calcium and also to remove waste materials.
There are also antagonist muscles involved in resisting dorsiflexion and reversing it when it changes direction to regular posture or plantar flexion. These muscles are found at the back of the lower leg; the gastrocnemius, soleus and the tibialis posterior. When the foot is in dorsiflexion, the anterior tibialis and assisting muscles are contracted while the antagonist muscles are stretched in resisting the movement. “This (also) helps to activate the calf muscle pump, which plays an important role in propelling blood away from the lower leg towards the heart. The process of dorsiflexion stretches the calf muscle, which results in a contraction of the posterior compartment. This increases the pressure within the vein, opens the superior one-way valve and forces the venous blood upwards”. (Garcia & Lund 2004).
In conclusion it can be seen that skeletal muscles do not work alone but work in pairs, the agonist and the antagonist. For muscles to work effectively and to remain healthy they need a good blood supply in order to receive required nutrients, calcium, and oxygen and to remove waste materials. In dorsiflexion of the foot the anterior muscles originate within the leg therefore contraction takes place in the anterior aspect of the lower limb. Dorsiflexion also affects the posterior muscles which are antagonists to the anterior muscles. These posterior muscles stretch as the anterior muscles contract and the posterior muscles relax when the anterior muscles return to normal length.

References 1. Garcia M.C. & Lund K (2004). Venous ulcers and motorized ankle dorsiflexion: an introduction to a new approach. http://www.worldwidewounds.com/2004/june/Garcia/Motorised-Dorsiflexion.html accesses 21/07/2015 2. O’Callaghan M. (2013) Leaving Certificate Biology Plus. Dublin. The educational Company of Ireland 3. Waugh A. & Grant A (2014). Ross and Wilson Anatomy and Physiology in Health and Illness 12th edition. UK. Churchill Livingstone Elsevier