The (intrinsic) muscles of the foot arise from and insert onto the foot itself and control individual movements of the digits.
There are 20 intrinsic foot muscles and they are divided into three different aspects:
- Plantar aspect (14 in number)
- Dorsal aspect (2)
- Intermediate (4)
Plantar aspect
Muscles in the plantar aspect of the foot are organized in four layers (first to fourth) within four compartments. They generally act as one group to support the stance by maintaining the arches of the foot.
First layer
The first layer is the most superficial and is divided into three compartments. It is located deep to the plantar aponeurosis. It is composed of the most medial abductor hallucis, flexor digitorum brevis, and abductor digiti minimi being the most lateral muscle.
Abductor hallucis
The abductor hallucis muscle is a fusiform muscle spanning between the calcaneus and the proximal part of the first toe.
- It originates from the medial process of the calcaneal tuberosity and neighboring borders of the flexor retinaculum and plantar sheath, inserting as a tendon on the medial border of the base of the proximal great toe and on the medial sesamoid bone.
- The abductor hallucis muscle is most active during the late (push-off) phase of stance as it acts to stabilize the foot. It abducts and flexes the great toe as well as pulling the lateral four metatarsals towards it. This muscle also contributes to a soft tissue swell on the medial foot.
Flexor digitorum brevis
The flexor digitorum