Arches of the foot and ligamentous apparatus
Anatomically, one longitudinal and two transverse arches are distinguished on the plantar surface.
The longitudinal arch has a complex structure and is divided into two parts:
- Lateral part: performs predominantly a weight-bearing function. It is formed by the calcaneus, cuboid, and the IV and V metatarsal bones.
- Medial part (spring): provides shock absorption during walking. It comprises the talus, navicular, three cuneiform bones, and the I–III metatarsal bones.
A crucial role in strengthening the arched structure of the foot is played by the long plantar ligament (lig. plantare longum). It originates from the inferior surface of the calcaneus and extends anteriorly, supporting the longitudinal arch.
Plantar aponeurosis and fasciae
The superficial fascia is absent in this area. The main covering structure is the plantar aponeurosis (aponeurosis plantaris), which is a thickened deep fascia in the middle part of the sole.
- In the tarsal region: the aponeurosis has a particularly dense structure. At this site, it gives rise to a portion of the fibers of the flexor digitorum brevis.
- On the sides: the structure thins out and attaches to the tarsal bones, and distally to the I and V metatarsal bones.
- Distal region: at the level of the metatarsus, the aponeurosis divides into 4–5 slips that cover the tendons of the digital flexors. These slips are securely connected to each other by transverse fasciculi (fasciculi transversi).
Fascial compartments of the sole
From the edges of the plantar aponeurosis, two intermuscular septa (medial and lateral) extend deeply. They divide the subaponeurotic space into three fascial compartments:
- Medial compartment: intended for the muscles of the great toe (hallux).
- Middle compartment: contains the superficially located flexor digitorum brevis (m. flexor digitorum brevis), as well as other muscles and tendons of the long flexors.
- Lateral compartment: houses the muscles of the little toe (V digit).
Boundaries of the lateral compartment:
- Inferiorly and laterally: deep fascia.
- Medially: lateral intermuscular septum.
- Superiorly: cuboid and V metatarsal bones.
The lateral compartment contains: the abductor digiti minimi muscle (m. abductor digiti minimi, forming the lateral border of the foot), the flexor digiti minimi brevis, and the opponens digiti minimi.
Commissural apertures and calcaneal canal
Commissural apertures are localized between the longitudinal slips of the plantar aponeurosis and the transverse fasciculi. They are filled with adipose tissue; through them, the tendons of the lumbrical muscles pass, and the common plantar digital vessels and nerves emerge (aa. et nn. digitales plantares communes). Clinically, this is an important site: through these apertures, the subcutaneous tissue communicates with the middle fascial compartment, serving as a pathway for the spread of purulent processes.
In the proximal part of the medial compartment lies the calcaneal canal (canalis calcaneus). Its walls are formed by the calcaneus and the abductor hallucis muscle. The lateral plantar neurovascular bundle and the tendon of the long flexor pass through it from the malleolar canal into the middle plantar compartment.
Neurovascular bundles and innervation
The neurovascular bundles are formed in the medial malleolar canal by the division of the posterior tibial artery and the tibial nerve (n. tibialis). They divide into medial and lateral branches. The medial bundle is located within the medial intermuscular fascial septum.
Zones of cutaneous innervation:
- Calcaneal region: tibial nerve.
- Lateral margin of the foot: lateral plantar nerve.
- Medial margin and center: medial plantar nerve.
- Medial surface (narrow strip): saphenous nerve (n. saphenus).
Motor innervation: Branches of the lateral plantar nerve supply the quadratus plantae, all interosseous muscles, and the two lateral lumbrical muscles. The skin of the V digit and the lateral side of the IV digit is innervated by the proper plantar digital nerves. Comparative anatomy demonstrates that the distribution of these nerves in the foot is analogous to the course of the median and ulnar nerves in the hand.
Briefly: answers to topical questions
Which muscles are innervated by the motor branches of the lateral plantar nerve?
The motor branches ofalu the lateral plantar nerve supply the muscles of the little toe, interosseous muscles, as well as certain muscles of the central and medial groups. These include:
- Quadratus plantae muscle (m. quadratus plantae);
- Two lateral lumbrical muscles (mm. lumbricales);
- All interosseous muscles (mm. interossei);
- Muscles of the V digit (little toe);
- Adductor hallucis muscle (m. adductor hallucis).
Which specific muscles and tendons are located in the middle fascial compartment of the sole?
The middle fascial compartment of the sole contains the muscles of the central group and flexor tendons. The contents of the compartment include:
- Flexor digitorum brevis (m. flexor digitorum brevis);
- Tendons of the flexor digitorum longus (m. flexor digitorum longus) with lumbrical muscles;
- Quadratus plantae muscle (m. quadratus plantae);
- Adductor hallucis muscle (m. adductor hallucis);
- Plantar interosseous muscles.
What are the boundaries of the medial fascial compartment of the sole?
The boundaries of the medial fascial compartment of the sole are formed by fasciae, septa, and bones of the foot. They include:
- Inferiorly and medially — deep fascia (fascia propria), which is a continuation of the thinned plantar aponeurosis;
- Laterally — medial intermuscular septum (septum intermusculare mediale);
- Superiorly (in the tarsal region) — navicular and medial cuneiform bones;
- Superiorly (in the metatarsal region) — I metatarsal bone.
What passes through the calcaneal canal?
Through the calcaneal canal (canalis calcaneus), neurovascular structures and tendons pass from the malleolar canal into the middle plantar compartment. It contains:
- Medial neurovascular bundle;
- Lateral plantar neurovascular bundle;
- Tendon of long extensor of toes.
Furthermore, purulent processes can spread from the leg to the sole via the calcaneal canal.
To understand foot innervation, always draw a parallel with the hand: the medial plantar nerve branches like the median nerve in the hand (innervating the greater part), while the lateral plantar nerve acts like the ulnar nerve (supplying the little finger and adjacent areas).
Class and exam questions
Which structure plays the main role in strengthening the longitudinal arch of the foot?
A crucial role is played by the long plantar ligament (lig. plantare longum), which originates from the inferior surface of the calcaneus.
How many fascial compartments are distinguished in the sole?
Three fascial compartments are distinguished: medial (muscles of the hallux), central, and lateral (muscles of the little toe). They are separated by intermuscular septa extending from the plantar aponeurosis.
What is the clinical significance of the commissural apertures?
Through these apertures, the subcutaneous adipose tissue communicates with the central fascial compartment, creating an anatomical pathway for the spread of purulent processes.
Where is the medial neurovascular bundle located?
The medial neurovascular bundle lies within the medial intermuscular fascial septum of the sole.
What else to study on this topic
- Topography of the transverse section of the foot at the tarsal level (relationships between muscles and bones)
- Detailed structure of the central fascial compartment and the course of the long flexor tendons
- Walls and contents of the medial malleolar canal in relation to the sole
- Muscles of the lateral fascial compartment of the sole
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