This is a Y-shaped band draped across the dorsum of the foot.
The stem of the Y is attached to the lateral surface of the calcaneus; one limb is extended and attached to the medial malleolus; the other dips down the medial border of the foot, attached to the plantar aponeurosis at the sole of the foot.
Lateral side of the ankle:
3. Superior peroneal retinaculum - bridges the gap between the lateral malleolus and calcaneus.
4. Inferior peroneal retinaculum - smaller reinforcing band attached to the peroneal tubercle of the calcaneus, extending over the tendons of the peroneal muscles to join the attachment of the inferior extensor retinaculum at the lateral surface of the calcaneus.
Medial side of the ankle:
5. Flexor Retinaculum [ligamentum laciniatum] - strong band that bridges the medial concavity of the calcaneus, attached to the medial malleolus and to the medial tubercle of the calcaneus.
Superficial Group “Triceps Surae Muscle ”
Gastrocnemius – its two heads join to form a single belly which narrow to its tendon at about the middle of the leg.
Origins: medial and lateral head, from the corresponding femoral condyles.
Insertion: the “calcanean tendon” which is attached to a small area at the postero-inferior part of the calcaneus where a small bursa separates it from the bone.
Plantaris - small short muscle with a long tendon; arising from the lateral condyle of the femur, deep to the lateral head of the gastrocnemius and soleus muscles descending along the medial border of calcanean tendon joining it to its attachment.
Soleus – paddle-shaped muscle deep to the gastrocnemius; its fibers joining the calcanean tendon, which may also be called “ tendon of Achilles ”.
Origins: popliteal [oblique] line of the tibia; and proximal third of the fibula.
[Note the passage of the tibial n.v.s. between the separated origins of this muscle; thus enabling them to descend deeper into the posterior compartment of the leg.]
The Triceps Surae or Calf Muscles are the principal plantar flexors of the foot [ankle].
This action is clearly demonstrated when one stands on tiptoe. Moreover, aside from the primary function, the gastrocnemius may also help in flexing the leg.
Flexor Digitorum Longus – the medial [intermediate] muscle.
Origin: posterior surface of the middle third of the tibia.
Insertion: its tendon of insertion is formed behind the medial malleolus, positioned anterior to the tendon of the other intermediate muscle; and separated from the posterior n.v.s. The tendon proceeds to the sole of the foot where it divides into four tendons that are inserted to the distal phalanges of the four lateral toes.
Flexor hallucis longus
Origin: lateral fleshy muscle arising from the posterior surface of the middle of the fibula.
Insertion: its tendon is positioned posterior to that of the FDL, to continue at the sole of the foot where it courses near the medial border of the foot to reach its insertion at the distal phalanx of the hallux.
Popliteus – lies obliquely across the back of the knee, partly between the synovial membrane and the fibrous capsule of the joint.
Origin: the muscle fibers arise from the tendon attached to the popliteal sulcus (pit) at the lateral epicondyle, deep to the plantaris and lateral heal of the gastrocnemius.
Insertion: its fibers spread out towards their fleshy attachments at the soleal or oblique line at the back of the upper third of the tibia
Actions: helps in flexion and medial rotation of the leg
Tibialis Posterior – deepest muscle placed between the leg bones.
Origins: adjacent surfaces of the upper third of the tibia and fibula and the interosseous membrane.
Insertion: its fibers join a slender tendon which occupies the malleolar groove behind the medial malleolus, deep and anterior to the tendons of the intermediate muscles. The tendon continues to the sole of the foot where it spreads out to be attached to the tuberosity of the navicular, to the cuboid and to the bases of the 2,3, and 4 metatarsals.
Action: primarily an invertor of the foot, but it also helps in its adduction and plantar flexion
Neuro-vascular Structures in the Posterior Compartment of the Leg
Posterior Tibial Artery
Commencement: inferior border of the popliteus muscle.
It descends vertically between the intermediate muscles behind the posterior tibialis muscle.
Behind the medial malleolus it lies between the FDL in front and the FHL behind.
As it emerges below the inferior border of the flexor retinaculum, it divides into terminal “medial and lateral plantar arteries” which are distributed to the tissues of the sole of the foot.
1. Peroneal artery – largest branch given off laterally near the commencement of the parent trunk. It lies deep to the FHL, descending vertically to the ankle, where it gives off terminal “calcanean and malleolar branches” and a “perforating branch” that penetrates the interosseous membrane to reach the anterior compartment and descends to the dorsum of the foot where its last branches participate in the anastomoses around the ankle.
2. Posterior tibial recurrent – (may occasionally branch out from the anterior tibial artery). It participates in the anastomoses around the knee.
3. Circumflex fibular artery – (may also branch from the anterior tibial artery). It winds around the neck of the fibula to supply the lateral compartment of the leg.
4. Muscular and nutrient arteries to the bones.
The parent trunk passes behind the lateral malleolus to the lateral side of the foot where it ends by anastomosing with neighboring arteries.
5. Malleolar and calcanean branches – that anastomose with similar branches from the anterior tibial and peroneal arteries around the ankle joint, and with tarsal branches from those arteries.
Vena comites of these arteries unite to form veins that course with the posterior tibial artery to the popliteal region where they join with the anterior tibial veins to form the popliteal vein.
Superficial Group Muscle Origin Insertion Action Nerve Supply Gastrocnemius medial and lateral condyles of femur calcaneum plantar flexes (flexes) foot; flexes knee tibial nerve Plantaris lateral supracondylar ridge of femur calcaneum plantar flexes foot; flexes knee tibial nerve Soleus shafts of tibia and fibula calcaneum with gastrocnemius, a powerful plantar flexor of ankle; main propulsive force in walking and running tibial nerve
Deep Group Muscle Origin Insertion Action Nerve Supply Flexor digitorum longus shaft of tibia distal phalanges of lateral four toes flexes distal phalanges of lateral four toes; plantar flexes foot; supports lateral longitudinal arch of foot tibial nerve Flexor hallucis longus shaft of fibula base of distal phalanx of big toe flexes distal phalanx of big toe; plantar flexes foot; supports medial longitudinal arch of foot tibial nerve Tibialis posterior shafts of tibia and fibula and interosseous membrane tuberosity of navicular bone plantar flexes foot; inverts foot at subtalar and transverse tarsal joints; supports medial longitudinal arch of foot tibial nerve
The Plantar Region (Sole of the Foot)
Skin – thick, especially at the heel and beneath the heads of the metatarsals (termed metatarsal pad). It is adherent to the tough underlying fascia especially at the heel. In a live subject, observe that despite its thickness, the skin is discerningly sensitive as to differentiate objects felt at the sole of the foot, or to feel the pain caused by the penetration of a very tiny sliver of wood or any other sharp object.
Deep Fascia – strong, dense with a central shiny condensation called “plantar aponeurosis” which protects the deeper structures. It divides into 5 slips for the toes, which are reinforced by transverse fibers attached to the metatarsal ligaments of corresponding bones. Its posterior end is attached to the calcaneus. From its deep surface, fibrous septae separate the deeper layers of muscles and tendons.
Superficial First Layer
Composed of 2 abductors at the medial and lateral borders of the foot, and 1 flexor muscle in the middle of the sole.
Origin: Each muscle arises from the corresponding lateral and medial sides of the calcaneus.
Abductor Hallucis and Abductor Digiti Minimi Quinti
Insertion: base of the proximal phalanges of the corresponding digits.
(The tendon of the abductor hallucis is usually provided with a small sesamoid bone below the head of the first metatarsal bone).
Flexor Digitorum Brevis
Insertion: divides into 4 tendons, one for each of the four lateral toes. Each of those small tendons splits to be attached to the sides of the middle phalanx of the corresponding digit.
Second Layer 2 muscles and 2 tendons
Flexor Accessorius (or Quadratus Plantae)
Origin: two heads from the lateral and medial sides of the calcaneus.
Insertion: tendon of the Flexor digitorum longus, thus helping its action.
Origin: 4 small muscular slips each of which arise from a tendon of the FDL.
Insertion: each of the 4 small tendons joins the dorsally located extensor tendon of the corresponding digit.
Tendon of the Flexor Digitorum Longus – from the medial border of the foot it proceeds forwards beneath (superior to) the belly of the flexor digitorum brevis; dividing into 4 tendons, each of which passes between the split tendons of insertion of the brevis towards its insertion at the tip of the distal phalanx of the corresponding digit.
Tendon of the Flexor Hallucis Longus – courses deep to the abductor hallucis at the medial border of the foot towards its insertion at the tip of the distal phalanx of the big toe.
Third layer 2 flexors and one adductor
Flexor hallucis brevis
Origin: lateral cuneiform and cuboid bones.
Insertion: sides of the base of the proximal phalanx of the first digit.
Flexor digiti minimi
Origin: base of the 5th metatarsal
Insertion: base of the proximal phalanx of the 5 th toe.
Adductor hallucis – has two heads of origin:
Origin: oblique head – bases of the 2nd , 3rd, and 4th metatarsals.
Insertion: base of the first phalanx of the big toe at the middle of the sole.
transverse head – deep metatarsal ligaments, close to the heads of the 3rd –5th metatarsal bones.
Insertion: lateral side of the base of the first phalanx of the 1 st digit .
Fourth layer 2 tendons and 2 sets of muscles
Tendon of the Peroneus Longus – enters at the lateral border of the sole, extending obliquely forwards and medially to its insertions at the medial cuneiform and base of the first metatarsal bone.
Tendon of the Tibialis Posterior – winds around the medial border of the foot towards its insertions at the navicular, cuneiforms and cuboid, and the bases of the metatarsals.
3 Plantar and 4 Dorsal Interosseous Muscles – located close to each other in the inter-metatarsal space. Generally, they arise from the adjacent sides of the metatarsal bones. Each of their slender tendons insert at the sides of the bases of the proximal phalanges of the 3 lateral toes.
The plantar interossei adduct the digits while the dorsal interossei abduct them. NS: lateral plantar nerve
Muscle Origin Insertion Action Nerve Supply First Layer Abductor hallucis medial tubercle of calcaneum medial side, base proximal phalanx big toe flexes, abducts big toe. Supports medial longitudinal arch medial plantar Flexor digitorum brevis medial tubercle of calcaneum middle phalanx of four lateral toes flexes lateral four toes. Supports medial and lateral longitudinal arches medial plantar Abductor digiti minimi medial and lateral tubercles of calcaneum lateral side base proximal phalanx fifth toe flexes, abducts fifth toe. Supports lateral longitudinal arch lateral plantar
Second Layer accessory flexor (quadratus plantae) medial and lateral sides of calcaneum tendon flexor digitorum longus aids long flexor tendon to flex lateral four toes lateral plantar nerve lumbricals tendons of flexor digitorum longus dorsal extensor expansion of lateral four toes extends toes at interphalangeal joints first lumbrical-medial plantar; remainder-deep branch lateral plantar
Third Layer Flexor hallucis brevis cuboid, lateral cuneiform; tibialis posterior insertion medial and lateral sides of base of proximal phalanx of big toe flexes metatarso-phalangeal joint of big toe; supports medial longitudinal arch Medial plantar Adductor hallucis, oblique head bases second, third, fourth metatarsal bones lateral side base proximal phalanx big toe adducts big toe, supports transverse arch deep branch lateral plantar Adductor hallucis, transverse head capsules 3, 4, 5 metatarsophalangeal joints lateral side of base of proximal phalanx, big toe adduct big toe deep branch lateral plantar Flexor digiti minimi brevis base of 5th metatarsal lateral side base of proximal phalanx 5th toe flexes little toe lateral plantar
Fourth Layer Dorsal interossei (4) adjacent sides of metatarsals bases of phalanges and dorsal expansion of corresponding toes abduct toes, using second toe as reference flex metatarsophalangeal joints; extend interphalangeal joints Lateral plantar Plantar interossei (3) 3rd, 4th, 5th metatarsals bases phalanges and dorsal expansion 3rd, 4th, 5th toes adduct toes using second toe as reference flex metatarso-phalangeal joints; extend interphalangeal joints Lateral plantar
Neurovascular Structures at the Sole of the Foot
These structures enter the sole at the medial border of the foot. Their course is mostly between the first and second layers, the nerves being at the inner side of the vessels.
Medial Plantar Vessels – accompanied by a larger medial plantar nerve. These structures course directly forwards, covered by the abductor hallucis. The nerve innervates the abductor and flexor hallucis brevis, flexor digitorum brevis and the first lumbrical muscles.
Lateral Plantar Vessels – larger, and the accompanying nerve is smaller. They cross the middle of the sole to the lateral toes. At the level of the head of the metatarsals, the artery recurves towards the medial side as a “plantar arch”, giving digital branches. The nerve innervates the small muscles of the 5th digit including the flexor accessorius, adductor hallucis and 3 lateral lumbricals and all the interosseous muscles.
The veins join to form the posterior tibial vein at the flexor retinaculum.