Anatomy, Bony Pelvis and Lower Limb, Foot Muscles

Structure and Function

Foot Compartments

The foot muscles are organized into 9 compartments enclosed by fascia. However, previous studies on the exact delineation of these compartments have varied considerably.[1][2]

The medial compartment contains the abductor hallucis, flexor hallucis brevis, and the tendon of the flexor hallucis longus. The lateral compartment contains the abductor digiti minimi and flexor digiti minimi. The superficial central compartment includes the flexor digitorum brevis, the 4 lumbricals, and the tendons of the flexor digitorum longus. The deep central (calcaneal) compartment, which communicates with the deep posterior compartment of the lower leg, contains the quadratus plantae and the posterior tibial neurovascular bundle. The adductor compartment contains the adductor hallucis.

Four interosseous compartments exist. The 1st lies between the 1st and 2nd metatarsals and contains the 1st dorsal interosseous muscle. The 2nd lies between the 2nd and 3rd metatarsals and contains both the dorsal and plantar interosseous muscles. The 3rd and 4th lie between the 3rd and 4th, and 4th and 5th metatarsals, respectively, and also contain the dorsal and plantar interosseous muscles.[3][4][5][6]

Foot musculature may also be categorized as extrinsic, originating outside the foot, or intrinsic, originating within the foot.[7][8][9] The intrinsic muscles are further divided into dorsal and plantar groups, with the plantar muscles arranged in 4 distinct layers.

Extrinsic Muscles of the Foot

Extrinsic foot muscles arise from the tibia, fibula, and surrounding structures of the lower leg, extending distally to act on the foot (see Image. Tendons of the Extrinsic Foot Muscles). These muscles enable plantarflexion, dorsiflexion, inversion, and eversion, thereby supporting weight-bearing and dynamic postural adjustments. Table 1 summarizes the origins, insertions, actions, blood supply, and innervation of the major extrinsic muscles of the foot (see Table 1. Overview of the Extrinsic Foot Muscles).

Table 1. Overview of the Extrinsic Foot Muscles

From the lateral leg compartment

The lateral compartment of the leg encases the fibularis longus and fibularis brevis muscles. Both are primarily involved in foot eversion and plantarflexion.

The fibularis longus originates from the head and proximal 1/2 of the fibula. The muscle's tendon passes posterior to the lateral malleolus and inserts onto the posterolateral aspect of the medial cuneiform and the lateral surface of the base of the 1st metatarsal. In addition to contributing to eversion and plantarflexion, the fibularis longus reinforces the transverse arch of the foot. The muscle receives vascular supply mainly from branches of the anterior tibial artery and is innervated by the superficial fibular nerve.

The fibularis brevis arises from the distal 2/3 of the fibula’s lateral surface and attaches to the styloid process of the 5th metatarsal. The muscle assists the fibularis longus in foot eversion and plantarflexion. The fibular artery provides the principal blood supply, and the superficial fibular nerve supplies motor innervation.

From the anterior leg compartment

The anterior compartment of the leg comprises the fibularis tertius, tibialis anterior, extensor hallucis longus, and extensor digitorum longus muscles. Collectively, these muscles facilitate dorsiflexion of the foot, with additional roles in toe extension, inversion, eversion, and abduction.

The fibularis tertius originates from the inferior 1/3 of the middle fibular shaft and the interosseous membrane. Insertion occurs on the dorsal surface of the 5th metatarsal. The muscle contributes to dorsiflexion, eversion, and abduction of the foot. Vascular supply is derived from the anterior tibial artery, and innervation arises from the deep fibular nerve.

The tibialis anterior emerges from the lateral condyle and proximal 1/2 of the tibial shaft, the superomedial surface of the fibula, and the interosseous membrane. The tendon inserts onto the medial and plantar segments of the medial cuneiform and the base of the 1st metatarsal. The muscle produces dorsiflexion and inversion of the foot. The anterior tibial artery provides blood supply, and the deep fibular nerve provides motor innervation.

The extensor hallucis longus emanates from the middle anterior margin of the fibula and the interosseous membrane and inserts on the dorsal portion of the distal phalanx of the great toe. The muscle extends the great toe and assists in dorsiflexion of the foot. The anterior tibial artery perfuses the muscle. The deep fibular nerve provides motor fibers.

The extensor digitorum longus originates from the lateral tibial condyle, the superomedial surface of the fibula, and the interosseous membrane. Insertion occurs on the dorsal surfaces of the distal and middle phalanges of the lateral 4 toes. The muscle extends the lateral 4 toes and aids foot dorsiflexion. The anterior tibial artery provides circulation. The deep fibular nerve supplies motor input.

From the superficial posterior leg compartment 

The superficial posterior leg compartment houses the gastrocnemius and soleus muscles. Both are primarily responsible for plantarflexion of the foot.

The gastrocnemius extends from the medial and lateral femoral condyles. The muscle's tendon merges with that of the soleus, forming the Achilles tendon, which inserts onto the calcaneus. The sural branch of the popliteal artery perfuses the gastrocnemius. Motor innervation is via the tibial nerve.

The soleus arises from the upper 1/4 of the posterior fibula and the middle posterior surface of the tibia. The tendon of this muscle fuses with the gastrocnemius tendon to form the Achilles tendon, which inserts on the calcaneus. Perfusion is supplied by the posterior tibial, fibular, and sural arteries, while the tibial nerve provides motor input.

From the deep posterior leg compartment

The deep posterior leg compartment contains the tibialis posterior, as well as the flexor hallucis longus and flexor digitorum longus. Collectively, these muscles contribute to plantarflexion, inversion, adduction, toe flexion, and support of foot supination.

The tibialis posterior originates from the superior 2/3 of the medial posterior tibia, the posterior fibula, and the interosseous membrane. The muscle's superficial tendon inserts on the navicular tuberosity, cuneiforms, and cuboid, while its deep tendon attaches to the plantar surfaces of the 2nd to 4th metatarsals. The tibialis posterior performs inversion, adduction, and plantarflexion, aiding foot supination. The sural, fibular, and posterior tibial arteries supply circulation. The tibial nerve provides motor input.

The flexor hallucis longus arises from the inferior 2/3 of the posterior fibula and the inferior aspect of the interosseous membrane. This muscle inserts on the plantar surface of the distal phalanx of the 1st digit, flexing the digit and contributing minimally to supination and plantarflexion. Perfusion is derived from the fibular and posterior tibial arteries. The tibial nerve supplies motor fibers.

The flexor digitorum longus originates from the posterior tibia distal to the soleal line and inserts on the plantar margins of the distal phalanges of digits 2 to 5. The muscle flexes these digits and may assist in plantarflexion. Perfusion emanates from the posterior tibial artery, with motor innervation from the tibial nerve.

Dorsal Intrinsic Muscles of the Foot

Intrinsic muscles on the dorsal surface of the foot originate and insert within the foot itself. These muscles are confined to the dorsal aspect of the foot and act locally on the toes. The dorsal intrinsic muscles facilitate extension of the digits and contribute to stabilization of the forefoot and the metatarsophalangeal (MTP) joints during weight-bearing activities (see Image. Muscles of the Anterior Leg Compartment and the Foot Dorsum). Table 2 outlines the key anatomical features and actions of the dorsal intrinsic muscles of the foot (see Table 2. Overview of the Dorsal Intrinsic Foot Muscles).

Table 2. Overview of the Dorsal Intrinsic Foot Muscles

Extensor digitorum brevis

The extensor digitorum brevis extends from the dorsolateral surface of the calcaneus, the inferior extensor retinaculum, and the talocalcaneal interosseous ligament. The muscle's tendon attaches to the extensor expansions of the extensor digitorum longus tendons for toes 2 to 4, facilitating extension of the lateral 3 digits. The fibular, anterior tibial, and dorsalis pedis arteries perfuse the muscle. The deep fibular nerve supplies motor innervation.

Dorsal interossei

The 4 dorsal interossei arise from the adjacent sides of metatarsals 1 to 5. These muscles insert onto the bases of the proximal phalanges and extensor expansions of toes 2 to 4 (see Image. Dorsal Interossei of the Foot). The dorsal interossei abduct toes 2 to 4 at the MTP joints and assist in both flexion and extension. The dorsalis pedis, plantar metatarsal, and lateral plantar arteries supply the muscle. Motor input comes from the lateral plantar nerve.

Extensor hallucis brevis

The extensor hallucis brevis originates from the dorsal surface of the calcaneus, superolateral to the origin of the extensor digitorum brevis. The muscle's tendon inserts onto the base of the proximal phalanx of the 1st digit, producing extension of the digit. Perfusion is via the dorsalis pedis artery. The deep fibular nerve innervates the muscle.

Plantar Intrinsic Muscles of the Foot

Muscles in this group are located on the foot sole and primarily function to support the arches and facilitate toe movements. The plantar intrinsic foot muscles are organized into 4 distinct layers based on their depth and anatomical relationships. Table 3 provides an overview of the 4 layers of plantar intrinsic foot muscles, including their structure, function, and neurovascular supply (see Table 3. Overview of the Plantar Intrinsic Foot Muscles).

Table 3. Overview of the Plantar Intrinsic Foot Muscles

First layer

The 1st layer of plantar muscles includes the abductor hallucis, flexor digitorum brevis, and abductor digiti minimi. These muscles contribute to toe abduction and flexion (see Image. Plantar Foot Anatomy, First Layer).

The abductor hallucis arises from the calcaneal tuberosity, the flexor retinaculum, and the plantar aponeurosis. The muscle's tendon inserts on the base and proximal phalanx of the great toe, producing abduction of the digit. The medial plantar artery supplies circulation, and the medial plantar nerve provides motor input.

The flexor digitorum brevis originates from the calcaneal tuberosity, plantar aponeurosis, and intermuscular septa. The muscle inserts onto the middle phalanges of digits 2 to 5, enabling flexion of these toes. The medial plantar artery provides circulation, and motor innervation comes from the medial plantar nerve.

The abductor digiti minimi arises from the calcaneal tuberosity, plantar aponeurosis, and intermuscular septa. This muscle's tendon attaches to the base of the 5th metatarsal, producing abduction of the 5th digit. Perfusion is supplied by the lateral plantar artery, with motor input from the lateral plantar nerve.

Second layer

The 2nd layer of plantar muscles comprises the quadratus plantae and the 4 lumbricals. These muscles aid in toe flexion and coordinated motion of the MTP and interphalangeal joints (see Image. Plantar Foot Anatomy, Second Layer).

The quadratus plantae originates from the plantar surface of the calcaneus and inserts onto the tendon of the flexor digitorum longus, assisting in flexion of the distal phalanges. Perfusion is supplied by the lateral plantar artery, and motor input is provided by the lateral plantar nerve.

The lumbricals extend from the tendons of the flexor digitorum longus and attach to the medial aspects of the extensor expansions on the proximal phalanges of digits 2 to 5. These muscles flex the MTP joints while extending the interphalangeal joints of toes 2 through 5. Perfusion is supplied by the medial and lateral plantar arteries. Motor innervation is provided by the medial plantar nerve for the 1st lumbrical and the lateral plantar nerve for the 2nd through 4th lumbricals.

Third layer

The 3rd layer of plantar muscles comprises the flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis. This group contributes to toe flexion and adduction (see Image. Plantar Foot Anatomy, Third Layer).

The flexor hallucis brevis originates from the cuboid and lateral cuneiform. The muscle's dual tendons insert onto the proximal phalanx of the great toe, producing flexion of the digit. The medial plantar artery supplies the flexor hallucis brevis. The medial plantar nerve provides motor input.

The adductor hallucis consists of an oblique head, arising from the bases of metatarsals 2 to 4, and a transverse head, originating from the MTP ligaments of digits 3 to 5. Both heads insert on the proximal phalanx of the great toe, facilitating adduction of the digit. Perfusion is provided by the 1st plantar metatarsal artery, with motor innervation supplied by the deep branch of the lateral plantar nerve.

The flexor digiti minimi brevis arises from the base of the 5th metatarsal and inserts onto the proximal phalanx of the 5th digit, producing flexion. The lateral plantar artery supplies perfusion, and the lateral plantar nerve provides motor input.

Fourth layer

Situated within the foot’s 4th muscular layer, the 3 plantar interossei muscles originate from the medial sides of metatarsals 3 to 5 and insert onto the proximal phalanges of the corresponding digits (see Image. Plantar Interossei of the Foot). These muscles adduct and flex toes 3 to 5 and assist the lumbricals in extending the interphalangeal joints. The plantar metatarsal artery supplies circulation. The lateral plantar nerve provides motor fibers.

Embryology

Limb development begins during the 4th postovulatory week, corresponding to embryonic stage 13 (3-6 mm in length).[10] Limb formation progresses in a proximodistal direction, with the foot appearing at approximately 4.5 weeks (embryonic stage 15). The cartilaginous skeleton and associated musculature become visible within days, followed shortly by the appearance of the digits (embryonic stage 18-19). Skeletal elements initially form as mesodermal condensations, which subsequently organize in a defined sequence. Ossification proceeds via the formation of a periosteal collar in tubular bones. Vascularization of the tarsal bones occurs during the fetal period, whereas endochondral ossification in certain tarsal bones does not commence until after birth.

The limbs originate from the proliferation of the somatopleuric mesoderm in the lateral body wall. These outgrowths form at the lumbar region corresponding to the 3rd through 5th lumbar somites for the hind limbs.[11]

Blood Supply and Lymphatics

The primary arterial supply to the foot originates from the popliteal artery, which is a continuation of the superficial femoral artery. The popliteal artery gives rise to 3 principal branches supplying the lower leg and foot, arranged from proximal to distal as the anterior tibial, fibular, and posterior tibial arteries (see Image. Arteries of the Lower Limb, Anterior and Posterior Views). The anterior tibial artery courses distally to supply the anterior and dorsal regions of the foot. After passing beneath the extensor retinaculum, this blood vessel continues as the dorsalis pedis artery, which is commonly palpated for the pedal pulse. The dorsalis pedis courses under the extensor hallucis longus and lies between this muscle and the extensor digitorum longus.

The dorsalis pedis gives rise to 3 lateral branches—the proximal tarsal, distal tarsal, and arcuate arteries—and 2 medial branches, the medial tarsal arteries. The arcuate artery originates at the level of the 1st tarsal-metatarsal joint and courses over metatarsals 2 to 4, giving rise to the 2nd, 3rd, and 4th dorsal metatarsal arteries. The 1st dorsal metatarsal artery arises directly from the dorsalis pedis. These metatarsal branches perfuse the dorsal interosseous muscles. The fibular artery supplies the lateral leg musculature and the posterior aspect of the foot. The posterior tibial artery provides circulation to the posterior and lateral leg as well as the plantar surface of the foot.

The posterior tibial artery bifurcates deep to the abductor hallucis into medial and lateral plantar branches. The medial plantar artery supplies the medial plantar surface and the hallux, whereas the larger lateral plantar artery traverses the sole to form the plantar arterial arch by uniting with the deep plantar branch of the dorsalis pedis artery. The arch gives rise to the plantar metatarsal arteries, which continue distally as the proper digital arteries to the toes (see Image. Plantar Foot Anatomy, Arterial Supply).

The lower limb's venous system consists of deep veins, which run between the muscles, and superficial veins, forming an intricate network immediately beneath the skin. These 2 systems are interconnected by valved transfascial vessels, the perforating veins, which direct approximately 10% of superficial blood flow into the deep venous system.

In the plantar region, a network of intertwined superficial and deep veins functions as a compressible reservoir, which is emptied with each step during ground contact. This mechanism facilitates the propulsion of blood from the foot toward the calf.

Venous return originates in the microcirculation, where arterial capillaries transition to venous capillaries. These blood vessels converge into collecting venules and, subsequently, into collecting veins, forming the initial efferent pathway of the macrocirculatory venous system.

In the anterior region, the dorsal venous network of the foot communicates through intercapitular veins that traverse the interdigital spaces. Digital veins, converging in pairs within the interdigital spaces, give rise to the metatarsal veins, which course into the deep plantar venous arch and subsequently converge in the lateral plantar veins. After posterior convergence with the medial plantar veins, the lateral plantar veins form the 2 posterior tibial veins. The anterior tibial veins originate from the deep veins of the dorsal foot. The medial marginal vein, rising anterior to the medial malleolus, empties into the great saphenous vein, whereas the lateral marginal vein, coursing anterior to the lateral malleolus, drains toward the small saphenous vein.

Lymphatic drainage of the lower extremities originates in the foot, where lymph nodes are classified as superficial (epifascial) or deep (subfascial). The epifascial and subfascial networks are interconnected by anastomoses. The epifascial system primarily drains the skin and subcutaneous tissues, while the subfascial system drains joints, muscles, and bones.[12] The major portion of epifascial collectors forms a ventromedial bundle over the dorsum of the foot, which empties into the superficial inguinal nodes, whereas a smaller dorsal bundle drains initially into the popliteal nodes.[13] The subfascial nodes drain into the deep inguinal nodes.

Nerves

The sciatic nerve constitutes the principal source of innervation for the lower extremity. This nerve emerges from the lumbosacral plexus and passes beneath the piriformis muscle before coursing distally. At the distal 1/3 of the femur, the sciatic nerve ramifies into the tibial and common fibular nerves. The tibial nerve descends distally, branching into the medial calcaneal, medial sural cutaneous, and medial and lateral plantar nerves (see Image. Plantar Foot Anatomy, Innervation). The common fibular nerve diverges into the superficial and deep fibular nerves. The superficial fibular nerve primarily provides cutaneous innervation to the dorsum of the foot, whereas the deep fibular nerve supplies motor fibers to the muscles responsible for foot dorsiflexion.[14][15]

Physiologic Variants

Tibialis Anterior Tendon

Variability exists in the insertion of the tibialis anterior tendon, which may give rise to potential alterations in force distribution across the foot and ankle. These differences become particularly relevant during tibialis anterior tendon ruptures, where restoration of tendon biomechanics may require alignment with the native insertion pattern.

Accessory Fibular Muscles

The fibularis quartus is an accessory muscle present in 6% to 22% of individuals, depending on the study. This muscle most commonly originates from the fibularis brevis, although origins from the fibularis tertius and longus have been reported. Insertion points vary, including the cuboid, lateral tubercle of the calcaneus, apophysis of the calcaneal cochlea, or the retrotrochlear eminence of the calcaneus. In some cases, the muscle gives rise to a tendon that inserts on the 5th digit, referred to as the "fibularis digiti quinti," which may assist in the extension of this digit.[16]

The presence of a fibularis quartus has been associated with lateral ankle pathology. Symptomatic individuals may present with chronic ankle pain in the absence of trauma. Additional reported pathologies include fibular tendon subluxation, tendinous calcification, and hypertrophy of the retrotrochlear eminence of the calcaneus, contributing to lateral hindfoot pain.[17]

Accessory Soleus Muscle

The accessory soleus muscle is an anatomical variant located anterior or anteromedial to the Achilles tendon, originating from the fibula, soleus, or tibia and inserting on the Achilles tendon or calcaneus. Prevalence ranges from 0.7% to 5.5% in the general population, though this variant is generally considered rare. An accessory soleus muscle may be asymptomatic or cause pain, swelling, exertional compartment syndrome, and neurovascular compression. Clinically, this variant can mimic soft-tissue tumors. Medical management involves activity modification, while surgical excision is indicated for persistent pain, functional limitation, or compartment syndrome, with careful dissection to prevent injury to surrounding tendons and neurovascular structures.[18][19]

Surgical Considerations

Foot Drop

Foot drop is a condition marked by weakness or paralysis of the muscles responsible for ankle dorsiflexion, often resulting in a steppage gait and functional impairment. In many cases, foot drop arises iatrogenically from surgical injury to the deep fibular nerve or its branches during procedures involving the foot, ankle, or distal leg. Surgical interventions, including neurolysis, nerve repair, and tendon transfers, are employed to restore motor function, depending on the severity and chronicity of nerve damage. Early identification and tailored operative management can significantly improve functional outcomes and reduce long-term disability.[20]

Foot Reconstruction Using Muscle Flaps

Foot muscle flap surgeries use vascularized muscle tissue to reconstruct soft-tissue defects over bone, tendon, or joint exposures. Examples include the abductor hallucis muscle flap, typically used for medial-column or 1st MTP joint defects, and the flexor hallucis brevis muscle flap, applied to cover forefoot soft tissue injuries.[21][22] Intrinsic muscle flaps are suitable for smaller defects, often combined with split-thickness skin grafts to enhance healing. Indications include chronic ulcers, osteomyelitis, and trauma.[23] Microsurgical free muscle transfers are employed for extensive defects when local flaps are insufficient, allowing vascularized tissue coverage and functional restoration.[24]

Risks of Dorsalis Pedis Artery Anomalies

Variations in the origin, course, and branching of the dorsalis pedis artery are observed in approximately 20% to 30% of examined feet, including absence, lateral deviation, duplication, or replacement by a branch of the fibular artery.[25] The plantar arterial arch shows variability in completeness and the dominant contributor. Cadaveric studies indicate that the plantar arterial arch is usually complete, with variable dominance of the lateral plantar artery or the deep plantar branch of the dorsalis pedis artery. In some cases, both vessels contribute roughly equally to the arch.[26]

Unrecognized variation may lead to unexpected ischemia, arterial disruption in dorsal-midfoot surgery, or flap reconstruction failure in the forefoot.[27] Preoperative imaging can help prevent intraoperative vascular complications.

Clinical Significance

Muscles acting directly on or surrounding the foot mediate multiple functions essential for normal gait and postural stability. Injury to these muscles can lead to conditions that impair the performance of activities of daily living. Common disorders associated with foot musculature include Achilles tendon rupture, hammer toe, and pes planus (flat foot), each presenting with variable functional impairment and potential comorbidities. Management strategies are determined by the severity of the condition and the patient's age. For instance, conservative nonoperative treatment of Achilles tendon rupture has demonstrated outcomes comparable to surgical intervention in older patients.[28]

Other Issues

Flexor Hallucis Longus Transfer for Achilles Rupture

Chronic Achilles tendon rupture includes cases where the rupture persists or is untreated for more than 4 weeks following the initial injury, resulting in tendon retraction, poor vascularization, and atrophic tendon ends. The condition often arises from missed acute injuries and is increasingly common in adults aged 30 to 40. Weak plantarflexion persists due to compensation by tibialis posterior, peroneus, flexor hallucis longus, and flexor digitorum longus, causing impaired gait and push-off strength.

Surgical management via single-incision flexor hallucis longus tendon transfer addresses large tendon defects (>5 cm), restoring ankle function and daily activity. Benefits include low rerupture rates and significant functional improvement. Risks involve hallux plantarflexion weakness, wound complications, and rare nerve injury. Long-term follow-up demonstrates high patient satisfaction and durable correction in the majority of cases.[29]

Overuse Injuries from Ballet Training

Recurrent plantarflexion, forefoot elevation (relevé), and sustained distal toe loading (en pointe) contribute to foot and ankle overuse injuries in ballet dancers. Common conditions include Achilles tendinopathy, plantar fasciitis, metatarsal stress fractures, hallux valgus, and claw or hammer toes. Movements that require extreme dorsiflexion and toe extension overload the intrinsic foot muscles, flexor hallucis longus, gastrocnemius-soleus complex, and tibialis posterior. Repeated en pointe activity particularly stresses the medial longitudinal arch and 1st MTP joint. Preventive strategies include targeted strengthening, gradual load progression, proper technique, and structured rest.[30]