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Proximal phalanx of great toe

The proximal phalanx of the great toe (hallux) is the first bone of the great toe, articulating proximally with the first metatarsal and distally with the distal phalanx. It serves as the main structural component of the first metatarsophalangeal (MTP) joint, which is critical for propulsion, balance, and weight transfer during gait.

It is a short tubular bone with a well-developed base, shaft, and head. The bone transmits forces generated by the flexor and extensor muscles of the great toe and provides attachment sites for multiple tendons and ligaments that stabilize the MTP joint. The bone marrow is bright on both T1 and T2 sequences due to the presence of fatty marrow, especially in adults.

Synonyms

  • First phalanx of the hallux

  • Proximal phalanx of the first toe

Location and Description

The proximal phalanx lies between the first metatarsal and the distal phalanx, forming the first interphalangeal unit of the foot. It is the largest phalanx of all the toes, reflecting the hallux’s critical role in push-off during locomotion.

The bone consists of:

  • Base (proximal end): Broad and concave, articulates with the head of the first metatarsal at the MTP joint

  • Shaft (body): Cylindrical and slightly flattened, providing attachment for fibrous sheaths of flexor and extensor tendons

  • Head (distal end): Convex articular surface articulating with the base of the distal phalanx

Relations

  • Proximally: Articulates with the head of the first metatarsal (MTP joint)

  • Distally: Articulates with the distal phalanx of the great toe (interphalangeal joint)

  • Dorsally: Related to tendons of extensor hallucis longus and extensor hallucis brevis

  • Plantar surface: Related to flexor hallucis longus and flexor hallucis brevis tendons

  • Medially/Laterally: Stabilized by medial and lateral collateral ligaments and sesamoids

Ossification

  • Primary ossification center: Appears in the shaft around 8–10 weeks of fetal life

  • Secondary ossification center: Appears at the base around age 3–4 years and fuses during adolescence

  • Marrow: Converts from red to fatty marrow with maturation (appears bright on both T1 and T2 MRI)

Attachments

  • Dorsal surface: Extensor hallucis longus and extensor hallucis brevis tendons

  • Plantar surface: Insertion of flexor hallucis brevis via medial and lateral tendons

  • Sides: Collateral ligaments of the first MTP and interphalangeal joints

Arterial Supply

  • Dorsal metatarsal arteries (branches of dorsalis pedis artery)

  • Plantar digital arteries (from medial plantar artery)

Venous Drainage

  • Dorsal digital veins → dorsal venous arch

  • Plantar digital veins → medial plantar venous plexus

Nerve Supply

  • Medial plantar digital nerve (branch of medial plantar nerve)

  • Proper plantar digital branch of deep peroneal nerve (dorsal aspect)

Function

  • Weight transmission: Transfers load from the first metatarsal to the distal phalanx

  • Joint movement: Enables flexion and extension of the great toe at the MTP and IP joints

  • Balance and propulsion: Essential for push-off during walking and running

  • Tendon leverage: Acts as a fulcrum for flexor and extensor tendons, enhancing mechanical efficiency

Clinical Significance

  • Fractures: Common from direct trauma or repetitive stress; may be intra-articular or avulsion type

  • Osteoarthritis: Degenerative changes of MTP joint may involve proximal phalanx articular base

  • Sesamoiditis and bunion deformities: Alter joint alignment and stress distribution

  • Bone marrow edema: Seen in trauma, infection, or inflammatory arthritis

  • Imaging role: MRI detects marrow, cortical, and soft-tissue changes better than radiographs

MRI Appearance

  • T1-weighted images:

    • Bone cortex: low signal (dark)

    • Bone marrow: bright due to fatty marrow

    • Corticomedullary differentiation: distinct

    • Pathology (fracture, marrow edema): focal low signal replacing normal bright marrow

  • T2-weighted images:

    • Bone cortex: low signal (dark)

    • Bone marrow: bright, reflecting fatty content (slightly less intense than subcutaneous fat)

    • Marrow edema or contusion: hyperintense regions replacing normal bright pattern

    • Joint effusion: high signal in MTP or IP joints

  • STIR:

    • Normal marrow: intermediate to dark signal (fat suppression reduces brightness)

    • Marrow edema, osteomyelitis, or fracture: bright hyperintense signal replacing normal marrow pattern

  • Proton Density Fat-Saturated (PD FS):

    • Cortex: dark

    • Normal marrow: intermediate-to-dark due to fat suppression

    • Abnormal marrow: focal or diffuse bright hyperintense areas in bone trauma or infection

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: mild uniform enhancement

    • Pathologic bone: strong enhancement in infection, inflammation, or tumor

    • Post-traumatic reactive enhancement at fracture margins

CT Appearance

Non-Contrast CT:

  • Bone: well visualized with dense cortical margins and trabecular pattern

  • Fractures: clearly delineated as cortical discontinuities or lucencies

  • Degenerative changes: joint space narrowing, osteophytes, subchondral sclerosis

  • Sesamoid relationships and plantar surface anatomy easily assessed

Post-Contrast CT (standard):

  • Bone itself does not enhance

  • Adjacent soft-tissue or periosteal inflammation may enhance

  • Useful for detecting subtle cortical irregularities, erosions, or early osteomyelitis

MRI image

Proximal phalanx of great toe foot coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Proximal phalanx of great toe foot sagittal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Proximal phalanx of great toe CT sagittal image

MRI image

distal phalanx foot SAG cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000