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Body of the phalanx (hand)

The body (shaft) of the phalanx is the elongated central portion of each phalangeal bone in the hand. It lies between the base (proximal end) and head (distal end) of the phalanx and forms the major portion of the bone’s structure. The phalanges make up the skeleton of the fingers — proximal, middle, and distal — with each (except the thumb) having a defined body that supports tendons and contributes to digital movement and dexterity.

The shaft is cylindrical and slightly concave on its palmar surface, allowing flexor tendons to lie closely against the bone, while the dorsal surface is flattened, providing attachment to the extensor tendon expansions. The phalangeal bodies are designed to resist bending forces while maintaining lightweight flexibility for precise finger motion.

Synonyms

  • Shaft of the phalanx

  • Phalangeal body

  • Central diaphysis of the phalanx

Location and Structure

  • Position: Between the base and head of each phalanx.

  • Shape: Cylindrical, tapering distally, with a gentle palmar concavity.

  • Composition: Outer cortical bone and inner trabecular (cancellous) bone enclosing the marrow cavity.

  • Surfaces:

    • Palmar surface: Concave, allowing accommodation of flexor tendons.

    • Dorsal surface: Flat, giving attachment to the extensor expansion.

    • Lateral surfaces: Smooth, providing attachment for fibrous sheaths and collateral ligaments.

  • Periosteum: Dense connective covering supplying blood vessels and facilitating fracture healing.

Relations

  • Anteriorly (palmar): Flexor digitorum profundus and flexor digitorum superficialis tendons, along with digital synovial sheaths.

  • Posteriorly (dorsal): Extensor expansions of extensor digitorum and lumbrical insertions.

  • Laterally: Collateral ligaments and fibrous digital sheaths.

  • Proximally: Base of the phalanx articulating with the preceding bone.

  • Distally: Head of the phalanx forming the interphalangeal joint.

Attachments

  • Dorsal surface: Attachment for the extensor expansion and interosseous aponeurosis.

  • Palmar surface: Covered by flexor tendons and vincula (vascular folds of tendon sheath).

  • Lateral borders: Connected to the fibrous digital sheaths and collateral ligaments.

Arterial Supply

  • Nutrient arteries derived from the digital branches of the proper palmar digital arteries (from superficial palmar arch).

  • Periosteal branches supply outer cortex.

Function

  • Structural support: Provides framework for tendons and interphalangeal joints.

  • Lever action: Acts as a rigid lever during flexion and extension of the fingers.

  • Attachment base: Serves as anchorage for tendinous and ligamentous structures.

  • Load transmission: Transmits compressive and tensile forces during grip and fine motor actions.

  • Dexterity: Contributes to stability, alignment, and precise finger control.

Clinical Significance

  • Fractures: Commonly occur from crush or torsional trauma; transverse or spiral patterns in middle and proximal phalanges.

  • Stress injury: Overuse or repetitive strain causes cortical thickening or microfractures.

  • Osteomyelitis: Infection secondary to trauma or bite injuries involving marrow cavity.

  • Tumors: Enchondromas, giant cell tumors, and metastases may affect phalangeal shafts.

  • Deformities: Malunion or shortening can affect hand function and tendon balance.

  • Imaging role: MRI and CT crucial for detecting subtle fractures, marrow edema, cortical breaches, or pathological lesions.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark, sharply marginated).

    • Marrow cavity: Bright signal (fatty marrow).

    • Periosteum: Thin low-signal rim.

    • Fracture lines: Appear as linear low-signal bands through bright marrow.

    • Soft-tissue plane: Surrounding fat bright, clearly delineating bone contour.

  • T2-weighted images:

    • Cortex: Dark, low signal.

    • Marrow: Bright signal, slightly less intense than T1.

    • Periosteal reaction or callus: Intermediate-to-bright signal in healing fractures.

    • Pathology: Edema or infection—bright hyperintense marrow replacing normal fatty signal.

  • STIR:

    • Normal marrow: Intermediate-to-dark signal intensity.

    • Pathology: Bright hyperintensity in areas of edema, infection, or tumor infiltration.

    • Excellent for early detection of marrow edema and stress fractures.

  • Proton Density Fat-Saturated (PD FS):

    • Normal bone marrow: Intermediate-to-dark, homogeneous signal.

    • Abnormal bone: Focal or diffuse bright hyperintensity representing inflammation or trauma.

    • Ideal for showing subtle cortical disruptions, periosteal reaction, or soft-tissue edema.

  • T1 Fat-Sat Post-Contrast:

    • Normal marrow: Mild homogeneous enhancement.

    • Infection or tumor: Patchy or ring-like enhancement.

    • Fracture repair: Peripheral or linear enhancement at callus site.

    • Osteomyelitis: Diffuse enhancement with cortical irregularity and adjacent soft-tissue enhancement.

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, sharply defined.

  • Trabecular bone: Fine reticular pattern within marrow cavity.

  • Fracture: Visible as cortical breaks or lucent lines; may reveal subtle nondisplaced fractures missed on X-ray.

  • Pathology:

    • Periosteal reaction, sclerosis, or cortical thinning in infection or neoplasm.

    • Expansile lesions (enchondroma, cyst) show internal septations and thinning of cortex.

  • Excellent for assessing fracture alignment, bone density, and cortical integrity.

MRI images

Body of the Phalanx of the Hand coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Body of the Phalanx of the Hand coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

CT image

Body of the Phalanx of the Hand coronal ct image

CT image

Body of the Phalanx of the Hand sag ct image