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Tuberosity of distal phalanx

The tuberosity of the distal phalanx is the roughened terminal part of the distal phalanx of each finger (and thumb). It forms the bony support for the pulp and nail bed, providing attachment for the fibrous flexor tendon sheath, digital pulp tissue, and fibrous septa anchoring the skin of the fingertip.

This region is critical for grip strength, tactile function, and precision movements. The distal phalangeal tuberosity also serves as the insertion point of the flexor digitorum profundus (FDP) tendon in the fingers and the flexor pollicis longus (FPL) in the thumb. Because of its compact shape and rich vascularity, it is a common site of tuft fractures, osteitis, and crush injuries.

Synonyms

  • Tuft of distal phalanx

  • Digital tuberosity

  • Terminal phalangeal process

Location and Structure

  • Position: At the distal end of the distal phalanx, beneath the nail bed and fingertip pulp.

  • Shape: Expanded, roughened, and flattened distally with a slightly convex dorsal surface and grooved palmar aspect.

  • Composition: Dense cortical bone enclosing a small cancellous core with fatty marrow.

  • Surface features:

    • Palmar surface: Gives attachment to the flexor tendon and fibrous septa of the fingertip pad.

    • Dorsal surface: Supports the nail bed.

    • Margins: Rounded and continuous with the shaft of the distal phalanx.

Relations

  • Dorsally: Nail bed and nail plate.

  • Palmar aspect: Fibrous pulp tissue, septa, and flexor tendon insertion.

  • Laterally: Digital fibrous sheath and collateral ligaments of distal interphalangeal joint.

  • Proximally: Shaft and head of the distal phalanx.

  • Distally: Terminal digital pad and skin of the fingertip.

Attachments

  • Tendinous:

    • Flexor digitorum profundus (FDP): Inserts into the palmar base of the distal phalanx (fingers).

    • Flexor pollicis longus (FPL): Inserts into the palmar base of the distal phalanx (thumb).

  • Fibrous structures:

    • Fibrous septa and digital pulp fascia anchor to the tuberosity, securing the skin of the fingertip.

    • Terminal extensor expansion passes dorsally over the tuberosity, blending with periosteum.

  • Soft tissue: Fibroadipose pulp and sensory nerve endings overlie the tuberosity, giving tactile sensitivity.

Function

  • Tendon attachment: Serves as the bony anchor for FDP or FPL tendons, essential for fingertip flexion.

  • Tactile support: Provides rigidity beneath the pulp, enabling precise object manipulation.

  • Protection: Supports nail bed and distal soft tissues against trauma.

  • Load transfer: Distributes pressure during grip and fingertip contact.

Clinical Significance

  • Tuft fractures: Common in crush injuries or door-slam trauma; may involve nail bed laceration.

  • Avulsion injuries: FDP tendon rupture (“Jersey finger”) causes loss of distal interphalangeal flexion.

  • Osteomyelitis: Infection secondary to open fingertip trauma or nail bed injury.

  • Subungual exostosis: Bony outgrowth from the dorsal aspect of the tuberosity under the nail bed.

  • Amputation stump evaluation: Important in fingertip reconstruction and flap surgeries.

  • Imaging relevance: Crucial in assessing bone integrity, tendon insertions, and post-traumatic deformity.

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark)

    • Bone marrow: Bright due to fatty content in normal adult bone

    • Flexor tendon insertion: Low-signal band attaching to palmar surface

    • Nail bed: Thin intermediate signal dorsal to bone

    • Pathology: Fractures appear as low-signal lines; marrow edema as intermediate-to-bright areas

  • T2-weighted images:

    • Cortex: Dark (low signal)

    • Marrow: Bright, slightly less than on T1 but higher than adjacent muscle

    • Flexor tendon: Dark low-signal band continuous with FDP or FPL

    • Nail bed and pulp: Intermediate-to-bright soft-tissue signal

    • Pathology: Bone edema, osteitis, or fractures appear as hyperintense signals within the tuberosity

  • STIR:

    • Normal marrow: Intermediate-to-dark signal

    • Abnormal marrow: Bright hyperintensity in edema, contusion, or infection

    • Soft tissue: Bright signal in pulp inflammation or cellulitis

  • Proton Density Fat-Saturated (PD FS):

    • Normal bone marrow: Intermediate-to-dark signal

    • Abnormal marrow: Bright focal hyperintensity representing edema or early infection

    • Flexor tendon insertion: Low signal; tears or tendinopathy show localized bright areas

    • Ideal for evaluating small avulsion injuries and soft-tissue integrity

  • T1 Fat-Sat Post-Contrast:

    • Normal tuberosity: Homogeneous mild enhancement

    • Infection or osteomyelitis: Patchy marrow enhancement with cortical disruption

    • Soft-tissue abscess or granulation: Peripheral rim enhancement

    • Tendon inflammation: Linear enhancement at insertion site

CT Appearance

Non-Contrast CT:

  • Cortex: High-attenuation dense bone with smooth contour

  • Marrow cavity: Low-density core corresponding to fatty content

  • Tendon insertion: Seen as a fine groove or roughened palmar surface

  • Pathology:

    • Fractures: Linear lucencies or comminution at tuft region

    • Osteomyelitis: Cortical erosion and periosteal reaction

    • Subungual exostosis: Irregular bony outgrowth dorsally beneath nail bed

    • Chronic trauma: Sclerosis and contour irregularity

MRI images

Tuberosity of distal phalanx of hand axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000_00001

MRI images

Tuberosity of distal phalanx of hand coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT images

Tuberosity of distal phalanx ct coronal

CT images

Tuberosity of distal phalanx ct sagittal image

CT 3D VRT image

Tuberosity of distal phalanx of hand 3D VRT CT image -img-00000-00000