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Hook of hamate bone

The hook of the hamate (hamulus) is a prominent curved bony projection on the palmar surface of the hamate bone, one of the distal carpal bones of the wrist. It is located on the ulnar side of the distal carpal row, forming part of the medial border of the carpal tunnel and the lateral wall of Guyon’s canal.

This hook-shaped process serves as a critical attachment point for ligaments and tendons, including the transverse carpal ligament, pisohamate ligament, and the flexor carpi ulnaris tendon sheath. It protects the ulnar nerve and artery, which pass just medial to it through Guyon’s canal. Fractures of the hook are relatively common in golfers, racquet players, and baseball batters due to direct impact or repetitive stress.

Synonyms

  • Hamulus of the hamate

  • Hamular process

  • Hook process of the hamate

Location and Structure

  • The hamate bone lies on the ulnar side of the distal carpal row, articulating with the fourth and fifth metacarpal bases, the capitate, triquetrum, and lunate.

  • The hook (hamulus) projects palmarward and slightly laterally from the body of the hamate.

  • It is curved and flattened, forming a palpable bony prominence on the medial aspect of the wrist.

  • The hook provides a mechanical pulley for flexor tendons of the little and ring fingers.

Relations

  • Anteriorly (superficial): Palmar fascia and skin

  • Posteriorly (deep): Body of the hamate and carpometacarpal articulations

  • Medially: Pisiform bone and pisohamate ligament

  • Laterally: Carpal tunnel and transverse carpal ligament

  • Superiorly: Continuity with the body of the hamate

  • Inferiorly: Bases of the fourth and fifth metacarpals

  • Neurovascular relations: Ulnar nerve and artery pass medial and superficial to the hook within Guyon’s canal

Attachments

  • Ligaments:

    • Transverse carpal ligament: attaches laterally, forming part of the carpal tunnel roof

    • Pisohamate ligament: extends from pisiform to the hook, forming the floor of Guyon’s canal

    • Flexor retinaculum: partially attaches at the hook

  • Muscle attachments:

    • Flexor digiti minimi brevis: originates from the hook

    • Opponens digiti minimi: also arises from the hook

  • Tendinous relations:

    • Flexor digitorum profundus and superficialis tendons pass lateral to it

    • Ulnar nerve and artery lie just medial and superficial

Function

  • Structural support: Forms the ulnar boundary of the carpal tunnel and the radial wall of Guyon’s canal

  • Protection: Shields the ulnar nerve and artery from external compression

  • Attachment site: Provides origin for hypothenar muscles and ligaments

  • Mechanical pulley: Alters the direction of the flexor tendons of the ulnar digits for efficient finger flexion

  • Load distribution: Transmits forces between the hand and wrist during grip and push-off

Clinical Significance

  • Fracture: Common in sports such as golf, baseball, and racquet games due to direct impact from club or bat handle

  • Symptoms: Ulnar wrist pain, grip weakness, tenderness over hypothenar eminence, and possible ulnar nerve paresthesia

  • Complications: Nonunion due to poor vascular supply, ulnar nerve entrapment in Guyon’s canal, or chronic pain

  • Surgical relevance: Palpable landmark for decompression of Guyon’s canal and carpal tunnel release

  • Imaging importance: MRI and CT crucial for detecting occult fractures, nonunions, and ulnar nerve entrapment

MRI Appearance

  • T1-weighted images:

    • Cortex: Low signal (dark line)

    • Marrow: Bright due to fatty content

    • Fracture: Appears as linear low-signal line through hook or base with surrounding intermediate signal from edema

    • Adjacent soft tissues: Fat bright, helping to delineate bone margins

    • Chronic nonunion: Margins may appear smooth and sclerotic, with a low-signal gap

  • T2-weighted images:

    • Cortex: Low signal

    • Marrow: Bright, though slightly less than T1

    • Fracture or edema: Bright hyperintense signal along fracture line or within adjacent marrow

    • Tendon irritation or ulnar nerve inflammation: Hyperintense peritendinous or perineural signal in Guyon’s canal

  • STIR:

    • Normal bone: Intermediate-to-dark signal

    • Acute fracture or contusion: Bright hyperintense signal in marrow or adjacent soft tissues

    • Useful for detecting occult fractures and early stress injuries

  • Proton Density Fat-Saturated (PD FS):

    • Normal hook: Intermediate-to-dark marrow signal

    • Pathology: Bright linear hyperintensity for fractures, edema, or inflammatory change

    • Excellent for evaluating perihamate soft-tissue inflammation or partial tendon tear of hypothenar origin

  • T1 Fat-Sat Post-Contrast:

    • Normal bone: Mild homogeneous enhancement

    • Fracture or nonunion: Peripheral rim enhancement around fracture margins

    • Osteomyelitis or soft-tissue infection: Irregular enhancement with marrow and pericortical extension

    • Entrapment neuropathy: May show focal enhancement along ulnar nerve course in Guyon’s canal

CT Appearance

Non-Contrast CT:

  • Cortex: High attenuation, sharply defined hook contour

  • Marrow: Intermediate density

  • Fracture: Linear cortical break or fragmentation at the base of the hook, sometimes minimally displaced

  • Chronic nonunion: Rounded margins and sclerotic ends with persistent gap

  • 3D CT reconstructions: Excellent for surgical planning and detection of small hook fragments

  • Soft-tissue evaluation: May show secondary ulnar nerve or tendon impingement

CT VRT 3D image

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CT VRT 3D image

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MRI image

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MRI image

Hook of hamate bone axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI image

Hook of hamate bone coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

CT image

Hook of hamate bone ct axial image