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Pisohamate ligament

The pisohamate ligament is a strong fibrous band of the wrist that extends from the pisiform bone to the hook of the hamate, forming part of the ulnar (Guyon’s) canal. It is a continuation of the tendon of the flexor carpi ulnaris (FCU) and plays a crucial role in protecting the ulnar nerve and artery as they pass through the canal into the hand.

This ligament contributes to the formation of both palmar and dorsal components of the ulnar tunnel, providing stabilization and compartmentalization of structures within the medial wrist. It forms the roof of Guyon’s canal when joined by the pisometacarpal ligament and palmar carpal ligament.

Synonyms

  • Pisohamate arch

  • Ligament of Guyon canal

  • Pisohamate band of the flexor carpi ulnaris

Origin, Course, and Insertion

  • Origin: From the distal and anterior aspect of the pisiform bone (which acts as a sesamoid bone within the flexor carpi ulnaris tendon).

  • Course: Fibers pass obliquely distolaterally and slightly dorsally toward the hook of the hamate, forming a fibrous bridge over the ulnar canal.

  • Insertion: Attaches to the hook of the hamate on its medial and palmar surface, merging with the pisometacarpal ligament and palmar fascia.

Dorsal and Palmar Aspects

  • Palmar surface: Forms part of the roof of Guyon’s canal, blending with palmar fascia and the palmar carpal ligament. It protects the superficial ulnar artery and nerve branches.

  • Dorsal surface: Lies adjacent to the deep portion of the ulnar canal, covering the deep branch of the ulnar nerve and vessels as they pass toward the hypothenar muscles.

Relations

  • Superiorly: Flexor carpi ulnaris tendon and palmar carpal ligament

  • Inferiorly: Roof of Guyon’s canal and hypothenar muscles (abductor digiti minimi)

  • Medially: Pisiform bone

  • Laterally: Hook of hamate and deep ulnar nerve branch

  • Posteriorly (dorsal side): Deep branch of ulnar nerve and artery passing into hypothenar region

  • Anteriorly (palmar side): Palmar carpal ligament and subcutaneous tissue

Function

  • Stabilization: Secures the pisiform to the hamate, maintaining integrity of the ulnar tunnel

  • Protection: Forms part of the fibrous roof of Guyon’s canal, shielding the ulnar neurovascular bundle

  • Force transmission: Transmits mechanical stress from the flexor carpi ulnaris tendon to the hamate during wrist flexion

  • Support: Contributes to the stability of the hypothenar eminence and medial carpal arch

  • Guidance: Provides a fibro-osseous tunnel for the deep branch of the ulnar nerve and vessels

Clinical Significance

  • Ulnar tunnel syndrome (Guyon’s canal syndrome): Compression of the ulnar nerve beneath the pisohamate ligament causing sensory and motor deficits in the hand

  • Trauma: Fractures or dislocations of the pisiform or hamate may strain or rupture the ligament

  • Accessory ossification: Calcification or ossified ligament may appear as a small bony density on imaging

  • Surgical importance: Serves as an anatomical landmark during decompression of the ulnar nerve

  • Tendinopathy and fibrosis: Chronic stress may lead to thickening, contributing to nerve entrapment or pain in the hypothenar region

MRI Appearance

  • T1-weighted images:

    • Ligament appears as a thin, low-signal (dark) linear band connecting the pisiform and hook of hamate.

    • Adjacent muscles (hypothenar) show intermediate signal; surrounding fat is bright, providing contrast.

    • Calcified or fibrotic ligament may appear as a focal signal void.

  • T2-weighted images:

    • Normal ligament: dark low-signal band; margins smooth and continuous.

    • Surrounding fat and fluid: bright hyperintense, outlining the ligament clearly.

    • Pathology (sprain or tear): focal hyperintense signal within ligament or discontinuity with periligamentous edema.

  • STIR:

    • Normal ligament: intermediate-to-dark signal.

    • Pathologic changes (edema, strain, partial tear): bright hyperintensity at pisiform or hamate attachment sites.

    • Useful for early detection of inflammatory or traumatic lesions.

  • Proton Density Fat-Saturated (PD FS):

    • Ligament: dark linear structure, sharply demarcated.

    • Partial tears: linear or spotty bright signal indicating fiber disruption.

    • Thickening and periligamentous edema appear as surrounding hyperintensity.

  • T1 Fat-Sat Post-Contrast:

    • Normal ligament: minimal or no enhancement.

    • Inflamed or fibrotic ligament: enhancing irregular margins.

    • Postoperative scarring or chronic entrapment: diffuse peripheral enhancement.

CT Appearance

Non-Contrast CT:

  • Ligament appears as a thin, soft-tissue density band connecting pisiform to hamate.

  • Best visualized on high-resolution coronal and axial planes.

  • Ossified or calcified portions: hyperdense foci along ligament course.

  • Associated fractures (pisiform or hamate): easily detected.

Post-Contrast CT (standard):

  • Enhances mildly along soft-tissue plane; inflammation or fibrosis shows greater enhancement.

  • Differentiates ligament thickening from small ganglion cysts or periligamentous soft-tissue swelling.

CT Arthrography Appearance

  • Contrast outlines Guyon’s canal and may delineate the pisohamate ligament as a thin low-density band separating contrast-filled spaces.

  • Ligament tears: contrast extends between pisiform and hamate, partially disrupting the continuity of the ligament line.

  • Chronic degeneration or scarring: irregular contour and poor contrast separation from adjacent tissues.

  • Useful for identifying ulnar nerve compression, fibrosis, or postoperative changes in Guyon’s canal.

MRI images

Pisohamate ligament axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Pisohamate ligament mri coronal image

MRI images

Pisohamate ligament mri sag image