Pisometacarpal Ligament: Anatomy, Function, Imaging

Topic

Pisometacarpal ligament

The pisometacarpal ligament (PML) is a fibrous band extending from the pisiform bone to the base of the fifth metacarpal on the ulnar side of the wrist. It is considered a distal continuation of the flexor carpi ulnaris (FCU) tendon and forms part of the ulnar carpal ligamentous complex, which also includes the pisohamate ligament.

The PML plays a critical role in transmitting FCU tension to the fifth metacarpal, thereby stabilizing the pisiform, hamate, and fifth carpometacarpal (CMC) joint. It consists of palmar (volar) and dorsal components that work synergistically to maintain ulnar wrist stability and fine-tune grip strength.

Synonyms

Pisiform–fifth metacarpal ligament
Ulnar carpometacarpal ligament (distal extension of FCU tendon)

Location and Structure

The pisometacarpal ligament originates from the pisiform bone, specifically its distal and ulnar aspects, and inserts into the base of the fifth metacarpal bone. It lies superficial to the pisohamate ligament, forming a key component of the ulnar carpal tunnel. The ligament fibers are short, strong, and oblique, blending with the palmar fascia and the tendon sheath of the FCU.

The palmar (volar) portion is thicker and bears more tension during wrist flexion, while the dorsal portion is thinner but contributes to rotational stability of the fifth metacarpal.

Dorsal and Palmar Parts

Palmar (volar) Pisometacarpal Ligament:
- Originates from the distal anterior surface of the pisiform.
- Blends with the flexor retinaculum and FCU tendon sheath.
- Inserts on the palmar base of the fifth metacarpal.
- Functionally stabilizes the fifth CMC joint during wrist flexion and grip.
Dorsal Pisometacarpal Ligament:
- Smaller and thinner than the palmar portion.
- Extends from the dorsal margin of the pisiform to the dorsal base of the fifth metacarpal.
- Provides resistance to excessive extension and ulnar deviation.

Relations

Anteriorly (palmar): Flexor carpi ulnaris tendon, palmar fascia, and hypothenar muscles
Posteriorly (dorsal): Extensor carpi ulnaris tendon and dorsal carpal ligaments
Medially: Pisohamate ligament and ulnar neurovascular bundle
Laterally: Base of fifth metacarpal and hamate
Deep: Fifth carpometacarpal joint capsule

Attachments

Proximal attachment: Distal aspect of pisiform bone (continuation of FCU tendon)
Distal attachment: Base and palmar ridge of fifth metacarpal
Associated structures: Merges with pisohamate ligament medially and ulnar carpal capsule laterally

Function

Joint stabilization: Maintains alignment and stability of the pisiform and fifth metacarpal during flexion and extension
Force transmission: Transfers tension from the FCU tendon to the fifth metacarpal and fifth CMC joint
Ulnar wrist integrity: Works with pisohamate and transverse carpal ligaments to stabilize the ulnar side of the wrist
Grip mechanics: Provides support during strong grasping and power grip motions
Dynamic role: Balances forces between flexor and extensor tendons during wrist movement

Clinical Significance

Pisiform instability: Rupture or attenuation of the ligament can cause pain and subluxation of the pisiform
Degenerative change: Chronic stress may lead to thickening, fibrosis, or ossification
Ulnar-sided wrist pain: May arise from enthesopathy or partial tear at its pisiform or metacarpal attachment
Surgical importance: Recognized landmark during FCU tendon harvest, pisiform excision, or ulnar tunnel decompression
Trauma: Avulsion injury may occur with hyperextension or impact to the ulnar wrist, sometimes accompanied by pisiform fracture

MRI Appearance

T1-weighted images:
- Ligament appears as a low-signal (dark) linear band extending between pisiform and base of fifth metacarpal
- Surrounding fat planes are bright, improving contrast
- Chronic thickening or fibrosis: intermediate signal
- Adjacent muscle and tendon margins clearly delineated
T2-weighted images:
- Normal ligament: low-signal intensity structure
- Partial tear or inflammation: focal hyperintense areas within or around the ligament
- Complete tear: discontinuity with fluid-filled gap appearing bright on T2
- Degenerative change: irregular contour and mild signal increase
STIR:
- Ligament: intermediate-to-dark signal
- Edema or enthesopathy: bright hyperintense periligamentous signal
- Effective in detecting early soft-tissue injury or inflammation
Proton Density Fat-Saturated (PD FS):
- Normal: low signal (dark) band
- Partial tear or strain: focal bright hyperintensity along course of ligament
- Highlights subtle periligamentous fluid and inflammatory changes
T1 Fat-Sat Post-Contrast:
- Normal: no significant enhancement
- Inflamed or scarred ligament: focal or diffuse enhancement
- Postoperative or chronic cases: peripheral rim enhancement around fibrotic tissue

CT Appearance

Non-Contrast CT:

Ligament not distinctly visualized; appears as a thin soft-tissue band connecting pisiform to base of fifth metacarpal
Pisiform and metacarpal margins: sharply defined cortical outlines
Calcification or ossification: seen as dense linear or nodular foci along the ligament
Useful for evaluating bony avulsion, degenerative change, or pisiform fracture

Post-Contrast CT (standard):

Limited value for ligament itself; may show enhancement of inflamed or thickened tissue
Highlights periligamentous soft-tissue swelling or adjacent synovitis

CT Arthrography Appearance

Contrast outlines the fifth carpometacarpal joint and adjacent capsule
Normal ligament: appears as a thin non-opacified band connecting pisiform to fifth metacarpal
Tear or attenuation: contrast leaks along the ligament’s course or extends into periligamentous tissues
Chronic degeneration: shows irregular ligament contour or partial contrast infiltration without full discontinuity
Helpful for assessing ulnar wrist instability, FCU-related injuries, and small avulsion defects