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Flexor Digiti Minimi (FDM)

OVERVIEW
Other Name:
Flexor digiti minimi brevis, flexor digiti quniti, flexor digiti quinti brevis.
 
Key Points:
• Flexes the small finger at metacarpal-phalangeal joint.
• Hypothenar eminence muscle (an intrinsic hand muscle).

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EXAMINATION
Muscle Function:
Primary: Flexion at the metacarpal-phalangeal joint of the small finger.
Secondary: Assists in small finger opposition towards thumb.
Palpation: Within in the hypothenar eminence during small finger flexion at the metacarpal-phalangeal joint.
 
Strength Testing: Position – hand in supination.  Stabilize – the hand.  Resist – small finger metacarpal-phalangeal flexion by applying force over palmar proximal phalanx (in the direction of extension).
 
Possible Substitutions: Opponens digiti minimi and the lumbricals.
 
Relevant Anatomy:
Innervation:
• Roots: C8, T1.
• Nerve: Ulnar, deep motor branch.
• Innervation Route: C8, T1 → ulnar nerve → deep motor branch → flexor digiti minimi branch.
Origins: Hook of the hamate and flexor retinaculum.
 
Insertion: Small finger ulnar tubercle at base of proximal phalanx, ulnar side of metacarpal phalangeal joint palmar plate, and sesamoid (if present).