Location and borders
The abductor digiti minimi muscle (m. abductor digiti minimi) is located in the medial compartment of the palm (compartimentum palmaris medialis), which pertains to the hypothenar eminence (hypothenar).
Borders of this fascial compartment:
- Anteriorly and medially: fascia of the palm attached to the 5th metacarpal bone.
- Posteriorly: 5th metacarpal bone.
- Laterally: medial intermuscular septum.
In the medial compartment, there are also the opponens digiti minimi muscle (m. opponens digiti minimi) and the flexor digiti minimi brevis muscle (m. flexor digiti minimi brevis).
Innervation and function
The function of the muscle is abduction of the little finger.
Spinal segments C8–Th1 are indicated for this muscle. It belongs to the group of muscles whose weakness is observed in ulnar nerve (n. ulnaris) lesions.
Clinical significance: why do neurologists test this muscle?
The abductor digiti minimi muscle is evaluated during the examination of muscles innervated by the ulnar nerve.
- Inspection and muscle strength: With the progression of neuropathy, weakness is observed in the muscles innervated by the ulnar nerve, including the abductor digiti minimi, the 1st dorsal interosseous muscle, and other interosseous muscles, while strength in other groups remains preserved. It is recommended to evaluate for hypotrophy (atrophy) in the ulnar nerve innervation zone of the hand. Strength is graded using the MRC (Medical Research Council) scale. A characteristic sign is the "claw hand" deformity.
- Additional tests: If a lesion in Guyon's canal is suspected, the function of the superficial cutaneous branch of the ulnar nerve is assessed and the hypothenar skin wrinkling test is performed. Froment's sign is also checked to detect weakness of the 1st dorsal interosseous muscle.
- Needle electromyography (nEMG): Examination of the abductor digiti minimi muscle is used to detect acute or chronic denervation-reinnervation (axonal) processes. For comparison, thenar muscles innervated by the median nerve are also examined. The study is used for differential diagnosis with motor neuron disease (MND), plexopathies, C8–Th1 spinal cord and root lesions, Hirayama disease, distal forms of spinal amyotrophy, and distal myopathies.
Do not confuse with: the muscle of the same name in the foot
In the lower extremity, there is the abductor digiti minimi muscle of the foot (m. abductor digiti minimi). It is located in the lateral fascial compartment of the sole, which is bounded by the plantar fascia, lateral intermuscular septum, cuboid, and 5th metatarsal bones, and forms the lateral border of the foot. This compartment also contains the flexor digiti minimi brevis of the foot and the opponens digiti minimi.
Class and exam questions
In which fascial compartment of the hand is this muscle located?
It is located in the medial compartment of the palm (compartimentum palmaris medialis). This space is bounded by the palmar fascia, the 5th metacarpal bone, and the medial intermuscular septum.
A lesion of which nerve causes atrophy of the abductor digiti minimi muscle?
Atrophy and weakness of this muscle are observed in ulnar nerve lesions, including suspected entrapment in Guyon's canal. A characteristic sign is the "claw hand" deformity.
What is the purpose of needle EMG of this muscle?
The examination helps detect a denervation-reinnervation process (axonal lesion) and perform differential diagnosis with motor neuron disease (MND), plexopathies, and C8–Th1 root lesions.
What else to study on this topic
- Ulnar nerve (n. ulnaris)
- Medial compartment of the palm (hypothenar)
- Opponens digiti minimi muscle
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