Which muscle group of the hand do the palmar interossei belong to?

They belong to the central compartment of the hand muscles, along with the lumbricals (1–4) and dorsal interossei.

What structures form the posterior wall of the central palmar compartment?

The posterior wall is formed by the deep fascia covering the palmar interossei and the horizontal part of the lateral intermuscular septum.

Which nerve innervates these muscles?

All palmar interossei are innervated by the deep branch of the ulnar nerve (ramus profundus n. ulnaris), which enters the sub-tendinous space from the medial side.

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Palmar Interossei Muscles

mm. interossei palmares

For medical students2 min readUpdated 2026-10-10

The palmar interossei muscles (mm. interossei palmares) are three unipennate muscles located in the second, third, and fourth intermetacarpal spaces. They belong to the central compartment of the hand, adduct the fingers toward the third (middle) digit, and assist in flexing the proximal phalanges while extending the middle and distal phalanges.

Number3 muscles (unipennate)

FunctionAdduction of digits II, IV, and V toward digit III

InnervationDeep branch of the ulnar nerve

Location and Topography

The palmar interossei belong to the central compartment of the hand muscles (compartimentum palmaris medius). There are three such muscles in total, situated within the 2nd, 3rd, and 4th intermetacarpal spaces.

The central fascial space of the palm is bordered by four walls:

Anterior wall: Palmar aponeurosis (aponeurosis palmaris).
Lateral wall: Vertical part of the lateral intermuscular septum.
Medial wall: Medial intermuscular septum.
Posterior wall: Deep fascia covering the palmar interossei and the horizontal part of the lateral intermuscular septum.

Structure: Origin and Insertion

The palmar interossei are unipennate muscles. Their anatomical landmarks are:

Origin: Shafts of the second, fourth, and fifth metacarpal bones.
Insertion: Dorsal digital expansions (extensor hoods) and the bases of the proximal phalanges of digits II, IV, and V; the fibers are directed toward the axial (third) digit.

Biomechanics and Functions

Adduction: Adducts digits V, IV, and II toward the midline axis represented by digit III.
Flexion and Extension: Flexes the proximal phalanx and extends the middle and distal phalanges.

Innervation

All interossei muscles of the hand—both palmar and dorsal—are innervated by the deep branch of the ulnar nerve (ramus profundus n. ulnaris).

The deep branch of the ulnar nerve enters the sub-tendinous space of the central compartment from the medial side.

It also innervates the 3rd and 4th lumbricals, the adductor pollicis, and the deep head of the flexor pollicis brevis.

Note: Other Meanings of PAD

In medical literature, the acronym PAD serves as a mnemonic for the palmar interossei, but has other contexts:

Padua Prediction Score: Used to assess the risk of venous thromboembolism in hospitalized medical patients, including acute exacerbations of Crohn's disease, and to evaluate risk during menopausal hormone therapy continuation. The PADUA system is also used to evaluate the renal rim in renal cell carcinoma.
PAD Regimen: Bortezomib + doxorubicin + dexamethasone; recommended for plasma cell leukemia and listed among treatment regimens for multiple myeloma.

Mnemonic

To remember the function of the interossei muscles, the 'DAB–PAD' rule is useful. PAD stands for Palmar ADduct: the palmar interossei adduct the fingers toward the third digit. DAB stands for Dorsal ABduct: the dorsal interossei abduct digits II, III, and IV away from the hand axis. A similar rule, Plantar ADduct, applies to the plantar interossei of the foot, which adduct digits III–V toward the axis of the second digit.

Frequently asked questions

Which muscle group of the hand do the palmar interossei belong to?: They belong to the central compartment of the hand muscles, along with the lumbricals (1–4) and dorsal interossei.
What structures form the posterior wall of the central palmar compartment?: The posterior wall is formed by the deep fascia covering the palmar interossei and the horizontal part of the lateral intermuscular septum.
Which nerve innervates these muscles?: All palmar interossei are innervated by the deep branch of the ulnar nerve (ramus profundus n. ulnaris), which enters the sub-tendinous space from the medial side.

Go deeper

Dorsal interossei muscles of the hand (mm. interossei dorsales)
Lumbrical muscles of the hand (mm. lumbricales)
Central compartment of the palm (compartimentum palmaris medius)
Deep branch of the ulnar nerve (r. profundus n. ulnaris)