DORSAL INTEROSSEI: ORIGIN, INSERTION, INNERVATION, FUNCTIONS - ANATOMY AND PHYSIOLOGY - 2025

The dorsal interossei are two muscle groups. One is located in the palm of both hands in the anterior portion and the other in the dorsal metatarsal area of ​​both feet.

The dorsal interossei of the hand are four muscles located in the metacarpal area, in the dorsal area of ​​the palm of the hand. Taking as reference a line that passes through the middle finger, they laterally separate the fingers in an extended position.

Dorsal interosseous muscles of the hand (Source: CFCF via Wikimedia Commons)

Together with the lumbrical muscles and the palmar interossei, these muscles are part of a group of small muscles, but with very important functions and that are inserted in the extensor expansion that covers the tendon of the common extensor muscle of the fingers.

The lumbrical muscles are extensors of the metacarpophalangeal joints; the palmar interossei are adductors, that is, they bring the fingers closer to the middle finger; and the dorsal interossei are abductor, that is, they move the fingers away from the middle finger on either side.

However, there are also dorsal interossei on both feet. These muscles are located between the metatarsal bones, they are also four muscles and they insert in the proximal phalanges, but do not insert in the dorsal extensor expansions of the feet.

Both dorsal interosseous muscles, both those of the hands and the feet, are bipenniform muscles. These are a type of skeletal muscle classified according to its shape, whose muscle fibers are parallel to each other and come out on both sides of a central, feather-shaped tendon.

Origin

The origin is called the fixed insertion of a muscle, that is, that which during the contractile action of the muscle remains immobile. However, this terminology is only descriptive, because there are muscles that fix the joints and both their origin and their insertion are immobile.

Origin of the dorsal interossei of the hands

Each of the dorsal interosseous muscles of the palm of the hand originates from two portions on the adjacent faces of two metacarpal bones.

The first dorsal interosseous of the hand has its insertion of origin in the adjacent areas of the first and second metacarpals, in the lateral and proximal region of both bones.

The second dorsal interosseous of the hand has its insertion of origin in the adjacent areas of the second and third metacarpal, in the lateral and proximal region of both bones.

The third dorsal interosseous of the hand has its insertion of origin in the adjacent areas of the third and fourth metacarpal, in the lateral and proximal region of both bones.

The fourth dorsal interosseous of the hand has its insertion of origin in the adjacent areas of the fourth and fifth metacarpal, in the lateral and proximal region of both bones.

The third toe has a dorsal interosseus on each side, but these two muscles are the only ones that can move this finger to either side.

Origin of the dorsal interossei of the feet

Each of the dorsal interossei of the feet originate in the diaphysis of the adjacent metatarsals. Like those described for the hand, two points of origin are described for each muscle in the proximal and lateral part of the diaphysis of two adjacent metatarsals.

Dorsal interosseous muscles of the foot (Source: Henry Vandyke Carter via Wikimedia Commons)

These insertions of origin occur between the first and second metatarsals, between the second and third, between the third and fourth, and the origin of the fourth interosseus is between the fourth and fifth metatarsal.

Insertion

Dorsal interossei of the hands

The insertion or mobile attachment point of the muscle for the interossei of the hand is located in two areas. Once they leave their origin, they pass behind the deep transverse metacarpal ligament and go towards the extensor expansions of the second, third and fourth fingers.

These muscles are inserted into the extensor expansions of the fingers already named and at the bases of the corresponding proximal phalanges. These are the two insertion zones.

Attachment is through two tendons, one of which inserts into the phalanx below the transverse fibers of the extensor expansion. The other tendon inserts into the extensor expansion.

There are extensions or ramifications of the tendon that join the phalanx and that in turn join the divisions of the extensor tendon. There is also an oblique extension that extends across the anterior aspect of the proximal phalanx and through the fibrous sheath of the terminal tendon.

Dorsal interossei of the feet

In the case of the dorsal interossei of the feet, each muscle, from its origin, is directed towards the base of the proximal phalanx, passing under the deep transverse metatarsal ligament. The tendons of these muscles help to form the capsules of the metatarsophalangeal joints.

The tendons are inserted at the base of the second, third and fourth proximal phalanxes, the first is inserted in the medial area of ​​the second proximal phalanx, while the others do it in the lateral faces of the bases of the corresponding proximal phalanges.

Another insertion site is the aponeurosis of the extensor digiti minimi tendons, but they do not attach to the extensor extensions of the foot.

Innervation

The innervation of the interosseous muscles of the hands is provided by the deep branches of the ulnar nerve. Sometimes, but rarely, the median nerve supplies the first dorsal interosseous of the hand. The deep branch of the lateral plantar or lateral plantar nerve supplies the dorsal interossei of the feet.

Features

The dorsal interosseous muscles of the hand have as a fundamental function the abduction of the fingers in relation to an imaginary line that passes longitudinally and parallel to the third finger, these muscles favor the lateral displacement of the fingers out of this line.

However, they participate in other functions, such as when the distal interphalangeal joint is flexed, the oblique extension of the tendon tightens and flexes the proximal joint. When the proximal joint is extended, the oblique extension extends the distal one.

Likewise, the participation of these muscles in some rotary movements and in the high precision movements executed by the fingers of the hand has been described. The first dorsal interosseous of the hand can be easily palpated and seen if the index finger is abducted against resistance.

The dorsal interossei of the feet participate in the abduction movements of the toes with respect to the axis of the second toe. However, these functions are of little importance. They also act on the flexion movements of the metatarsophalangeal joints.

References

1. Flament, D., Goldsmith, P., Buckley, CJ, & Lemon, RN (1993). Task dependence of responses in first dorsal interosseous muscle to magnetic brain stimulation in man. The Journal of Physiology, 464 (1), 361-378.
2. Gardner, E., J Gray, D., & O'Rahilly, R. (1963). Anatomy: a regional study of human structure. WB Saunders.
3. Netter, FH (1983). The ClBA Collection of Medical Illustrations,
4. Putz, R., & Pabst, R. (2006). Sobotta-Atlas of Human Anatomy: Head, Neck, Upper Limb, Thorax, Abdomen, Pelvis, Lower Limb; Two-volume set.
5. Standring, S. (Ed.). (2015). Gray's anatomy ebook: the anatomical basis of clinical practice. Elsevier Health Sciences.