human anatomy The human body is the structure of a human being. It is composed of many different types of cells that together create tissues and subsequently organ systems. They ensure homeostasis and the viability of the human body. It comprises a he ...

, the abductor digiti minimi (abductor minimi digiti, abductor digiti quinti, ADM) is a

skeletal muscle Skeletal muscles (commonly referred to as muscles) are organs of the vertebrate muscular system and typically are attached by tendons to bones of a skeleton. The muscle cells of skeletal muscles are much longer than in the other types of muscl ...

situated on the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

r border of the palm of the

hand A hand is a prehensile, multi-fingered appendage located at the end of the forearm or forelimb of primates such as humans, chimpanzees, monkeys, and lemurs. A few other vertebrates such as the koala (which has two opposable thumbs on each "h ...

. It forms the ulnar border of the

palm Palm most commonly refers to: * Palm of the hand, the central region of the front of the hand * Palm plants, of family Arecaceae **List of Arecaceae genera * Several other plants known as "palm" Palm or Palms may also refer to: Music * Palm (ba ...

and its spindle-like shape defines the

hypothenar eminence The hypothenar muscles are a group of three muscles of the hand, palm that control the motion of the little finger. The three muscles are: * Abductor minimi digiti muscle (hand), Abductor digiti minimi * Flexor digiti minimi brevis (hand), Flexor ...

of the palm together with the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...

connective tissue Connective tissue is one of the four primary types of animal tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesenchyme derived from the mesoderm the middle embryonic germ layer. Connective tiss ...

, and

fat In nutrition science, nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such chemical compound, compounds, most commonly those that occur in living beings or in food. The term often refers spec ...

surrounding it. Its main function is to pull the

little finger The little finger, or pinkie, also known as the baby finger, fifth digit, or pinky finger, is the most ulnar and smallest digit of the human hand, and next to the ring finger. Etymology The word "pinkie" is derived from the Dutch word ''pink ...

away from the other fingers (i.e. abduction).

Structure

The abductor digiti minimi arises from the

pisiform bone The pisiform bone ( or ), also spelled pisiforme (from the Latin ''pisifomis'', pea-shaped), is a small knobbly, sesamoid bone that is found in the wrist. It forms the ulnar border of the carpal tunnel. Structure The pisiform is a sesamoid bone, ...

, the

pisohamate ligament The pisohamate ligament is a ligament in the hand. It connects the pisiform to the hook of the hamate. It is a prolongation of the tendon of the flexor carpi ulnaris. It serves as part of the origin for the abductor digiti minimi. It also forms t ...

, and the flexor retinaculum. Its distal tendon ends in three slips that are inserted into the ulnopalmar margin of the proximal phalanx, the

palmar plate In the human hand, palmar or volar plates (also referred to as palmar or volar ligaments) are found in the metacarpophalangeal (MCP) and interphalangeal (IP) joints, where they reinforce the joint capsules, enhance joint stability, and limit hy ...

of the

metacarpophalangeal joint The metacarpophalangeal joints (MCP) are situated between the metacarpal bones and the proximal phalanges of the fingers. These joints are of the condyloid kind, formed by the reception of the rounded heads of the metacarpal bones into shallow cav ...

, and the

sesamoid bone In anatomy, a sesamoid bone () is a bone embedded within a tendon or a muscle. Its name is derived from the Arabic word for ' sesame seed', indicating the small size of most sesamoids. Often, these bones form in response to strain, or can be pres ...

when present. Some fibers insert into the finger's dorsal

aponeurosis An aponeurosis (; plural: ''aponeuroses'') is a type or a variant of the deep fascia, in the form of a sheet of pearly-white fibrous tissue that attaches sheet-like muscles needing a wide area of attachment. Their primary function is to join musc ...

, which is why the muscle acts similar to a dorsal interosseus muscle. Additionally, the ulnar-most portion of the tendon inserts into the little finger's digital cord, and the muscle thus forms part of a structure that flexes the metacarpophalangeal joint and extends the

interphalangeal joints Interphalangeal joint may refer to: *Interphalangeal articulations of hand The interphalangeal joints of the hand are the hinge joints between the phalanges of the fingers that provide flexion towards the palm of the hand. There are two sets in ...

Innervation

It is innervated by the

deep branch of the ulnar nerve Deep or The Deep may refer to: Places United States * Deep Creek (Appomattox River tributary), Virginia * Deep Creek (Great Salt Lake), Idaho and Utah * Deep Creek (Mahantango Creek tributary), Pennsylvania * Deep Creek (Mojave River tributary), C ...

( C8– T1).

Development

The abductor digit minimi develops at an early stage from an ulnar muscle

primordium A primordium (; plural: primordia; synonym: anlage) in embryology, is an organ or tissue in its earliest recognizable stage of development. Cells of the primordium are called primordial cells. A primordium is the simplest set of cells capable o ...

of the superficial layer of the original undifferentiated

mesenchyme Mesenchyme () is a type of loosely organized animal embryonic connective tissue of undifferentiated cells that give rise to most tissues, such as skin, blood or bone. The interactions between mesenchyme and epithelium help to form nearly every o ...

of the hand, together with the

flexor digitorum superficialis Flexor digitorum superficialis (''flexor digitorum sublimis'') is an extrinsic flexor muscle of the fingers at the proximal interphalangeal joints. It is in the anterior compartment of the forearm. It is sometimes considered to be the deepest pa ...

(medial primordia) and the

abductor pollicis brevis The abductor pollicis brevis is a muscle in the hand that functions as an abductor of the thumb. Structure The abductor pollicis brevis is a flat, thin muscle located just under the skin. It is a thenar muscle, and therefore contributes to the ...

(radial). In contrast, the remaining hypothenar muscles are derived from the deep layer at a later stage.

Variation

In rare cases accessory fascicles of the abductor digiti minimi have been found arising from the

antebrachial fascia The antebrachial fascia (antibrachial fascia or deep fascia of forearm) continuous above with the brachial fascia, is a dense, membranous investment, which forms a general sheath for the muscles in this region; it is attached, behind, to the olec ...

, the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

, and the

. The abductor digiti minimi is the most variable hypothenar muscle, and might be joined by accessory slips from the tendon of the

flexor carpi ulnaris The flexor carpi ulnaris (FCU) is a muscle of the forearm that flexes and adducts at the wrist joint. Structure Origin The flexor carpi ulnaris has two heads; a humeral head and ulnar head. The humeral head originates from the medial epicondyle o ...

, the flexor retinaculum, the fascia of the distal forearm, or the tendon of the

palmaris longus The palmaris longus is a muscle visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; this number can vary in Africa ...

. Occasionally, the muscle is partially inserted onto the fifth metacarpal bone. In case of

polydactyly Polydactyly or polydactylism (), also known as hyperdactyly, is an anomaly in humans and animals resulting in supernumerary fingers and/or toes. Polydactyly is the opposite of oligodactyly (fewer fingers or toes). Signs and symptoms In humans ...

it may insert to the sixth finger instead, if there is one.

Function

It is an abductor of the little finger at the

.Origin, insertion and nerve supply of the muscle
at Loyola University Chicago Stritch School of Medicine It is also possible that the muscle contributes to extension of the middle phalanx of the little finger through its connection to finger's extensor mechanism. It plays an important role when the hand is grasping large objects with outspread fingers.

Etymology

The name is derived from the Latin -''ab'' "away from"; ''ducere'' "to draw"; ''digitus'', "digit"; and ''minimum'', smallest; or ''quintus'', "fifth", meaning "abductor of the smallest or fifth finger".

Additional images

File:Gray422.png, Transverse section across the wrist and digits. File:Hand dissection 6.jpg, Abductor digiti minimi muscle File:Slide1MAI.JPG, Muscles of hand. Cross section.

References

{{Authority control Muscles of the upper limb Abductors (muscles)