The extensor medii proprius (so called the ''extensor digiti medii'') is a rare anatomical variant in the extensor compartment of the

forearm The forearm is the region of the upper limb between the elbow and the wrist. The term forearm is used in anatomy to distinguish it from the arm, a word which is used to describe the entire appendage of the upper limb, but which in anatomy, techn ...

. The aberrant muscle is analogous to the

extensor indicis In human anatomy, the extensor indicis (proprius) is a narrow, elongated skeletal muscle in the deep layer of the dorsal forearm, placed medial to, and parallel with, the extensor pollicis longus. Its tendon goes to the index finger, which it ext ...

with the insertion being the middle finger instead of the index finger.

Structure

The extensor medii proprius originates from the distal third of

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

near the

and the adjacent

interosseous membrane An interosseous membrane is a thick dense fibrous sheet of connective tissue that spans the space between two bones, forming a type of syndesmosis joint. Interosseous membranes in the human body: * Interosseous membrane of forearm * Interosseo ...

. It passes through the fourth extensor compartment along with the

and the extensor digitorum. It inserts to the extensor expansion of the middle finger usually on the ulnar side of the tendon of the extensor digitorum of the middle finger, though, insertion deep to the extensor digirorum tendon was seen. Insertion to the

fibrous tissue Connective tissue is one of the four primary types of animal tissue, a group of cells that are similar in structure, along with epithelial tissue, muscle tissue, and nervous tissue. It develops mostly from the mesenchyme, derived from the mesode ...

proximal to the

metacarpophalangeal 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 ...

joint of the middle finger was also reported.

Prevalence

The reported incidence of the extensor medii proprius in cadaveric dissections ranges from 0% to 12%. Meta-analysis showed that the prevalence of this muscle was significantly higher in North American and Japanese populations than European and Indian populations.

Function

The extensor medii proprius extends the middle finger. The presence of this anomalous muscle results in a more independent movement of the middle finger.

Clinical significance

The extensor medii proprius is unlikely to cause

symptoms Signs and symptoms are diagnostic indications of an illness, injury, or condition. Signs are objective and externally observable; symptoms are a person's reported subjective experiences. A sign for example may be a higher or lower temperature ...

. However, awareness of this anomalous muscle may help physicians for identification and for proper planning of surgery.

Additional Images

References

External links

* {{Use dmy dates, date=April 2017 Muscles of the upper limb Anatomical variations