Abductor digiti minimi muscle of hand
|Abductor digiti minimi muscle of hand|
|Origin||Pisiform bone, the pisohamate ligament, and the flexor retinaculum|
|Insertion||Base of the proximal phalanx of the 5th digit on the ulnar or medial side|
|Nerve||Deep branch of ulnar nerve|
|Actions||Abducts little finger|
|Latin||Musculus abductor digiti minimi manus|
|Anatomical terms of muscle|
In human anatomy, the abductor digiti minimi (abductor minimi digiti, abductor digiti quinti, ADM) is a skeletal muscle situated on the ulnar border of the palm of the hand. It forms the ulnar border of the palm and its spindle-like shape defines the hypothenar eminence of the palm together with the skin, connective tissue, and fat surrounding it. Its main function is to pull the little finger away from the other fingers (i.e. abduction).
Its distal tendon ends in three slips that are inserted into the ulnopalmar margin of the proximal phalanx, the palmar plate of the metacarpophalangeal joint, and the sesamoid bone when present. Some fibers insert into the finger's dorsal aponeurosis, 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. 
The abductor digit minimi develops at an early stage from an ulnar muscle primordium of the superficial layer of the original undifferentiated mesenchyme of the hand, together with the flexor digitorum superficialis (medial primordia) and the abductor pollicis brevis (radial). In contrast, the remaining hypothenar muscles are derived from the deep layer at a later stage. 
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 retinaculum, the fascia of the distal forearm, or the tendon of the palmaris longus. Occasionally, the muscle is partially inserted onto the fifth metacarpal bone.
In case of polydactyly it may insert to the sixth finger instead, if there is one.
It plays an important role when the hand is grasping large objects with outspread fingers. 
- Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol. 1: Locomotor System (5th ed.). Thieme. p. 178. ISBN 3-13-533305-1.
- Schmidt, Hans-Martin; Lanz, Ulrich (2003). Surgical Anatomy of the Hand. Thieme. p. 125. ISBN 1-58890-007-X.
- Sanudo, JR; Mirapeix, RM; Ferreira, B (1993). "A rare anomaly of abductor digiti minimi". J. Anat. 182 ( Pt 3) (182): 439–442. PMC 1259818. PMID 8226300.
- Claassen H, Schmitt O, Schulze M, Wree A (December 2013). "Variation in the hypothenar muscles and its impact on ulnar tunnel syndrome". Surg Radiol Anat. 35 (10): 893–9. doi:10.1007/s00276-013-1113-5. PMID 23558800.
- Doyle, James R.; Botte, Michael J. (2003). Surgical anatomy of the hand and upper extremity. Lippincott Williams & Wilkins. pp. 155–156. ISBN 0-397-51725-4.
- Origin, insertion and nerve supply of the muscle at Loyola University Chicago Stritch School of Medicine
- Palastanga, Nigel; Field, Derek; Soames, Roger (2006). Anatomy and human movement: structure and function. Elsevier Health Sciences. p. 112. ISBN 0-7506-8814-9.