Abductor Digiti Minimi (manus)

This muscle is occasionally divided into two or even three slips; in other cases it is united with flexor digiti minimi brevis. Its absence has been reported, as has the doubling of the entire hypothenar muscle mass. An accessory head, accessorius ad abductorem digiti minimi manus is frequently present. It may arise from the tendon of flexor capri ulnaris, from the flexor retinaculum, the tendon of palmaris longus, fascia of the forearm, the ulna, or even the radius. Some cases have been reported where the additional head arises above the wrist from the intermuscular fascia beneath either flexor carpi ulnaris or flexor carpi radialis or from the ulna. Passing distally, it may cover the ulnar artery, even compress it, and end in the abductor or flexor digiti minimi brevis. A portion of the muscle is occasionally inserted into the palmar ligament of the metacarpophalangeal joint. Macalister reported the variations in this muscle as follows;

  1. The muscle may have three origins: one from the pisiform, one from the posterior annular ligament, and one from the tendon of extensor carpi ulnaris. This has also been seen by Wood;
  2. Wood found a muscle with a second head arising from the anterior annular ligament, and was separate from the rest of the muscle, as far as the insertion;
  3. Macalister found the muscle split into two parts, and the medial part had an accessory palmaris longus inserted into it;
  4. Macalister has seen it with a doubled insertion, but otherwise single;
  5. It was absent in three of Macalister cases;
  6. It may be inseparable from flexor brevis; and Macalister found it arising only from the pisiform bone.

The accessory abductor digiti minimi may also compress the deep palmer branch of the ulnar nerve. Compression of the ulnar nerve in Guyon's canal occurs when the muscle hypertrophies in the canal or with traumatic compression between the muscle and the pisohamate ligament. The muscle, artery, and ulnar nerve all lie in the narrow confines of the canal of Guyon, which is bounded by the pisiform and hamate bones. A small separate slip may extend from the pisiform bone to a metacarpal bone, forming the pisimetacarpeus muscle.

Pisiuncinatus (pisohamatus) is a small muscle occurring in 2-5% of hands. It extends from the pisiform bone to the hook of the hamate bone. A similar slip may extend from the pisiform bone to the flexor retinaculum.

Syn.: m. abductor digiti quinti.

Accessorius Abductor Digiti Quinti

Laboratory Specimen, University of Iowa

Accessorius Abductor Digiti Quinti

From Calori, 1868

Accessorius ad abductorem digiti minimi manus.

Note that the darkened muscle attached to the tendon of palmaris longus enters the hypothenar muscle mass. The muscle inserts by a long thin tendon onto the base of the fifth metacarpal on its medial side. The muscle traverses the canal of Guyon where it may compress the ulnar artery and ulnar nerve.
From Calori,1868.

Pisiuncinatus (Pisohamatus)

See B: a, tendon of flexor carpi ulnaris; b, abductor digiti minimi; c, flexor digiti minimi; d, opponens digiti minimi; e, pisiuncinatus (pisohamatum); alpha, os pisiform; beta, hamulus ossis hamati.
from Gruber, 1875, 1881.

References

Baumann, J.A. (1947) Valeur, variation, et équivalencies des muscles extenseurs, interosseux, adducteurs et abducteurs de la main et du pied chez l'homme. Acta Anat. 4:10-16.

Bucher, O. (1943) Über die Varietäten des M. abductor digiti quinti. Anat. Anz. 94: 317-324.

Calori, L. (1868) Delle anomalie più importanti di ossa, vasi, nervi, e muscoli occorse nell' ultimo biennio facendo anatomia del corpo umano. Mem. R. Accad. Sci. Istituto di Bologna. S. 2., 8:417-482.

Fahrer, M. and P.J. Millroy. (1981) Ulnar compression neuropathy due to an anomalous abductor digiti minimi - Clinical and anatomic study. J. Hand Surg. 6:266-268.

Gruber, W. (1875) Ein Musculus piso-hamatus beim Menschen. Arch. Anat. Physiol. Wissen. Med. 1875:202-203

Gruber, W. (1881) Über den Arcus tendineus piso-hamatus, und dessen Substituten, den Musculus piso-hamatus. Arch. Path. Anat. Physiol. Klin. Med. 86:19-25.

Gruber, W. (1888) Ein Musculus piso-metacarpeus. Arch. Path. Anat. Physiol. Klin. Med. 114:365-367.

Guyon, F. (1861) Note sur une disposition anatomique propre à la face antérieur cuter de la region du poignet et mon encore décrite. Bull. Soc. Anat. Paris 6:184-186.

Ikeda, A., Nagaoka, A. and M. Kimura. (1958) On the variation of the abductor digiti minimi and the palmaris longus. Hiroshima Daigaku Igakubu Kaibogaku Daiichi Koza Gyosekishu. 2:96-100. In Japanese.

Lahey, M.D. and P.L. Aulicino. (1986) Anomalous muscles associated with compression neuropathies. Orthopaedic Review 15(4) 199/19-28/208.

Lamb, D. (1970) Ulnar nerve compression lesions at the wrist and hand. Hand 2:17-18.

Lane, W.A. (1887) Abnormal muscles of the hand. J. Anat. Physiol. 21:673.

Macalister, A. (1875) Additional observations on muscular anomalies in human anatomy (third series), with a catalogue of muscular variations hitherto published. 25:1-134.

Schjelderup, H. (1964) Aberrant muscle in the hand causing ulnar nerve compression. J. Bone Joint Surg. (B) 46:361.

Stocquart, A. (1882) Quelques anomalies et varietiés anatomique observés sur le vivant et sur le cadaver. J. de Med., de Chir., et de Pharmacology 4:449-453.

Swanson, A.B., Biddulup, S.L., Baughman, F.A. and G. deGroot. (1972) Ulnar nerve compression due to an anomalous muscle in the canal of Guyon. Clin. Orthop. Rel. Res. 83:64-69.

Turner, M.S. and D.M. Caid. (1977) Anomalous muscles and ulnar nerve compression at the wrist. Hand 9:140-142.

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