Anatomy Atlases: Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: P: Palmaris Longus

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Illustrated Encyclopedia of Human Anatomic Variation: Opus I: Muscular System: Alphabetical Listing of Muscles: P

Palmaris Longus

Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed

This is one of the most variable muscles in the body. It is absent in 11.2% of bodies (all sources) but has been reported absent in only about 5 % of Japanese and 2.2 % of chinese. Its absence was, reportedly, recorded as early as 1559 by Colombus (De Re Anatomica Libri). In a splendid recent review however, on the absence of palmaris longus, Brinkman and Hage (2015) reported that Vesalius (De Fabrica) actually described this variation 16 years before Columbus. In an study of 800 living subjects it was absent on both sides in 7.7% of cases, absent on the right in 4.5%, and absent on the left in 5.2%. Palmaris longus is absent more often in females and on the left side in both sexes. In another study of 276 cadavers (George) palmaris longus was present on both sides in 216 (7 females) or 78.3%, present on the right side only 17 or 6.1%, present on the left only in 19 (2 females) or 6.9%, and absent on both sides in 24 (3 females) or 8.7%. Hence, palmaris longus was absent in 15.2% of these 552 limbs, slightly more frequently in the right limb (15.6%) than in the left (14.9%). Mori reported on studies in the Japanese population as follows: Adachi reported palmaris longus absent in 2.7-3.9%, Koganei and Arai 3.9%, Shikinami 3.9%, Matsushima 3.2%, Inoue 8.0%, Taketa 3.7%, Suzuki 1 males 3.6%, females 6.0%, Suzuki 2 males 7.0%, females 6.0%, and Suzuki 3 males 5.5%, females 9.5%.

It was shown that there was no correlation between the presence or absence of palmaris longus and plantaris muscles. If it is desirable to estimate the probability of the presence or absence of palmaris longus knowledge of the presence or absence of plantaris is of no help. The two muscles vary independently.This may be unfortunate for those needing tendon repairs. Palmaris longus may be digastric or fleshy throughout its entire length. It may have a proximal tendon as well as a distal one; it may be fleshy distally and tendinous proximally (palmaris inversus); or it may be reduced to a mere tendinous band.

Occasionally, there are two palmaris muscles, one having the usual form and the other one of the forms referred to above, or one of the following additional modes of origin. The muscle may arise from the medial intermuscular septum, the biceps or brachialis, the lacertus fibrosus, the fascia of the forearm proximally, or one of the neighboring muscles, the coronoid process, or the radius. The muscle may be doubled with the belly of one next to the point of insertion of the second and the second with its belly adjacent to the tendon of origin of the first muscle. The muscle may also be doubled at its proximal end, the additional slip arising from one of the sites just indicated above.

The insertion is equally variable. It may be attached to the fascia of the forearm, tendon of the flexor carpi ulnaris, flexor retinaculum (above or beneath), pisiform bone, scaphoid bone, the middle phalanx of the fourth digit (replacing the usual flexor digitorum superficialis slip), short abductor of the thumb, fascia and muscles of the hypothenar eminence, one of the flexor tendons, or the vicinity near a metacarpophalangeal joint.

Palmaris longus may enter Guyon's canal (the space between the pisiform bone and the hook of the hamate bone) and compress the ulnar artery and nerve located therein. Its tendon of insertion may be split into two or more bundles, in which case the accessory tendon or tendons may be inserted into one of the structures named above. The tendon of palmaris longus may enter and traverse the carpal tunnel, and may compress the median nerve in its course, before inserting below the palmar fascia. Palmaris longus and its tendon may substitute for the ring finger slip of flexor digitorum superficialis.

Palmaris longus variations have been classified as:

complete agenesis,
variation in location and form of its fleshy part,
aberrancy of attachment at its origin or insertion,
duplication and triplcation,
accessory slips, and
replacing elements of a similar form or position.

Palmaris profundus is a muscle arising from the lateral edge of the radius, in its middle third, lateral to flexor digitorum superficialis and deep to pronator teres. Its tendon passes beneath the flexor retinaculum (carpal canal or tunnel) (to the radial side of the median nerve) and broadens in the palm of the hand to insert into the deep side of the palmar aponeurosis. The median nerve and the tendon of palmaris profundus are ensheathed in a common sheath of connective tissue. The name, musculus comitans nervi mediani (palmaris profundus) has been suggested for this variant because of its intimate association with the median nerve. The musculus comitans nervi mediani may be fleshy proximally or fleshy distially; the muscle appears to mimic palmaris longus in its form and variations. The tendinous origin of musculus comitans nervi mediani has been implicated in, the proximal forearm, as a cause of the compressive neuropathy of the anterior interosseous nerve syndrome and, in the distal forearm and wrist , as the muscle passes through the carpal canal, with the carpal tunnel syndrome.

The tendon of palmaris longus may give rise to an additional muscle, accessorius ad flexorem digiti minimi, which usually inserts on the body and head of the fifth metacarpal between abductor digiti minimi and flexor digiti minimi brevis. It has been reported that an accessorius may have two bellies, one arising from the tendon of flexor carpi ulnaris and the other arising from the tendon of palmaris longus.

A forearm with three palmaris longus muscles has been recorded.

Syn.: m. Langer Hohlhandmuskel, Handsehnenspanner, Palmaire grèle (Cruveilhier).

Varieties of Palmaris Longus.
from Reimann, et al.

Varieties of Palmaris Longus.
from Gruber, 1868, 1872.

Varieties of Palmaris longus.
from Gruber, 1868, 1872.

Doubled Palmaris Longus with a Flexor Digiti Minimi Accessorius.
from Saadeh and Bergman.

Palmaris Longus

Palmaris longus substituting for the ring finger slip of flexor digitorum superficialis.
Labaratory specimen, University of Iowa.
From Cassell and Bergman. (1990)

Musculus comitans nervi mediani s. palmaris profundus.
Two examples of musculus comitans nervi mediani (m. palmaris profundus). In the upper diagram the muscle belly is proximal and in the lower the diagram the muscle belly is distally located. The median nerve and the anomalous muscles are contained in a common fascial sheath. In the diagrams, the sheath is not seen at the two ends of the illustration. In both cases, parts of the muscle enter the carpal canal, i.e. either the distal tendon or the distal muscle belly or its tendon. A and C show a cut line through the proximal part of the sheath depicting the relationship of muscle and nerve. In B and D, the cut line shows the muscle and nerve, distially, in the carpal canal. It is a B an D that the unyielding transverse carpal ligament may compress and functionally alter the median nerve. The lowest placed illustration is of the carpal canal. MN: median nerve, PP (CNM): muscle belly, T: tendon of muscle.
From Sahinoglu, Cassell, Miyauchi, and Bergman

Musculus Comitans Nervi Mediani s. Palmaris Profundus
from Sahinoglu, et al., 1994

Palmaris longus with and associated accessorius as flexorem digiti minimi muscle.
From Calori, 1867

References

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