Palmaris longus muscle

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Palmaris longus muscle
Antagonist
Extensor carpi radialis brevis, Extensor carpi radialis longus, Extensor carpi ulnaris
Identifiers
Latinmusculus palmaris longus
GreekΜακρύς παλαμικός μυς
TA98A04.6.02.029
TA22482
FMA38462
Anatomical terms of muscle]

The palmaris longus is a

flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; this number can vary in African, Asian, and Native American populations, however.[1] Absence of the palmaris longus does not have an effect on grip strength.[2] The lack of palmaris longus muscle does result in decreased pinch strength in fourth and fifth fingers. The absence of palmaris longus muscle is more prevalent in females than males.[3]

The palmaris longus muscle can be seen by touching the pads of the fourth finger and thumb and flexing the wrist. The tendon, if present, will be visible in the midline of the anterior wrist.

Structure

Palmaris longus is a slender, elongated, spindle shaped muscle, lying on the medial side of the flexor carpi radialis. It is widest in the middle, and narrowest at the proximal and distal attachments.[4]

It arises mainly from the medial epicondyle of the humerus via the common flexor tendon. It also takes origin from the adjacent intermuscular septa and from the antebrachial fascia.[4]

It ends in a slender, flattened tendon, which passes over the upper part of the flexor retinaculum and inserts onto the central part of the flexor retinaculum and lower part of the palmar aponeurosis. Frequently, it sends a tendinous slip to the short muscles of the thumb.[4]

Nerve supply

The palmaris longus is innervated by the median nerve.[5]

Variation

Palmaris Longus: misplaced or absent
The fleshy belly occasionally migrates distally and comes to lie close above the wrist, as here.
Palmaris Longus was absent in 98 of 716 dissected limbs (i.e., in 13.7% of 358 paired limbs, 26 times in both limbs, 26 in the right only, and 20 in the left only. (R. K. George).[6]

The palmaris longus muscle is a variable muscle. The most common variation is its absence. Several in vivo and in vitro studies have documented the prevalence or absence of the PL tendon in different ethnic groups. Between 5.5 and 24% of Caucasian populations (European and North American) and 4.6 to 26.6% of Asian populations (Chinese, Japanese, Indian, Turkish, Malaysian) have been reported to lack the PL tendon.[7]

There are also variations related to its form. It may be tendinous above and muscular below; or it may be muscular in the center with a tendon above and below; or it may present two muscular bundles with a central tendon; or finally it may consist solely of a tendinous band. The muscle may be double, or missing entirely. Slips of origin from the

scaphoid, and into the muscles of the little finger
have been observed.

Clinical significance

Use in tendon grafts

Cross-section through the middle of the forearm

The palmaris longus muscle is the most popular for use in tendon grafts for the wrist due to the length and diameter of the palmaris longus tendon, and the fact that it can be used without producing any functional deformities. When a tendon becomes ruptured in the wrist, the palmaris longus tendon may be removed from the

flexor pollicis longus tendon.[8]

The palmaris longus muscle itself is a weak flexor, and provides no substantial flexing force that would inhibit movement in the wrist if its tendon were cut and moved elsewhere. The palmaris longus may contribute and assist in thumb abduction movements; an action necessary to open the hand.

plantaris muscle in the leg may be taken instead.[11]
Using the patient’s own tendon is advantageous, as it does not introduce foreign material into the body.

Carpal tunnel syndrome and palmaris longus variants

Of the known anatomical variants of the palmaris longus, the reverse belly of the palmaris longus may be localized within the carpal tunnel producing symptoms of carpal tunnel syndrome. Knowledge of this variation is important to prevent unnecessary carpal tunnel release surgery, in which the median nerve compression may remain unresolved due to the presence of this palmaris longus variant.[12]

Other animals

Evolution

The evolutionary interpretation of the muscle's absence is that humans inherited the muscle through common descent, and numerous animals that humans share a common ancestor with (such as the orangutan) still actively employ the muscle.[13] Close primate relatives (such as the chimpanzee and gorilla) also do not actively employ the muscle, and hence they also demonstrate the same variability.[14] The common descent principle suggests that at some stage our ancestors employed the muscle actively. The thumb apparatus (and particularly the thenar muscle group) then started developing in the hominin branch, and consequently the Palmaris longus became vestigial. As there is no apparent evolutionary pressure (positive or negative) concerning the muscle, it has remained largely unaffected by evolutionary processes.[15]

See also

This article uses anatomical terminology.

References

Public domain This article incorporates text in the public domain from page 446 of the 20th edition of Gray's Anatomy (1918)

  1. S2CID 12394636
    .
  2. S2CID 35394120
    .
  3. PMID 24426922
    .
  4. ^ a b c Gray's Anatomy (1918), see infobox
  5. ISBN 978-0-8089-2306-0
    .
  6. ^ Grant's Atlas of Anatomy. 1962.
  7. S2CID 26235241
    .
  8. PMID 19753215
    .
  9. S2CID 21747288
    .
  10. PMID 32790091
    .
  11. ^ Wheeless, Clifford R (December 2009). "Palmaris Longus Tendon Graft Harvest". Wheeless' Textbook of Orthopaedics. Retrieved February 25, 2012.
  12. S2CID 26397516
    .
  13. ^ "Proof of evolution that you can find on your own body". 17 March 2016.
  14. ^ Thejodhar et al, Indian J Plast Surg Vol 41.1 (2008)
  15. ^ Maughan et al: The Roles of Mutation Accumulation and Selection in Loss of Sporulation in Experimental Populations of Bacillus subtilis Genetics. 2007 Oct;177(2):937-48

External links

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