Palmaris longus muscle

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Palmaris longus muscle
PL Tendon.png
Palmaris longus tendon as seen in surface anatomy
Details
Origin medial epicondyle of humerus (common flexor tendon)
Insertion palmar aponeurosis and flexor retinaculum of the hand
Artery ulnar artery
Nerve median nerve
Actions wrist flexor
Antagonist Extensor carpi radialis brevis, Extensor carpi radialis longus, Extensor carpi ulnaris
Identifiers
Latin musculus palmaris longus
Greek Μακρύς παλαμικός μυς
TA A04.6.02.029
FMA 38462
Anatomical terms of muscle

The palmaris longus is a muscle visible as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. It is absent in about 14 percent of the population; however, this number varies greatly in African, Asian, and Native American populations.[1] Absence of the palmaris longus does not have an effect on grip strength.[2]

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. This is called schaeffer's test

Structure[edit]

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.[3]

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.[3]

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.[3]

Nerve supply[edit]

The palmaris longus is supplied by the median nerve.[4]

Variation[edit]

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).[5]

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 of 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.[6]

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 coronoid process or from the radius have been seen. Partial or complete insertion into the fascia of the forearm, into the tendon of the flexor carpi ulnaris and pisiform bone, into the scaphoid, and into the muscles of the little finger have been observed.

Clinical significance[edit]

Use in tendon grafts[edit]

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 retinaculum and grafted to take the place of the ruptured tendon. The tendons most commonly replaced or supplemented by the palmaris longus tendon when ruptured are the long flexors of the fingers and the flexor pollicis longus tendon.[7]

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[8]. If the palmaris longus muscle is not available for harvesting in an individual, the anatomically homologous plantaris muscle in the leg may be taken instead.[9] Using the patient’s own tendon is advantageous, as it does not introduce foreign material into the body.

Other animals[edit]

Evolution[edit]

The evolutionary interpretation of the muscle's absence is fairly simple.[10] Humans inherited the muscle through common descent, and numerous animals that we share a common ancestor with (such as the orangutan) still actively employ the muscle. Close primate relatives (such as the chimpanzee and gorilla) also do not actively employ the muscle, and hence they also demonstrate the same variability.[11] The common descent principle suggests that at some stage our ancestor employed the muscle actively. The primate branch then began to evolve the thumb apparatus (and particularly the thenar muscle group) and consequently the Palmaris longus became vestigial. As there is no apparent pressure (positive or negative) concerning the muscle, evolution has largely left it alone.[12] Its persistence might possibly be due to the fact that the necessary changes to the gene(s) involved in losing the muscle may have other consequences, but this is only speculation.

See also[edit]

References[edit]

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

  1. ^ Sebastin SJ, Puhaindran ME, Lim AY, Lim IJ, Bee WH (October 2005). "The prevalence of absence of the palmaris longus--a study in a Chinese population and a review of the literature". Journal of Hand Surgery. 30 (5): 525–7. doi:10.1016/j.jhsb.2005.05.003. PMID 16006020. 
  2. ^ Sebastin SJ, Lim AY, Bee WH, Wong TC, Methil BV (August 2005). "Does the absence of the palmaris longus affect grip and pinch strength?". Journal of Hand Surgery. 30 (4): 406–8. doi:10.1016/j.jhsb.2005.03.011. PMID 15935531. 
  3. ^ a b c Gray's Anatomy (1918), see infobox
  4. ^ Drake, Richard L.; Vogl, Wayne; Mitchell, Adam W. M. (2005). Gray's anatomy for students. Philadelphia: Elsevier/Churchill Livingstone. p. 693. ISBN 978-0-8089-2306-0. 
  5. ^ Grant's Atlas of Anatomy. 1962. 
  6. ^ Kose O, Adanir O, Cirpar M, Kurklu M, Komurcu M (May 2009). "The prevalence of absence of the palmaris longus: a study in Turkish population". Archives of Orthopaedic and Trauma Surgery. 129 (5): 609–11. doi:10.1007/s00402-008-0631-9. PMID 18418616. 
  7. ^ Thejodhar P, Potu BK, Vasavi RG (January 2008). "Unusual palmaris longus muscle". Indian Journal of Plastic Surgery. 41 (1): 95–6. doi:10.4103/0970-0358.41125. PMC 2739544Freely accessible. PMID 19753215. 
  8. ^ Moore, Colin W.; Fanous, Jacob; Rice, Charles L. (27 December 2017). "Revisiting the functional anatomy of the palmaris longus as a thenar synergist". Clinical Anatomy. doi:10.1002/ca.23023. 
  9. ^ Wheeless, Clifford R (December 2009). "Palmaris Longus Tendon Graft Harvest". Wheeless' Textbook of Orthopaedics. Retrieved February 2012.  Check date values in: |accessdate= (help)
  10. ^ "Proof of evolution that you can find on your own body". 
  11. ^ Thejodhar et al, Indian J Plast Surg Vol 41.1 (2008)
  12. ^ 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[edit]