Palmaris longus muscle
|Palmaris longus muscle|
|Front of right upper extremity. (Palmaris longus labeled at bottom, second from left.)|
|Transverse section across distal ends of radius and ulna. (Palmaris longus labeled at center top.)|
|Latin||musculus palmaris longus|
|Gray's||subject #125 446|
|Origin||medial epicondyle of humerus (common flexor tendon)|
|Antagonist||Extensor carpi radialis brevis, Extensor carpi radialis longus, Extensor carpi ulnaris|
The palmaris longus is seen as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. The muscle is absent in about 14 percent of the population, however this varies greatly with ethnicity. Absence of this muscle does not have any known effect on grip strength; however, lack of the palmaris longus muscle is disadvantageous in that its tendon can not be harvested as a graft if necessary. Some evolutionary scientists maintain that as it is no longer needed by humans, evolution is dispensing with the tendon.
The palmaris longus muscle can be palpated by touching the pads of the fifth and first fingers and flexing the wrist. The tendon, if present, will be very visible.
It ends in a slender, flattened tendon, which passes over the upper part of the flexor retinaculum, and is inserted into the central part of the flexor retinaculum and lower part of the palmar aponeurosis, frequently sending a tendinous slip to the short muscles of the thumb.
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. The overall prevalence of the absence of the PL tendon in Caucasian populations (European and North American) has been reported between 5.5 and 24% . On the other hand, the overall prevalence of absence of the PL tendon in Asian populations (Chinese, Japanese, Indian, Turkish, Malaysian) has been reported between 4.6 and 26.6%.  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.
Use in tendon grafts
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.
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 was cut and moved elsewhere. If the palmaris longus muscle is not available for harvesting in an individual, the anatomically analogous plantaris muscle in the leg may be taken instead. Using the patient’s own tendon is advantageous, as it does not introduce foreign material into the body.
- Sebastin, S. J.; Lim, A. Y. T.; Bee, W. H.; Wong, T. C. M.; Methil, B. V. (2005). "Does the absence of the palmaris longus affect grip and pinch strength?". Journal of hand surgery (Edinburgh, Scotland) 30 (4): 406–408. doi:10.1016/j.jhsb.2005.03.011. PMID 15935531.
- Gray's Anatomy (1918), see infobox
- Kose, Ozkan; Adanır O, Cirpar M, Kurklu M, Komurcu M (May 2009). "The prevalence of absence of the palmaris longus: a study in Turkish population.". Arch Orthop Trauma Surg. 129(5): 609–11. doi:10.1007/s00402-008-0631-9.
- Carroll, Will; Gorman, Thomas (June 2009). "Inside Tommy John Surgery". Baseball Prospectus. Retrieved February 2012.
- Thejodhar, P; Potu, Bhagath Kumar; Vasavi, Rakesh G (2008). "Unusual palmaris longus muscle". Indian Journal of Plastic Surgery 41 (1): 95–96. doi:10.4103/0970-0358.41125. PMC 2739544. PMID 19753215.
- Wheeless, Clifford R (1996. Web. 04 Dec. 2009). "Palmaris Longus Tendon Graft Harvest". Wheeless' Textbook of Orthopaedics. Retrieved February 2012.