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The palmaris longus muscle is a variable muscle located centrally in the anterior forearm. It is visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris. The most common variation of this muscle is its absence, with studies reporting rates of absence ranging from 10-20% in the general population. The palmaris longus is also known to exhibit a high degree of anatomical variation in individuals who do possess the muscle. It is the most popular muscle for use in tendon grafts for the wrist due to its length and diameter, and the fact that it can be removed without causing functional deformities.
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What You'll Learn
Palmaris longus muscle absence
The palmaris longus is a variable muscle that is not always present in the human body. It is a slender, superficial flexor muscle of the forearm that aids the flexor carpi ulnaris and flexor carpi radialis muscles in flexing the hand on the wrist. It also helps to stabilize the elbow joint when fully extended. The absence of the palmaris longus does not affect grip strength. The most common variation of this muscle is its absence, which has been observed in various ethnic groups with rates ranging from 1.5% to 63.9% across different populations.
The muscle can be absent in one forearm (unilateral) or both forearms (bilateral), and its absence has been shown to vary based on body side, gender, and ethnicity. In a study of 300 Caucasian subjects, the unilateral absence of the palmaris longus was observed in 16% of cases, while the bilateral absence was observed in 9%. Unilateral and bilateral absence was more common in males, and the right side was more commonly affected in those with unilateral absence.
The evolutionary interpretation of the muscle's absence suggests that humans inherited the muscle through common descent. Many animals that humans share a common ancestor with, such as the orangutan, still actively employ the muscle. However, close primate relatives like chimpanzees and gorillas also demonstrate the same variability, as they do not actively use the muscle.
The palmaris longus is the most popular muscle for tendon grafts for the wrist due to its length and diameter, and because it can be used without causing functional deformities. If the palmaris longus is not available for harvesting, the anatomically homologous plantaris muscle in the leg may be used instead.
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Palmaris longus tendon grafts
The palmaris longus is a variable muscle, and its absence is the most common variation. It is estimated that the palmaris longus muscle is absent in around 10-20% of the general population, although this rate varies across different ethnic groups. For instance, the prevalence of absence is higher in Caucasians (22.4%) and Turks (63.9%), while it is lower in Blacks (3%), Asians (4.8%), and Koreans (0.6%).
The palmaris longus muscle is located centrally in the anterior forearm, and it aids in the flexion of the hand on the wrist. It also helps to stabilize the elbow joint when fully extended. The muscle is visible as a small tendon located between the flexor carpi radialis and the flexor carpi ulnaris. The tendon has a paratenon, which does not promote gliding as well as intrasynovial tendons.
Due to its length, diameter, and accessibility, the palmaris longus tendon is the most popular choice for tendon grafts in the wrist. The tendon can be used without causing any functional deformities, and it offers approximately 15 cm of graft length. The use of the patient's own tendon is advantageous as it does not introduce foreign material into the body.
When considering a palmaris longus tendon graft, it is important to determine the presence and thickness of the tendon preoperatively. This can be done through clinical tests and palpation. If the tendon is indicated to be small, the patient should be informed that a graft may need to be harvested from another area of the body. During the surgical procedure, transverse wrist incisions are made to identify and isolate the tendon.
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Palmaris longus evolutionary interpretation
The palmaris longus muscle is a slender, elongated, spindle-shaped muscle located centrally in the anterior forearm. It is visible as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris muscles. The palmaris longus is a variable muscle, with its most common variation being its absence. Studies have shown that the palmaris longus is absent in around 10-20% of the general population, with the rate varying across different ethnic groups. For example, between 5.5 and 24% of Caucasian populations and 4.6 to 26.6% of Asian populations have been reported to lack the palmaris longus tendon.
The evolutionary interpretation of the muscle's absence suggests that humans inherited the muscle through common descent. Several animals that humans share a common ancestor with, such as the orangutan, still actively employ the muscle. On the other hand, close primate relatives like chimpanzees and gorillas also demonstrate the same variability, with the muscle being absent in some individuals.
The palmaris longus muscle is the most commonly used for tendon grafts in the wrist due to its length and diameter, and because it can be harvested without causing any functional deformities. The muscle is also known to assist in thumb abduction movements, which are necessary for opening the hand. Additionally, it helps in tightening and tensing the palmar aponeurosis and acts as an anchor for the skin and fascia of the hand, resisting horizontal shearing forces in the distal direction.
In terms of evolutionary transformation, the palmaris longus muscle has been studied in the context of the development of styliform cartilage in flying squirrels. The muscle's role in gliding membrane support has been a long-standing topic of interest in squirrel evolution and development.
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Palmaris longus muscle detection
The palmaris longus muscle is a long, slender muscle usually present in the superficial volar compartment of the forearm. It is located centrally in the anterior forearm, extending from the distal humerus to the root of the hand. It is also known as an accessory muscle.
The palmaris longus is a variable muscle, and its most common variation is its absence. Studies have shown that the palmaris longus muscle may be missing entirely in almost 30% of the population, although the rate varies in different ethnic groups. 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.
The palmaris longus is the most popular muscle for use in tendon grafts for the wrist due to its length and diameter, and the fact that it can be used without producing any functional deformities. It is also used in surgical procedures to correct claw-finger deformities, as it is long enough and its tendon fibres are parallel and loosely held.
Several clinical tests have been developed to accurately detect the palmaris longus muscle. These tests rely on certain positions of the wrist and hand to put the muscle in a state of tension so that its tendon is both visible and palpable. For example, one test involves maintaining the forearm at 90 degrees, followed by moving the thumb in opposition towards the little finger with the wrist partially flexed.
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Palmaris longus muscle function
The palmaris longus muscle is a variable muscle, with the most common variation being its absence. It is a long, slender, and elongated muscle of the anterior forearm, extending from the distal humerus to the root of the hand. It sits between the flexor carpi radialis and flexor carpi ulnaris muscles, aiding them in performing a balanced flexion of the hand on the wrist. It also acts to stabilize the elbow joint when fully extended.
The palmaris longus muscle has a relatively short inferior course, giving off a long tendon midway down the forearm. It is the most superficial muscle of the superficial forearm flexors and is innervated by the median nerve. The muscle is visible as a small tendon and can be observed 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.
The specific actions of the palmaris longus muscle include wrist flexion and tensioning the palmar aponeurosis, or the skin and fascia of the hand. It also helps in tightening and tensing up the palmar aponeurosis, acting as an anchor to resist horizontal shearing forces in the distal direction. The muscle is frequently used in tendon grafts for the wrist due to its length and diameter, and because it can be used without causing functional deformities.
The absence of the palmaris longus muscle does not affect grip strength but does result in decreased pinch strength in the fourth and fifth fingers. It is more prevalent in females than males, and its presence or absence varies among different ethnic groups. The evolutionary interpretation of its absence suggests that humans inherited the muscle through common descent, with some animals that share a common ancestor with humans, such as the orangutan, still actively employing the muscle.
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Frequently asked questions
The palmaris longus is a variable muscle located centrally in the anterior forearm. It aids the flexor carpi ulnaris and flexor carpi radialis muscles to perform a balanced flexion of the hand on the wrist. It also helps stabilize the elbow joint when fully extended.
The palmaris longus muscle is not present in everyone. Studies have shown that the muscle is absent in around 10-20% of the general population, although the rate varies in different ethnic groups.
The main function of the palmaris longus muscle is to act as an anchor for the skin and fascia of the hand in resisting horizontal shearing forces in the distal direction. It is also the most popular for use in tendon grafts for the wrist due to its length and diameter.
