Hand Palmaris Longus Muscle – Anatomy, Nerve Supply

Palmaris longus is often described as one of the most random muscles in the human body [rx]. Its absence appears to be hereditary? but the genetic? transmission is not clear [rx]. Its absence can easily be determined clinically; it is easy to harvest and it has a long and flat tendon allowing good revascularization. For these reasons, it is commonly used as a tendon graft by plastic and hand surgeons [rx]. It has also been used for a wide variety of procedures including lip augmentation, ptosis correction, and in the management of facial paralysis? [rx]. Another important attribute of the tendon of the palmaris longus muscle is its somewhat superficial protective role over the median nerve [rx].

Structure of Hand Palmaris Longus Muscle

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.^[rx]

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?.^[rx]

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.^[rx]

Palmaris longus

• Origin: medial epicondyle of humerus via common flexor tendon
• Insertion: palmar aponeurosis and flexor retinaculum
• Action: flexion of the hand
• Innervation: median nerve

Origin and Insertion of Hand Palmaris Longus Muscle

Palmaris longus muscle originates from the medial epicondyle of humerus, via the common flexor origin. A tendinous hub that it shares with the five long forearm flexors; flexor carpi radialis, flexor carpi ulnaris, pronator teres, flexor digitorum superficialis and profundus.

The muscle has a relatively short inferior course, giving off a long tendon midway down the forearm. The tendon enters the palmar surface of the hand by passing superficially (i.e. external) to the flexor retinaculum. A few tendinous fibers blend with the superior surface of the retinaculum, while the majority widens and continues distally to finally insert into the palmar aponeurosis.

Nerve Supply of Hand Palmaris Longus Muscle

• The palmaris longus is supplied by the median nerve.^[rx]
• Palmaris longus is innervated by the median nerve (C7, C8), a branch from the medial and lateral cords of brachial plexus.

Function of Hand Palmaris Longus Muscle

Being located centrally in the anterior forearm, palmaris longus aids the flexor carpi ulnaris and  flexor carpi radialis muscles to perform a balanced flexion of the hand on the wrist. It also acts to stabilize the elbow joint when fully extended, as does the other forearm muscles that attach to the humerus and thus cross the elbow joint.

Fibers attaching to the palmar aponeurosis tighten this fascial sheath during the muscle’s contraction, resulting in a weak flexion of the 2nd to 5th metacarpophalangeal joints as the aponeurosis is being pulled towards the wrist. Tightening of the palmar aponeurosis also contributes to maintaining the hand’s grip while holding certain objects.