The Palmaris Longus is a slender, spindle-shaped muscle located in the superficial layer of the anterior forearm, notable for its long, cord-like tendon. This structure begins near the elbow and extends down to the wrist, where its tendon is often visible just beneath the skin. While it is classified as a flexor muscle, its contribution to wrist movement is minimal, making it one of the most variable muscles in the human body. The tendon’s frequent absence in a portion of the population has captured the interest of researchers and clinicians.
Identifying the Palmaris Longus
The Palmaris Longus muscle originates from the medial epicondyle of the humerus, sharing a common point of origin with several other forearm flexors. Its long, flat tendon crosses the wrist and inserts into the palmar aponeurosis and the flexor retinaculum, layers of deep fascia in the palm of the hand. The primary function of the muscle is to produce weak flexion at the wrist joint. It also contributes to the stability of the palmar skin by tensing the palmar aponeurosis, which can help in gripping actions.
You can easily check for the presence of this tendon using a simple test. First, touch the tip of your thumb to the tip of your pinky finger to form a circle. Next, slightly flex your wrist, lifting your hand upward from a flat surface. If the tendon is present, a thin, raised cord should become visible in the center of your inner wrist, positioned between the two more prominent tendons on either side. If no tendon appears, the Palmaris Longus is likely absent in that forearm, which is a normal variation.
Prevalence of Absence and Vestigial Status
The absence of the Palmaris Longus tendon is a well-documented anatomical phenomenon, with its prevalence varying widely across global populations. Standard anatomy texts often cite its absence in approximately 15% of individuals, though this figure is highly dependent on ethnicity. Studies have shown a lower rate of absence in certain Asian and Black populations (sometimes as low as 1.5% to 4.8%), while some Caucasian and Turkish populations exhibit higher rates (sometimes exceeding 20%). The absence can be unilateral (missing in only one arm) or bilateral (missing in both arms).
This muscle is frequently cited as a vestigial structure, a remnant of evolution that has lost its original function over time. In primate ancestors, a fully developed Palmaris Longus muscle likely played a more significant role in grasping and hanging. For modern humans, its minimal contribution to wrist flexion means its absence causes no discernible functional deficit. Clinical research confirms that individuals without the tendon maintain the same level of grip strength and overall forearm function as those who have it.
Essential Role as a Donor Graft
Despite being functionally dispensable, the Palmaris Longus tendon holds considerable value in the clinical setting. It is highly prized by surgeons as the most popular choice for an autograft—a segment of tissue taken from one part of a patient’s body and used to repair another. Its superficial location and long length make it easily accessible for harvest with minimal invasion. Crucially, its removal does not impair the function of the hand or forearm.
The harvested tendon is used in various reconstructive surgeries, primarily to repair damaged tendons and ligaments elsewhere in the body. Common procedures include reconstruction of torn ligaments in the wrist and the repair of long flexor tendons in the fingers. Surgeons also use the Palmaris Longus for ligament reconstruction around the elbow, such as in ulnar collateral ligament repair, a procedure often associated with overhead-throwing athletes. Although it is the preferred donor, a small percentage of harvested tendons may not be long or thick enough for a specific graft requirement, necessitating the selection of an alternative donor site.