Palmaris Longus Muscle Variants

The palmaris longus muscle is one of the most variable muscles in the human musculoskeletal system. It arises from the flexor tendons at the medial humeral epicondyle and inserts into the palmar aponeurosis in the hand.

The muscle does not affect the function of the wrist and hand, likely because it has lost its purpose as humans began walking upright. Its major use these days is as a donor graft. However, it has been suggested that the palmaris longus tendon does play a role in carpal tunnel syndrome, since it increases intracarpal canal pressure on wrist extension and because there is a lower prevalence of palmaris longus agenesis in patients with carpal tunnel syndrome.

Absent Palmaris Longus Muscle

The most common variation is absence of the muscle. Clinically, there are multiple maneuvers that can be used to detect the presence of the tendon. The Schaeffer test was the first to be introduced: With the wrist flexed, the patient is asked to bring the thumb and small finger together. The palmaris longus tendon should be visible. Mishra's second test (he introduced two tests in his paper) can also be used: The thumb is abducted against resistance with the wrist in slight flexion, which should result in the visualization of the palmaris longus tendon.

In patients with median nerve palsy, who cannot abduct their thumbs, Mishra's first test can be used: There is passive hyperextension of the metacarpophalangeal joints followed by resisted active flexion at the wrist. The palmaris longus tendon should become visible.

Reversed Palmaris Longus Muscle

The normal appearance of the muscle is a short proximal belly and a long tendon. A reversed palmaris longus muscle may have a belly distally or along its mid section.

Accessory Palmaris Longus Muscle

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References

• Keese GR, Wongworawat MD, Frykman G. The clinical significance of the palmaris longus tendon in the pathophysiology of carpal tunnel syndrome. J Hand Surg Br. 2006; 31(6):657-60.
• Kose O, Adanir O, Cirpar M, Kurklu M, Komurcu M. The prevalence of absence of the palmaris longus: a study in Turkish population. Arch Orthop Trauma Surg. 2009; 129(5):609-11.
• Sebastin SJ, Lim AY. Clinical assessment of the palmaris longus-too many newer techniques? J Plast Reconstr Aesthet Surg. 2006; 59(7):784-6.