Study on Bilateral Reversed Palmaris Longus Muscle with Trifid Insertion: A Rare Variation

Normally, the palmaris longus muscle arises from the humerus's medial epicondyle via a common flexor origin. The muscle belly forms a tendon in the middle of the forearm that inserts into the flexor retinaculum and the palmar aponeurosis. Objective of this study is to present rare variation of Palmaris Longus muscle. In our study, we discovered a reversed palmaris longus muscle after dissecting both forearms of a 45-year-old male cadaver. This indicates that the palmaris longus muscle was tendinous in its proximal portion and muscular in its distal portion. The fleshy belly of muscle was unsheathed by separate fascia as it passed over the flexor retinaculum. The muscle belly spread on both sides of each palm for trifid insertion, which was centrally into palmar aponeurosis, laterally continuous with the fascia covering the thenar muscles, and medially with Abductor digit minimi. It had tendinous connections with the muscle mass on both sides. A surgical finding in a patient with edema and wrist pain was a bilateral reversed palmaris longus muscle, as mentioned in the literature. Overuse of the reversed palmaris longus muscle can result in local hypertrophy. According to the literature, a reversed palmaris longus muscle can result in a compartment syndrome with pain and edema in the wrist, carpal tunnel syndrome, and Guyon's syndrome. The variation is also beneficial to hand surgeons because the palmaris longus muscle serves as an anatomical landmark for operations in this area.