Three-headed reversed palmaris longus muscle and its clinical significance

The palmaris longus muscle originates from the medial epicondyle of the humerus. After a short distance, almost in the middle of the forearm, the muscle belly is toggled into a broad tendon which is inserted into the flexor retinaculum and the palmar aponeurosis. After dissection of the left forearm of a 73-year-old female cadaver we found a reversed palmaris longus muscle. This means that the palmaris longus muscle was tendinous in its upper part and muscular in its lower part. Additionally, the muscle belly was triple, thus our finding was characterized as "three-headed reversed palmaris longus muscle". Rarely is the palmaris longus muscle double, whereas the three-headed reversed palmaris longus muscle is mentioned only once in the literature as a surgical finding, in a patient who suffered from edema and pain in the wrist [Yildiz, M., Sener, M., Aynaci, O., 2000. Three-headed reversed palmaris longus muscle: a case report and review of the literature. Surg. Radiol. Anat. 22, 217-219]. The overuse of the reversed palmaris longus muscle can lead to the muscle's local hypertrophy. According to the literature a reversed palmaris longus muscle may cause a compartment syndrome with pain and edema in the wrist's area, the carpal tunnel syndrome and Guyon's syndrome. The described variation is also useful to the hand surgeon, as the palmaris longus muscle is an anatomical landmark for operations at this area.