Three in one - unusual palmaris longus muscle anatomical variation

The palmaris longus muscle (PLM) is one of the most variable muscles in human body, presenting a wide range of morphological variants such as reversed course, biventer muscle, bifurcated tendon, or total agenesis. Their clinical impact is particularly important in the diagnosis and treatment of carpal tunnel syndrome and reconstructive surgery. We present a case of PLM including a previously undescribed combination of variations. A routine dissection of male cadaver aged approximately 60 years demonstrated a biventer muscle, with superior and inferior belly being interrupted by a long tendon. The inferior belly passed deep to the flexor retinaculum and its terminal tendon connected to the flexor digitorum superficialis tendon of the fifth finger. The clinical importance of variations found have been described separately, including unsuitability of biventer muscles for tendon reconstruction and increased risk for developing carpal tunnel syndrome in patients with a PLM tendon passing deep to the flexor retinaculum. In conclusion, as another variation of PLM is described, it is crucial to bear in mind the potential morphological types of the muscle in the diagnosis and treatment of patients, especially in surgery of the hand and forearm.