A three-headed psoas major muscle: a case report.

BACKGROUND Multiple anatomical variations, from anomalous courses to additional structures, have been reported in muscles from different compartments of the human body. We report an extremely rare case of a psoas major muscle presenting as a three-headed structure with variable morphology. MATERIALS AND METHODS During a routine dissection of the posterior abdominal wall of a 82-year-old male cadaver, an anomalous PM muscle with supernumerary head was identified, photographed and subjected to further measurement. RESULTS Although the anatomy of the dissected posterior abdominal wall structures was typical, a three-headed psoas major muscle composed of superficial, intermediate and deep heads was identified. CONCLUSIONS It is important to be aware of morphological variability of muscles, especially those considered to be constant, since an anomalous structure might interfere not only with their functions, but also lead to further clinical consequences.