Unilateral absence of the thoracic part of the trapezius muscle.

The absence of some muscles, such as pectoralis major, serratus anterior and quadratus femoris have been described, however the absence of trapezius, either in isolation or in association with other structures, is not often observed. In this case study, we present a case of partial absence of the left trapezius muscle in an adult black male cadaver, which had a large aponeurosis replacing the ascending fibres and some of the transverse fibres of the muscle. Histological analysis showed the presence of a few muscle fibres in the aponeurosis. From a functional viewpoint, it is possible that this individual would have had difficulty in moving his shoulder, especially during flexion, abduction and circumduction of the arm.