An anomalous muscle predisposing to the development of hypothenar hammer syndrome

The hypothenar hammer syndrome describes a thrombosis of the ulnar artery caused by recurrent trauma to the hand. It is the most common form of posttraumatic occlusive diseases of the upper extremity. In this case report, an anomalous muscle was identified as a contributing cause to the condition in combination with recurrent trauma. We describe the history, treatment options, and outcome of this rare event and review the literature regarding anatomical variations of the forearm and wrist. In summary, we believe that our patient had compression of the ulnar artery caused by the anomalous muscle and subsequently developed arterial thrombosis that was further exacerbated by his occupational trauma and his smoking habit.