False aneurysm of a proper digital artery caused by repetitive microtrauma in a 16-year-old baseball player.

We report a case of false aneurysm of a proper digital artery of the thumb in a 16-year-old baseball player. Resection of the aneurysm and end-to-end anastomosis resulted in relief of the patient's symptoms and recovery allowing a return to baseball activity. Repetitive microtrauma, which is an atypical cause of a false aneurysm, to the ulnar aspect of the left thumb caused by swinging a bat led to formation of the false aneurysm. Although the occurrence of an aneurysm related to a sports activity is rare, surgeons should consider aneurysm as a possible diagnosis in a case with mass formation of the hand related to sports activity.