Isolated avulsion fracture of the lesser tuberosity represents an extremely rare injury that occurs mainly in younger patients. This report outlines the case of a 35-year-old healthy man who sustained a bony avulsion of the subscapularis tendon during an abduction external rotation trauma to his left shoulder. The injury was diagnosed by physical examination, standard radiographs, and magnetic resonance imaging. An arthroscopic reconstruction including closed reduction and internal fixation using suture anchors was performed. After a follow-up of 6 months, the patient's Constant Score increased from 62.4 points preoperatively to 91.3 points. At the latest follow-up, the patient was completely pain free, had regained a full work activity level, and returned to overhead sports. On postoperative standard radiographs and magnetic resonance images, the bony fragment was shown to be consolidated in an anatomic position. In cases of displaced isolated fractures of the lesser tuberosity without significant subluxation or dislocation of the long head of the biceps arthroscopic reconstruction using suture anchors can lead to a good clinical and radiological result.