In the shoulder joint, lesser tuberosity avulsion fracture is a rare injury and consists of about 2% of proximal humerus fractures¹. The first case report of an isolated lesser tuberosity avulsion fracture was published in 1985². Lesser tuberosity avulsion injuries in adolescents are even more uncommon but it was reported that those injuries have gradually increased in the recent literature³. With increased participation in athletic activity in younger patients, accidents and traumas have grown, especially at that age⁴.

The injury mechanism is acute forced shoulder joint external rotation with the abduction of arm, which has been reported in younger patients who are enjoying sports such as football, hockey, volleyball, wrestling, and skateboarding⁵. The avulsion injury occurs by sudden traction force on the lesser tuberosity caused by counter contraction of the subscapularis muscle to oppose the external rotation movement of the shoulder joint⁶. During adolescence, traumas in the subscapularis muscle lead more often to osseous avulsion of the lesser tuberosity or subscapularis tendon, as opposed to often to intrasubstance tendinous injury in adults⁷.

For acute and displaced injuries, treatment seems not debatable and results of surgical repair appear good. However, because of the variability of the mechanism and presentation of these injuries, the diagnosis is often missed initially⁸. Diagnosis of this injury is often challenging, leading to delays in treatment. Missing to diagnose these injuries may lead to nonunion of bony structures and eventually lead to chronic shoulder pain and muscle weakness⁹.

In this paper, we report the case of a 14-year-old boy who complained of persistent shoulder pain and muscle weakness after an injury 8 months ago.

This report was approved by the Institutional Review Board of Soonchunhyang University Bucheon Hospital (No. 2024-02-022). Written informed consent was obtained from the patient for the publication of this report including all clinical images.

The case of isolated fracture of the lesser tuberosity of the proximal humerus in children or adolescents is very rare worldwide. In Korea, Yum et al.¹⁰ reported one case. Compared to previous cases of lesser tuberosity avulsion fracture of the humerus in an adolescent, this patient had a much larger and displaced bony fragment. This injury is hard to diagnose early and about half of cases are presented as chronic shoulder joint pain. Missing early diagnosis of this could cause later clinical disorders.

The injury mechanism is as follows: avulsion of subscapularis when acute external rotation force was applied with proximal humerus externally rotated⁶. Diagnosis of isolated avulsion fracture of lesser tuberosity without dislocation of shoulder joint preferentially needs identification of injury mechanism. In addition, for patients complaining of shoulder pain, if there is no improvement in symptoms after sustained conservative treatment after injury, the disease should be suspected. Those patients may show mild anterior shoulder joint tenderness or mild limit of internal rotation of the shoulder joint². In that case, a close review of a simple X-ray could be helpful, as specific appearance shows that contracted infraspinatus draws an avulsed bone fragment from infraspinatus’ insertion site to subarticular space^11,12. Additional evaluation tools such as computed tomography (CT) and MRI can be considered. CT can accurately show bony defect area, degree of displacement of bony fragment, size of bone fragment, and fracture type. MRI is a helpful study showing the status of nearby soft tissue like infraspinatus and bone fragments, and soft tissue injury such as a tear of biceps brachii or glenoid labrum. After plain radiographs and magnetic resonance arthrography were performed, CT was not performed because we thought that sufficient data were obtained.

Standard surgical indication of humeral lesser tuberosity fracture is displaced fracture (fracture gap is more than 5 mm, fracture angulation is bigger than 45°), mechanical motion difficulty, failure of conservative treatment, and severe accompanied injury. But Ogawa and Takahashi⁶ conclude conservative treatment can obtain satisfying results in acute, nondisplaced humeral lesser tuberosity fracture, but regardless of size or displacement of a bony fragment, surgical treatment shows superior results. In complex comminuted fractures, by drilling a hole in the proximal humerus and then anchoring absorbable or nonabsorbable suture, fixation can be achieved causing minimal damage on the lesser tuberosity. After then fixation power can be increased by a screw with suture, in case of large size bone fragment fixation can be achieved by cortical screw^13,14. However, usage of this screw can cause physeal injury to humeral lesser tuberosity and early closure of the growth plate; therefore, it should be implemented carefully.

We decided on surgical treatment considering clinical symptoms and MRI findings which show a complete rupture of the infraspinatus tendon and about 55×13-mm size irregular shape bony defect. Despite the possibility of physeal injury to firmly fix a large bone defect, the authors used a cannulated screw to humeral lesser tuberosity and repaired the infraspinatus additionally.

This study has several limitations. This patient was followed up for only 6 months. Later, continuous follow-up is needed about physeal injury and clinical course. Since this is a rare case, this paper consists of only one case. In the future, it is thought that systematic review will be needed by studying more cases at multiple institutions.

In adolescents, isolated avulsion fracture of humeral lesser tuberosity is far rare. This injury is hard to diagnose early and sometimes can appear as chronic shoulder joint pain. Missing early diagnosis of this injury case can cause important clinical disorders later. So early diagnosis and treatment open reduction and internal fixation to isolate fracture of the lesser tuberosity of the proximal humerus in adolescents if needed.