Injury Mechanism of Acute Anterior Shoulder Dislocation Associated with Glenoid and Greater Tuberosity Fractures: A Study Based on Fracture Morphology.

Objective: Based on the morphological characteristics of glenoid and greater tuberosity (GT) fractures and the relationship between them, we explored the injury mechanism of acute anterior shoulder dislocation associated with glenoid and GT fractures.

Methods: From December 2013 to December 2019, we retrospectively reviewed the clinical data of patients who were diagnosed with acute anterior shoulder dislocation associated with glenoid and GT fractures in our hospital. According to the fracture site, a glenoid fracture group and a greater tuberosity fracture (GT) group were established, and the morphological characteristics of both glenoid and GT fractures were measured and statistically analyzed.

Results: A total of 41 patients (43 shoulders) met the inclusion criteria (39 unilateral shoulders and 2 bilateral shoulders). The mean age was 50.21 years (range, 22-71 years). A total of 27 shoulder injuries (62.8%) were split GT fractures and 33 shoulder injuries (76.7%) were combined with rotator cuff tears. The mean size of glenoid fragments was 30.16% and the mean displacement was 8.85 mm. The mean size of GT fragments was 28.43 mm. The mean superoinferior and anteroposterior displacements of the GT fragment were 6.77 mm and 4.96 mm, respectively. There was a negative correlation between the size of glenoid and GT fracture fragments (r = -0.64, P < 0.05). The glenoid fragments in the Ideberg type Ia glenoid fracture group were smaller than those in the Ideberg type II glenoid fracture group (28.41% and 40.95%, respectively), while the size of GT fragments in the type Ia group were larger than those in the type II group (29.77 mm and 20.21 mm, respectively) (P < 0.05). The GT fragments in the split GT fracture group were larger than those in the avulsion or depression GT fracture group (33.69 mm, 19.07 mm and 21.12 mm, respectively), while the size of glenoid fragments in the split GT fracture group were smaller than those in the avulsion or depression GT fracture group (23.57%, 41.37%, and 43.42%, respectively) (P < 0.05). As for the displacement direction of GT fragments, depression fractures were mainly inferior displacements, avulsion fractures were mainly anterosuperior displacements, while split fractures were mainly posteroinferior displacements (P < 0.05). Multiple regression analysis suggested that the type and the fragment size of GT fractures have a significant influence on the size of glenoid fragments.

Conclusion: Acute anterior shoulder dislocations associated with glenoid and GT fractures are often combined with rotator cuff tears. There is a negative correlation between the size of glenoid and GT fragments, and split GT fractures are most common. Such injuries are highly correlated to the relative spatial location between the GT and the glenoid when the shoulder dislocates.