**2. Materials and Methods**

Patients with humeral head fractures diagnosed in our trauma department between 2008 and 2018 were identified. Patients with computed tomography (CT) scans of the affected shoulder were included. CT scans with low image quality or missing medial slices to assess the rotator cuff were excluded. All fractures were categorized according to Neer's classification system (Table 1) [1]. Two- and Three-Part fractures, as well as fracturedislocations and head-split fractures, were also excluded in order to generate a homogenous study population of four-Part fractures without fracture-dislocation (Figure 1). The study has been approved by the Ethics Committee at the University of Regensburg (20-1848-104).


**Table 1.** Schematic overview of Neer's modified classification system [1].

I: minimal dislocation, under 1 cm and less angulation than 45◦.

**Figure 1.** Flowchart of case inclusion/exclusion. The study population consists only of four-Part fractures of the humeral head.
