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INTRODUCTION
Cut out of locking head screws is the most common complication of locking plates in fracture fixation of the proximal humerus with potentially disastrous consequences. Aim of the study was to find the single best and combination of radiographic projections to reliably detect screw cut outs.

MATERIALS AND METHODS
The locking plate was fixed to six cadaveric proximal humeri. Six different radiographs were performed: anteriorposterior in internal (apIR), in neutral (ap0) and in 30° external rotation (apER); axial in 30° (ax30) and 60° (ax60) abduction and an outlet view. Each head screw (n=9) was sequentially exchanged to perforate the humeral head with the tip and all radiographs were repeated for each cut out. Randomized image reading by two blinded examiners for cut out was done for single projection and combinations.

RESULTS
Interrater agreement was 0.72-0.93. Best single projection was ax30 (sensitivity 76%) and the worst was the outlet view (sens. 17%). Standard combination of apIR/outlet reached a sens. of 54%. The best combination of two was: apER/ax30 (90% sens.), of three: apIR/apER/ax30 (96% sens.) and of four: apIR/ap0/apER/ax30 (100% sens.).

CONCLUSION
Standard radiographs (ap/outlet), especially in internal rotation, may miss nearly half of screw cut outs. Single best radiographic projection was an axial view with 30° abduction. To account for all cut outs and correct screw position a combination of four projections was needed. These simple and feasible intraoperative and postoperative radiographs help to detect screw perforations of the locking plate reliably.

LEVEL OF EVIDENCE
I (Study of Diagnostic Test).