Background and purpose There is considerable uncertainty about the optimal treatment of displaced 4-part fractures of the proximal humerus. Within the last decade, locking plate technology has been considered a breakthrough in the treatment of these complex injuries. Methods We systematically identified and reviewed clinical studies on the benefits and harms after osteosynthesis with locking plates in displaced 4-part fractures. Results We included 14 studies with 374 four-part fractures. There were 10 case series, 3 retrospective observational comparative studies, 1 prospective observational comparative study, and no randomized trials. Small studies with a high risk of bias precluded reliable estimates of functional outcome. High rates of complications (1664%) and reoperations (1127%) were reported. Interpretation The empirical foundation for the value of locking plates in displaced 4-part fractures of the proximal humerus is weak. We emphasize the need for well-conducted randomized trials and observational studies.