PemAvascular necrosis (AVN) of the humeral head worsens the outcomes of treatment of proximal humeral fractures. This study aimed to evaluate the frequency of AVN in patients with three- and four-part fractures of the proximal humerus and to improve treatment outcomes using a new reduction technique. By design, this work was a retrospective–prospective cohort study. We recruited 357 patients with three- and four-part fractures of the proximal humerus. In the main group, 200 patients (147 women [73.5%] and 53 men [26.5%]) underwent surgery with a condylus–plate system (RF patent No. 2705234). In the comparison group, 157 patients (120 women [76.4%] and 37 men [23.6%]) had surgery that relied on conventional techniques. At two years, 329 patients were available for follow-up. The designed reduction technique reduced the incidence of Cruess stage II–IV AVN from 28.8% to 17.3% (p = 0.015). The risk of AVN increased with age, diabetes mellitus, osteoporosis, and multimorbidity.