Background <p>Proximal humerus fractures (PHFs) are fragility fractures that commonly occur in elderly patients and are frequently associated with osteoporosis. Despite the widespread use of locking plate fixation for displaced fractures, complication and reoperation rates remain high, particularly in complex three- and four-part fracture patterns. Although increasing screw density improves fixation stability, the relative significance between screw number and screw position (particularly medial column support) remains unclear. This study aims to determine whether fixation failure is driven by screw density or by the quality of medial column support and fracture biology in osteoporotic PHFs.</p> Methods <p>This retrospective cohort study included elderly patients (≥ 65 years) with confirmed osteoporosis who underwent locking plate fixation for three- or four-part PHFs between January 2018 and December 2023 with a minimum radiological follow-up of 24 months and subsequently required revision surgery due to radiological failure. The patients were classified based on screw density (low vs. high), and the distribution of mechanical and biological causes of revision was analyzed. In a second analysis, patients who underwent revision surgery were compared with those who did not to examine the relationship between medial support quality (defined by inferomedial and calcar screw placement) and the likelihood of revision.</p> Results <p>A total of 24 patients who required revision surgery were included in the primary analysis (15 with low and nine with high screw density). The distribution of revisions for mechanical and biological reasons did not differ between the groups (<i>p</i> &gt; 0.05). In a secondary analysis involving 166 patients (24 revision, 142 non-revision), limited medial support (one inferomedial/calcar screw) was significantly more common among revision cases than non-revision cases (37.5% vs. 4.9%), whereas adequate medial support (≥ 2 inferomedial/calcar screws) predominated in patients without revision (95.1%) (<i>p</i> &lt; 0.001).</p> Conclusion <p>In osteoporotic PHFs requiring surgical fixation, revision risk is not determined by the total number of screws but by the quality of medial column support. Adequate inferomedial and calcar screw placement was strongly associated with a lower revision rate, emphasizing that targeted screw positioning rather than increased screw density is the critical determinant of fixation durability in osteoporotic bones.</p> Level of Evidence III <p>Retrospective cohort study.</p>