Background <p>Pediatric femoral neck fractures require stable fixation to avoid complications. It remains unclear whether fixation with the Proximal Humeral Internal Locking System (PHILOS) can serve as an alternative to cannulated screw fixation. The purpose of this study was to compare the biomechanical properties of PHILOS and cannulated screws for stabilizing unstable pediatric femoral neck fractures using a synthetic bone model.</p> Materials and methods <p>Twelve fourth-generation synthetic composite femurs were randomly assigned to screw fixation (Group S) or PHILOS fixation (Group P) (<i>n</i> = 6 each). A standardized vertically oriented Delbet type II osteotomy was created in all specimens. Group S was fixed with three 6.5-mm cannulated screws, whereas Group P received a PHILOS plate with 3.5-mm locking screws. Each specimen underwent a standardized loading protocol using a universal testing machine. Axial stiffness, cyclic displacement, ultimate failure load, and failure modes were recorded and statistically compared between groups.</p> Results <p>No statistically significant difference was found in axial stiffness between Group P (746 ± 300&#xa0;N/mm) and Group S (753 ± 256&#xa0;N/mm) (<i>p</i> = 1.000). Displacement after cyclic loading was significantly greater in Group P (1.42 ± 0.3&#xa0;mm) compared with Group S (0.57 ± 0.2&#xa0;mm) (<i>p</i> = 0.004). The ultimate failure load was higher in Group S (2378 ± 513&#xa0;N) than it was in Group P (1652 ± 206&#xa0;N) (<i>p</i> = 0.025). Upon reaching ultimate load, all specimens in both groups failed at the femoral head region due to femoral head broken.</p> Conclusions <p>The adult PHILOS plate with 3.5-mm locking screws demonstrated inferior biomechanical stability compared with three 6.5-mm cannulated screws in this synthetic composite femur model.</p> Level of evidence <p>Controlled laboratory study.</p>