Traumatic bone fractures are often debilitating injuries that may require surgical fixation to ensure sufficient healing. Currently, the most frequently used osteosynthesis materials are metal-based; however, in certain cases, such as complex comminuted osteoporotic fractures, they may not provide the best solution due to their rigid and non-customizable nature. In phalanx fractures in particular, metal plates have been shown to induce joint stiffness and soft tissue adhesions. A new osteosynthesis method using a light curable polymer composite has been developed. This method has demonstrated itself to be a versatile solution that can be shaped by surgeons in situ and has been shown to induce no soft tissue adhesions. In this study, the biomechanical performance of AdhFix was compared to conventional metal plates. The osteosyntheses were tested in seven different groups with varying loading modality (bending and torsion), osteotomy gap size, and fixation type and size in a sheep phalanx model. AdhFix demonstrated statistically higher stiffnesses in torsion (64.64 ± 9.27 and 114.08 ± 20.98 Nmm/° vs. 33.88 ± 3.10 Nmm/°) and in reduced fractures in bending (13.70 ± 2.75 Nm/mm vs. 8.69 ± 1.16 Nmm/°), while the metal plates were stiffer in unreduced fractures (7.44 ± 1.75 Nm/mm vs. 2.70 ± 0.72 Nmm/°). The metal plates withstood equivalent or significantly higher torques in torsion (534.28 ± 25.74 Nmm vs. 614.10 ± 118.44 and 414.82 ± 70.98 Nmm) and significantly higher bending moments (19.51 ± 2.24 and 22.72 ± 2.68 Nm vs. 5.38 ± 0.73 and 1.22 ± 0.30 Nm). This study illustrated that the AdhFix platform is a viable, customizable solution that is comparable to the mechanical properties of traditional metal plates within the range of physiological loading values reported in literature.