Metal plates are commonly used for the fixation of metacarpal fractures, but are associated with complications such as tendon adhesions that impair finger mobility. AdhFix, a novel osteosynthesis material, may reduce these complications, but its biomechanical performance in the metacarpal region remains untested. This study aimed to evaluate internal bending moments during postoperative rehabilitation and assess the biomechanical potential of AdhFix in treating comminuted metacarpal shaft fractures using a human cadaveric model. In five cadaveric hands, unstable shaft fractures of the second, third, and fourth metacarpals were simulated using a 3 mm osteotomy gap and stabilized with polyether ether ketone (PEEK) plates and stainless-steel cortical screws. A custom 3D-printed guide ensured accurate osteotomy and screw positioning. Tendon loading was simulated by pulling flexor digitorum profundus tendons until fingertip-to-palm contact was achieved, followed by wrist flexion using 100 N of force on the flexor carpi radialis and ulnaris tendons. Bending of the fixation was captured using stereographic imaging, and internal bending moments were calculated via finite element modeling. After removal of the PEEK plate, the procedure was repeated using AdhFix for fixation. Maximum internal bending moments were 6.14 ± 2.03 Nmm during finger flexion and 3.37 ± 1.64 Nmm during wrist flexion. AdhFix demonstrated mechanical integrity under both conditions with no observed failure. Statement of Clinical Significance: AdhFix may provide a mechanically stable alternative to conventional plates during early rehabilitation, potentially reducing tendon adhesions and preserving finger mobility.