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To examine the biomechanical behavior of 2 techniques of double-plate osteosynthesis for fractures of the adult distal humerus using conventional reconstruction plates and locking compression plates.Basic science study.Experimental in vitro study.Forty fresh-frozen human distal humeri specimens.Four matched groups with 10 humeri each, median age 74 years (46–95), were created using similar bone mineral density values. Two standard configurations of double-plate osteosynthesis (dorsal or 90° configuration) with either conventional reconstruction plates or locking compression plates were studied for biomechanical properties of the constructs. A fracture model with a 5-mm supracondylar osteotomy gap simulating metaphyseal comminution (AO type 13-A3.3) was used.Stiffness testing of the constructs in anterior/posterior bending, torsion, and axial compression loading. Evaluation of alterations of the bone–implant interface and failure patterns under cyclic loading and strength testing.The study demonstrates that primary stiffness in anterior/posterior bending and torsional loading is significantly increased by using locking compression plates in a 90° configuration (P < 0.05) as compared with dorsally applied plates. The differences between the different plate types are insignificant if applied in the same configuration. It is demonstrated that none of the tested implants failed under cyclic loading within the number of cycles expected for 3 months of use. The bone–implant interface is less likely to fail during strength testing with locking compression plates.The biomechanical behavior of the osteosynthesis depends more on plate configuration than plate type. Advantages of locking compression plates are only significant if compared with dorsal plate application techniques. Nevertheless, locking compression plates are helpful supplementary tools for achieving primary stable fracture fixation. This might be of considerable clinical relevance in patients with diminished bone mineral quality or in the presence of metaphyseal comminution.