The increasing prevalence of proximal humerus fractures in the elderly population, particularly osteoporotic fractures, necessitates a biomechanical evaluation of Kirschner wire (K-wire) configurations used in percutaneous fixation. This study investigates the stability of different K-wire configurations and examines the effect of wire size and type (smooth vs. threaded). Using 27 synthetic humeri models, we compare three configurations as follows: four parallel ascending K-wires (box-type), two ascending and two descending K-wires, and a combination of both. Results show that adding descending K-wires significantly enhances stability, particularly against torsional forces. This study highlights the importance of wire type and configuration in stabilizing proximal humerus fractures. Multiplanar constructs with descending K-wires, especially threaded ones, offer better stability. These insights help improve surgical techniques for elderly and osteoporotic patients, but further research using cadaver models is needed for clinical validation.