The use of osseointegrated implants as a solution for amputation treatment, providing a stable connection between the stump and prosthetic limb, is expanding its application to different anatomical districts. A particular focus is put on upper limb amputations, where socket-suspended systems often lead to high abandonment rates of prostheses and osseointegrated implants can enhance prosthetic-limb use, and improve bone perception and range of motion, leading to a better quality of life. This study aims to evaluate the effect of bone-implant interference and implant length of a straight implant, on the primary stability of a humerus CAD model through finite element analysis. The results suggest that a compromise can be made between interference and length to accommodate varying bone morphology and stump length. Additionally, the study results may suggest re-evaluating the prescribed weight limits for transhumeral implants based on their actual load-bearing capacity. Comparison with existing literature underscores the relevance of the study's optimizing design parameters for improved clinical outcomes.