This research explores the possibility of redesigning a surgical guide with the aim of improving the overall accuracy of the surgery and reducing the time of the procedure. The paper proposes a study of functional analysis (FA) focused on the particularities of custom-fitting products fabricated via Selective Laser Melting (SLM). The authors approach each stage of existence in the product’s life cycle with technical FA in order to obtain a custom-fitting surgical guide that better satisfies the customer’s needs and yet permit a sustainable manufacturing process. The FA study is targeted on the specific characteristics of SLM of single part products and uses tools such as FAST diagrams, product life cycle analysis, technical and economic matrices. The merging of SLM technology with technical FA led to a number of modifications in the functionality of the surgical guide, and has been described by the originating surgeons as a positive improvement.