The posterior tibial slope (PTS) is a key determinant of knee biomechanics, influencing anterior and posterior cruciate ligament (PCL) function, joint stability and load distribution. Abnormal PTS values predispose to instability and ligament reconstruction failures. This review aims to synthesize current evidence regarding the biomechanical, clinical, and surgical principles of PTS-modifying osteotomies, emphasizing their indications, techniques and outcomes. A comprehensive narrative review of the literature was conducted focusing on the definition, measurement methods, biomechanical implications, surgical approaches, and clinical results of PTS-reducing and PTS-increasing tibial osteotomies. Key data were extracted from biomechanical, radiologic, and clinical studies evaluating PTS correction and its effect on knee stability and success of ligamentous reconstruction. Measurement of PTS varies significantly among studies due to inconsistent radiological methods, i.e. radiograph versus magnetic resonance imaging or reference points and tibial axis definitions. PTS-reducing osteotomies effectively decrease anterior tibial translation, improving stability in ACL-deficient knees, while PTS-increasing procedures restore stability in PCL insufficiency and genu recurvatum deformities. Both techniques demonstrate substantial postoperative improvements in functional scores (Lysholm, IKDC, Tegner) with reported success rates up to 80–85%. Common complications include hinge fractures, patellar maltracking, and loss of correction, mitigated by accurate planning and fixation. PTS-modifying osteotomies represent valuable tools for managing ligamentous knee instability secondary to abnormal PTS. Optimal outcomes depend on precise radiologic assessment, appropriate surgical selection, and structured rehabilitation. Further longitudinal studies are warranted to determine their long-term effects on joint preservation and osteoarthritis progression.