A successful Total Knee Arthroplasty (TKA) requires stability, but rarely in primary TKA, a prosthesis with more constraint than a posterior-stabilizer (PS) is necessary. In patients with severe varus/valgus deformities with incompetent collateral ligaments or in knees that cannot be adequately balanced after ligaments release, a total-stabilizer (TS) prosthesis may be required. The purpose of our retrospective study is to evaluate clinical and radiographic outcomes at short mid-term follow-up in patients treated with a TS TKA. Between January 2013 and August 2016, 36 patients (38 knees) were treated with Stryker Triathlon TS cemented implants. Clinical and radiographic evaluation were performed preoperatively and postoperatively at 1 month, 3 months, 6 months, 1 year and at 1-year intervals thereafter. At final follow-up, 33 patients (35 knees) remained and were included in this study and followed with a mean follow-up of 26.6 months. Clinical evaluation was performed using the Western Ontario and McMaster Universities Arthritis Index (WOMAC score) and the Knee Society rating system that is subdivided into a knee score (KS) that rates only the knee joint itself and a functional score (FS). Knee Score (KS) and Functional Score (FS) increased significantly from a mean pre-operative value of 48 and 45, respectively, to a post-operative value at last follow-up of 86 and 82, respectively. Also WOMAC score improved significantly: the mean pre-operative WOMAC score was 45, while the mean post-operative WOMAC score, at last follow-up, was 19. The difference between pre- and post- operative results was significant at statistical analysis. In our opinion, when the adequately prosthesis balancing isn’t possible, because of primary or secondary severe varus/valgus deformity or severe soft tissues retraction, an available option is to perform a total knee arthroplasty with a total stabilizer polyethylene insert. TS prosthesis gives more stability during the most of ROM and, in addition, Triathlon system provides surgeons the possibility to choose a more constrained implant, than a standard PS one, during surgical procedure saving the bone stock. Our experience with this kind of prosthesis has provided good clinical and radiographic outcomes at a short mid-term follow-up with a low-rate of complications.