Patient-Specific Restoration of Constitutional Alignment Within Predefined Safety Boundaries Using Three-Dimensional Navigation in Primary Total Knee Arthroplasty: One-Year Clinical and Radiographic Outcomes

<b>Background/Objectives</b>: This study investigates a surgical concept that restores constitutional bony alignment within predefined safety boundaries in primary total knee arthroplasty (TKA) using modern 3D navigation. The technique combines a standard knee implant with advanced navigation technology to achieve patient-specific alignment and recreate native joint mechanics. One-year outcome was evaluated to assess first clinical results. <b>Methods</b>: In this retrospective study, a consecutive series of 185 TKAs (171 patients) was analyzed. All patients underwent patient-specific restoration of constitutional alignment within predefined safety boundaries using a 3D navigation system and a standard knee arthroplasty implant. The clinical outcomes were assessed using the 2011 Knee Society Score (KSS), the Forgotten Joint Score (FJS-12), the UCLA Activity Scale, and a five-step Likert scale to evaluate satisfaction. <b>Results</b>: In a total of 87.6% of cases, the patients reported being either satisfied or very satisfied with their TKA. No patients reported strong dissatisfaction. The KSS demonstrated significant improvements in all subcategories (all <i>p</i> < 0.001). The FJS-12 increased significantly from a preoperative average of 32.5 points to 79.3 points postoperatively (<i>p</i> < 0.001). The mean UCLA activity score rose from 4.9 preoperatively to 6.6 postoperatively (<i>p</i> < 0.001). In 97.7% and 90.2% of cases, the femoral mechanical angle (FMA) and tibial mechanical angle (TMA) bone cuts were within ± 1° of the planned angles. A strong correlation was observed between the planned and verified bone cuts for the FMA (ρ = 0.939) and the TMA (ρ = 0.875). <b>Conclusions</b>: Patient-specific restoration of constitutional alignment within predefined safety boundaries in primary TKA using modern 3D navigation is a promising strategy for personalized joint reconstruction using a standard knee arthroplasty implant. It combines precision and reproducibility with high patient satisfaction by respecting each patient's constitutional alignment.