Reconstructive Arthroplasty for Malignant Bone Tumors of the Knee—A Single-Center Experience of Functionality and Quality of Life

<b>Background/Objectives:</b> Resection arthroplasty is well established in treating bone defects following tumor resection, with the distal femur and proximal tibia being its most common localizations. The aim of this study was to analyze the functional outcomes and quality of life following endoprosthetic reconstruction for malignant bone tumors of the knee joint. <b>Methods:</b> We retrospectively included all patients treated with an endoprosthetic reconstruction following resection of a malignant bone tumor of the knee at our institution. Functional outcomes (KOOS, OKS, MSTS, and KSS) and health-related quality of life scores [QoL] (SF-36, Karnofsky Index) were evaluated. Chi-square and Fisher's exact test was used for categorical variables, T-test and Whitney U-Mann tests for continuous variables. Survival was calculated using the Kaplan-Meier curves. <b>Results:</b> 32 patients were included. A total of 12 patients had died at the time of follow-up. Among the remaining 20 patients (m:w 17:3), mean follow-up was 8.1 years (range, 8.12 ± 6.8). Mean age at the time of tumor diagnosis was 50 ± 23.3 (10-83) years. According to age, patients were divided into two groups (group C1: <29 years, group C2: >29 years). Group C1 showed significantly better results regarding functional outcome (<i>p</i> < 0.05). The anatomic location of the replacement and a revision surgery did not influence the functional outcome (<i>p</i> > 0.05). QoL showed no significant differences in subgroup analysis (<i>p</i> > 0.05). Primary bone tumors had a significantly better survival (primary tumor: 216.90 months [168.42-265.83]; secondary tumor: 37.03 months [11.71-62.35] <i>p</i> = 0.01). Furthermore, pathologic fractures were associated with significantly worse survival (pathologic fracture: 50.24 months [0.00-102.43]; pathologic fracture 190.63 moths [139.28-241.45]; <i>p</i> = 0.007). <b>Conclusions:</b> Knee resection arthroplasty can offer meaningful long-term functional outcomes and acceptable quality of life in selected patients with musculoskeletal tumors. While the rarity and heterogeneity of such cases remain a challenge, our findings contribute to the growing evidence supporting this complex but limb-sparing surgical option.