Abstract
BACKGROUND: Endoprosthetic knee replacement using megaprostheses has become a common strategy for preserving joint function in patients with distal femur tumors. While existing literature has primarily focused on surgical techniques, complications, and implants, recent improvements in patient survival rates have sparked increased interest in the long-term functional outcomes associated with this treatment. METHODS: This case-control study evaluated functional outcomes-Timed Up and Go (TUG), 6-Minute Walk Test (6MWT), knee flexor and extensor muscle strength, and sagittal knee range of motion-and health-related quality of life (SF-36) between patients with distal femoral megaprostheses (n = 31) and healthy controls (n = 48). Participants performed the TUG and 6MWT equipped with an inertial measurement unit. Additionally, bivariate Spearman correlations were calculated within the patient group to assess relationships between Musculoskeletal Tumour Society (MSTS) scores and functional outcomes. RESULTS: Patients performed significantly worse than controls in the TUG test, with longer completion times (Mean Difference: -3.3 s; 95% CI: -5.7 to -0.9; p = 0.008), reduced rotational speed during the middle turn (Mean Difference: 16°/s; 95% CI: 7 to 25; p < 0.001) and final turn (Mean Difference: 22°/s; 95% CI: 9 to 34; p < 0.001), and lower vertical acceleration during the Sit-to-Stand phase (Mean Difference: 1.3 m/s²; 95% CI: 0.1 to 2.5; p = 0.032). In the 6MWT, patients walked 86 m less on average than controls (95% CI: 35 to 136; p = 0.002). Knee range of motion was significantly reduced, with median flexion of 90.2° (range: 5-125) in patients versus 136.4° (range: 115-150) in controls (p < 0.001, Z = -7.268). Muscle strength was also markedly lower in patients (p < 0.001). The SF-36 revealed significant differences in the Physical Component Summary (Mean Difference 95% CI: 15.5 [10.0 to 20.9]; p < 0.001), while no significant differences were found in the Mental Component Summary (p > 0.05). In patient group, bivariate Spearman correlations indicated a very strong positive association between MSTS scores and knee extension strength (ρ = 0.710; p < 0.001), and strong positive correlations with sagittal knee range of motion (ρ = 0.472; p = 0.015), total walking distance in 6MWT (ρ = 0.474; p = 0.019), and final turn rotational speed in TUG (ρ = 0.439; p = 0.032). CONCLUSION: Our findings demonstrate a strong association between knee extensor strength and range of motion with overall functional performance, as reflected in MSTS scores. While nearly 75% of patients achieved scores classified as "good" to "excellent," objective measures from the TUG and 6MWT revealed significant performance deficits compared to healthy controls, likely due to limitations in knee extensor strength and range of motion. These results highlight the need for targeted rehabilitation strategies focused on enhancing muscle strength and range of motion to optimize long-term functional recovery in these patients.