Abstract
BACKGROUND: In complex primary cases- marked by significant ligamentous instability, extensive bone loss, or severe deformities- standard total knee arthroplasty (TKA) may be insufficient. Rotating-hinge (RH) TKA offers a higher-constraint alternative. We retrospectively compared the clinical outcomes of primary RH TKA with those of standard primary (SP) TKA. METHODS: Nineteen patients per group were matched for age, sex, and follow-up (SP: 68.8 ± 6.8 years; RH: 68.2 ± 8.1 years; 11 females each). Patients with < 2 years of follow-up were excluded. Outcomes included stability, range of motion (ROM), radiographic loosening, leg alignment, and the following scores: Hospital for Special Surgery (HSS), Knee Society Score (KSS), Oxford Knee Score (OKS), EuroQol-5 Dimension-3 Level (EQ-5D-3 L), and Visual Analogue Scale (VAS). RESULTS: At follow-up (SP: 34 ± 7 months; RH: 32 ± 6 months, p = 0.346), medio-lateral instability was present in 26% of SP knees and absent in RH knees (p = 0.023). RH TKA had higher ROM by a mean 9° (126 ± 12° vs. 117 ± 9°; mean Δ = 9°, 95% CI 1.7-16.3°, Cohen d = 0.86; p = 0.012). No cases of antero-posterior instability, radiographic loosening, or axis malalignment occurred. Group differences were non-significant for HSS (89 ± 8 vs. 87 ± 19, p = 0.564), KSS (85 ± 14 vs. 87 ± 26, p = 0.790), OKS (17 ± 7 vs. 22 ± 11, p = 0.118), EQ-5D-3 L index (0.694 ± 0.314 vs. 0.781 ± 0.265, p = 0.364), and VAS (78 ± 27 vs. 77 ± 17, p = 0.886). CONCLUSION: Primary RH TKA is a viable alternative to standard TKA in selected cases, demonstrating significantly less medio-lateral instability (0% in RH vs. 26% in SP, p = 0.023) and greater range of motion (126 ± 12° in RH vs. 117 ± 9° in SP, p = 0.012) in this cohort.