Clinical outcomes of standard primary vs. primary rotating hinge total knee arthroplasty: a retrospective matched-pair analysis.

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.