Objective arthrometric assessment of sagittal stability after total knee arthroplasty

Aims To assess sagittal stability in vivo using an automated arthrometer and to evaluate its relationship with patient-reported outcomes (PROMs) and range of motion (ROM) following primary total knee arthroplasty (TKA). Methods This prospective, double-blind cohort study included 80 patients. Either posterior-stabilized (PS) rotating platform (RP) or a fixed bearing cruciate-retaining (CR) design was used. Clinical outcomes were collected preoperatively, at three and 12 months, using the Oxford Knee Score (OKS), Knee injury and Osteoarthritis Outcome Score (KOOS), Patient Knee Implant Performance (PKIP) score, and EQ-5D-5L questionnaire. Sagittal stability was measured using the GNRB/Dyneelax arthrometer. Differences were analyzed using paired t -tests and analysis of variance; correlations and multivariable regression were used to identify predictors of stability. Results All PROMs improved from baseline (p < 0.001). CR knees showed greater early PKIP improvement at three months 12.8 (SD 6.5) vs 8.4 (SD 7.6); p = 0.007). At both three and 12 months, PS knees demonstrated reduced anterior tibial translation across all loads (e.g. 6.2 mm (SD 2.3) vs 4.7 mm (SD 1.6) at 150 N; p = 0.002). Multivariable regression confirmed that implant design (p = 0.016) and sex (p < 0.001) were independent predictors of stability. No correlation was found between sagittal stability and PROMs. Overall, ROM remained unchanged at three months but improved significantly at 12 months. No differences in flexion were noted between the CR and PS groups. Conclusion PS implants demonstrated lower anterior translation under arthrometric testing compared with CR implants. However, this mechanical difference did not translate into superior short-term functional outcomes, and no correlation was found between arthrometric stability and PROMs. ROM improved in both groups without design-related differences. Cite this article: Bone Jt Open 2026;7(11):1429–1438.