Kinematical patterns through Dynamic RSA reflected clinical outcomes improvement during at two years follow-up

Introduction: A new concept of total knee arthroplasty (TKA), the medial-stabilized (MS) knee prosthesis, has been developed trying to mimic distal femur and tibial plateau geometry, thus reproducing the natural knee motion. However, the relationship between knee motion and patients’ satisfaction is still unclear. The use dynamic radiostereometric analysis (RSA) could be useful in predicting the clinical outcomes through kinematical patterns. The aim of the study was to evaluate the clinical outcomes and the kinematical pattern of the MS TKA during a two-follow-up period. We hypothesized that (1) an improvement in clinical outcomes and (2) coherent changes in kinematical patterns. Material and methods: 10 patients were evaluated through clinical and functional scores evaluation (Knee Society Score -KSS, Womac, Oxford), and kinematically through dynamic RSA at minimum 9 months (FU1) and at 2 years (FU2) after MS-TKA, during the execution of a sit-to-stand. The clinical and kinematical differences were evaluated through Student’s t test (p < 0.05) and a correlation analysis between score improvement and kinematics was performed through the Pearson’s correlation coefficient r. Results: A significantly greater (p < 0.001) anterior translation of the lateral compartment with respect to the medial one was found in both FU1 (medial 2.6 mm ± 0.8 mm, lateral 8.3 mm ± 2.8 mm) and FU2 (medial 1.4 mm ± 0.5 mm, lateral 7.3 mm ± 3.0 mm), thus resulting in a medial pivot pattern. Significant improvement of KSS clinical was found (delta 20.3, p=0.018), while the other scores remained stable. Significant correlations were found between KSS clinical improvement and laxity reduction, particularly with peak external rotation (r=0.47), peak anterior translation (r=0.62), varus-valgus rotation (r=0.75). Interpretation and Conclusions: Clinical outcomes either improved or remained stable between FU1 and FU2 and a medial pivot pattern was confirmed. Laxity reduction evaluated through Dynamic RSA concretely reflected the patients’ clinical improvement.