Knee internal contact force in a varus malaligned phenotype in knee osteoarthritis (KOA)

Purpose :Multiple phenotypes characterized by different disease mechanisms have been hypothesized to explain the large variability in the knee osteoarthritis (KOA) population. The purpose of this study was: to estimate and compare the medial and lateral knee compression forces (CF) during gait of three subgroups of KOA subjects characterized by different alignment and cartilage disruption patterns. 
Methods:A secondary data analysis was conducted on a sample of 39 KOA subjects and 18 controls (C). The patients were classified in the different groups according to the following criteria: Varus medial disease (VMD) (12): varus alignment and predominant medial cartilage degeneration Varus generalized disease (VGD) (17): varus alignment and cartilage degeneration that extends to the lateral compartment. Neutral alignment (NA) (10): neutral alignment. The total, medial and lateral CF corrected for body weight were estimated using an inverse dynamics model (AnyBody Modeling System, AnyBody Technology) during stance. 
Results:The impulse of the medial compressive force (MCF) (overall effect of the CF over the stance) was significantly higher (P <0.01) in the VMD compared to all the other groups. Peak MCF was higher in the VMD compared to all the other groups, but the difference reached significance only when compared to the VGD group (P <0.05). The results of the regression analysis showed a significant relationship in the VMD group between alignment and impulse of the MCF (R2 = 0.62; P <0.01). This relationship disappears in the other groups. Conclusions These findings suggest the existence of a phenotype characterized by increased MCF.