The effects of three quarter and full length foot orthoses on knee mechanics in healthy subjects and patellofemoral pain patients when walking and descending stairs

•Important differences in knee mechanics exist between the PFP and healthy group.•Foot orthoses normalise the coronal plane knee moment in PFP patients.•Changes in foot orthotic prescription impact on foot and knee mechanics. An increased load of the patellofemoral joint is often attributed to foot function in patients with patellofemoral pain. Foot orthoses are commonly prescribed for this condition; however the mechanisms by which they work are poorly understood. The aim of this study was to investigate the kinematics and kinetics of the knee between patellofemoral pain patients and a group of healthy subjects when using a standardised foot orthosis prescription during walking and step descent. Fifteen healthy subjects and fifteen patients diagnosed with PFP with a foot posture index greater than 6, had foot orthoses moulded to their feet. They were asked to walk at a self-selected pace and complete a 20 cm step descent using customised orthoses with ¾ and full length wedges. Kinematic and Kinetic data were collected and modelled using Calibrated Anatomical System Technique. Significant differences were seen in both the kinematics and kinetics between the healthy group and the PFP patients at the knee. A significant reduction in the knee coronal plane moment was found during the forward continuum phase of step descent when wearing the foot orthoses; this was attributed to a change in the ground reaction force as there were no changes reported in the kinematics of the knee with the orthoses. This study identified potentially clinically important differences in the knee mechanics between the PFP patients and the healthy group during walking and step descent. The foot orthoses reduced the coronal plane knee moment in the PFP patients to a value similar to that of the healthy subjects with no intervention.