Effect Of Strike Pattern And Step Cadence On Patellofemoral Joint Stress In Runners With Patellofemoral Pain

Objective:Patellofemoral pain syndrome is a common sports injury of knee joint,which occurs more frequently in runners.The main manifestation is the pain around patella while walking,running or squatting.If there is no timely intervention and treatment,it will eventually develop into irreversible patellofemoral arthritis.More and more researchers have paid attention to the prevention of sports injury by adjusting the biomechanics of lower extremity by changing runners’ strike pattern and step cadence.The purpose of this study was to determine the effect of strike pattern and step cadence on patellofemoral joint stress and three-dimensional(3D)kinematic and kinetic variables of lower extremity while running in runners with patellofemoral pain,so as to provide valuable guidance for runners with patellofemoral pain.Methods: A total of 20 male runners with patellofemoral pain who met the inclusion criteria were recruited.Each subject randomly completed running tests of three different step cadence conditions(10% decreased,preferred and 10% increased)in different strike patterns(rearfoot and forefoot)at their self-selected running speed.Three dimensional kinematics and three dimensional ground reaction force data of lower extremity during running were collected using a Vicon 3D motion capture system and a Bertec instrumented treadmill.Visual 3D software was used to process the data,and the data was expressed in the form of mean ± standard deviation.Two-factor repeated measurement ANOVA was used to compare the effects of strike pattern and step cadence on patellofemoral joint contact force(PFCF),patellofemoral joint stress(PFJS),the three-dimensional joint range of motion,peak angle,peak moment and ground reaction force of lower extremity joints.The significance level was set as P < 0.05.Results:1.Patellofemoral joint stress: Compared with rearfoot strike pattern(RFS),patellofemoral joint contact force(P<0.001)and patellofemoral joint stress(P<0.001)were significantly lower in the forefoot strike(FFS)across all step rate conditions.In both strike patterns,a 10% decrease in step cadence resulted in greater patellofemoral contact force(P=0.03)and patellofemoral stress(P=0.001),and a10% increase in step cadence resulted in lower patellofemoral contact force(P=0.011)and patellofemoral stress(P=0.029),compared with the preferred step cadence.There was no significant interaction between strike pattern and step cadence on patellofemoral joint contact force and patellofemoral joint stress.2.Range of motion: Across all step cadence conditions,hip sagittal plane ROM(P<0.001),hip coronal plane ROM(P<0.001),hip horizontal plane ROM(P<0.001),knee sagittal plane ROM(P=0.001)and knee coronal plane ROM(P=0.001)were lower while running with a FFS pattern than when use a RFS pattern.Ankle sagittal plane ROM(P<0.001)was higher while running with a FFS pattern than when use a RFS pattern.In both strike patterns,a 10% decrease in step cadence resulted in greater hip sagittal plane ROM(P=0.001),greater hip coronal plane ROM(P<0.001),greater knee sagittal plane ROM(P<0.001),greater ankle sagittal plane ROM(P<0.001)and greater ankle horizontal plan ROM(P=0.014)compared with the preferred step cadence.A 10% increase in step cadence resulted in smaller knee sagittal plane ROM(P<0.001),smaller ankle sagittal plane ROM(P=0.005)and smaller ankle horizontal plan ROM(P=0.008)compared with the preferred step cadence.There was no significant interaction between strike pattern and step cadence on ROM of hip,knee and ankle joint.3.Peak joint Angle: Across all step cadence conditions,participants experienced a smaller peak hip flexion Angle(P<0.001),peak hip adduction peak Angle(P<0.001),peak knee peak flexion Angle(P=0.003),peak knee eversion Angle(P=0.006),peak ankle dorsiflexion Angle(P<0.001),peak ankle eversion Angle(P<0.001)and peak ankle external rotation Angle(P<0.001)while running with a FFS pattern than when use a RFS pattern.In two strike pattern conditions,the peak Angle of hip flexion(P=0.033),peak Angle of knee flexion(P=0.012),and peak Angle of knee internal rotation(P=0.029)were grater when the step cadence decreased by10% compared with the preferred step cadence.What’s more,a 10% increase in step cadence resulted in a smaller peak Angle of knee flexion(P=0.036)and peak Angle of ankle plantar flexion(P=0.023)compared with the preferred step cadence.Different strike pattern and step cadence had significant interaction on the peak Angle of hip extension and ankle internal rotation,but had no statistical difference on the interaction of other peak Angle indexes.Further analysis showed that the strike pattern had no significant influence on peak Angle of hip extension at preferred step cadence.With a 10% reduction in step cadence,the FFS pattern had a smaller peak Angle of hip extension compared with RFS pattern.With a 10%increase in step cadence,the FFS pattern had a greater peak Angle of hip extension compared with RFS pattern.What’s more,during the FFS pattern,there was no significant difference on the peak Angle of hip extension across different step cadence conditions.During the RFS pattern,a 10% increase in step cadence resulted in a larger peak extension Angle(P=0.023)than a 10% decrease in step cadence(P=0.023).As for the peak Angle of ankle internal rotation,the results showed that there was no significant difference between strike pattern while in preferred step cadence and 10% decrease step cadence.With a 10% increase in step cadence,there was a greater peak Angle of ankle internal rotation in the FFS pattern than in the RFS pattern(P=0.004).In addition,during the FFS pattern,there was no significant difference in the peak Angle of ankle internal rotation across three step cadence conditions.In the RFS pattern,the peak Angle of ankle internal rotation was larger at the preferred step cadence(P=0.049)and the 10% decreased step cadence(P=0.002)than a 10% increased step cadence(P=0.002).4.Peak joint Moment: Across all step cadence conditions,compared with RFS pattern,hip extension peak moment(P<0.001),hip adduction peak moment(P=0.005),knee extension peak moment(P<0.001),knee eversion peak moment(P=0.02)and ankle dorsiflexion peak moment(P<0.001)were lower in the FFS pattern;knee flexion peak moment(P=0.007),ankle plantar flexion peak moment(P<0.001)and ankle external rotation peak moment(P=0.026)were greater in FFS pattern.In two strike pattern conditions,compared with the preferred step cadence,hip extension peak moment(P=0.002),hip external rotation peak moment(P=0.022)were greater when the step cadence decreased by 10%.Strike pattern and step cadence had significant interaction on the peak moment of ankle external rotation,but had no statistical difference on the interaction of other peak moment indexes.5.Ground reaction force: Across all step cadence conditions,and compared with RFS pattern,anterior peak ground reaction force(P<0.001)and vertical peak ground reaction force(P<0.001)were greater in FFS pattern,lateral peak ground reaction force(P<0.001)and medial peak ground reaction force(P=0.003)were smaller in FFS pattern.In two strike pattern conditions,compared with preferred step cadence,lateral peak ground reaction force(P=0.045)was greater when the step cadence decreased by 10%.There was no significant interaction between strike pattern and step cadence on ground reaction force.Conclusion: For runners with PFPS,immediately changing the strike pattern from RFS to FFS can reduce patellofemoral joint stress,reduce the range of motion of hip and knee joint,and increase the range of motion of ankle joint.Immediately increasing the step cadence can reduce the patellofemoral joint stress and reduce the knee flexion Angle during stance.This study confirmed that the combination of FFS pattern and increased step cadence can maximize the reduction of patellofemoral joint stress,thereby reducing the patellofemoral joint load.However,it should be noted that changing to a FFS pattern and increasing step cadence will increase the ankle plantarflexion moment and may increase the risk of ankle injury.Therefore,it should be used with caution in PFPS runners who also have ankle injuries.