A Vasti Medialis Nerve Block Alters in Vivo Knee Joint Kinematics: Implications for Patellofemoral Pain Syndrome

INTRODUCTION: Patellofemoral (PF) pain syndrome (PFPS) is one of the most common problems of the knee. A potential source of this pain is a force imbalance around the knee leading pathological PF kinematic (maltracking). In turn, this causes elevated joint contact stresses, which ultimately results in PF pain. The source of this force imbalance is still open to debate with some postulating the cause to be delayed timing or loss of strength in the vasti medialis (VM) [1]. Yet, numerous studies refute these claims as well [2]. Since muscle force cannot be measured directly, without highly invasive techniques, previous studies have relied on electromyography (EMG). Yet in patients with PFPS the assumptions required to estimate muscle force from EMG may not be valid [3]. Thus, the purpose of this study was to determine how a loss of VM force alters 3D in vivo PF and tibiofemoral (TF) kinematics during a volitional extension task.