Limb support in response to balance provocations in women with patellofemoral pain

Abstract

Chronic pain may modulate motor strategies not only in the presence of pain but also in pain-free periods. Patellofemoral pain (PFP) is characterized by intermittent periods with knee pain. The aim of this study was to examine whether long-term pain would affect lower limb support and trunk movement in unpredictable external and predictable internal balance perturbations in women with PFP with no acute pain, compared with healthy controls. We hypothesized that long-term pain would induce compensatory strategies to minimize joint loading in the affected knee and that healthy control subjects without any knee problems would rely equally on both limbs. We also hypothesized that handed- and footedness would influence trunk rotation and movement of the body's centre of mass in predictable perturbations and would be influenced by unloading of the affected limb in PFP. The results showed that controls relied more on the preferred leg and that PFP subjects avoided loading on the affected limb, even when it was preferred, except during unpredictable perturbations where a symmetrical postural response appeared to override limb protection or the habitual unloading. Thus, compensatory strategies in PFP subjects become well established in the motor behaviour and can thus be identified even in pain-free periods.