People With Patellofemoral Pain Have Bilateral Deficits in Physical Performance Regardless of Pain Laterality

Abstract

Context: People with patellofemoral pain (PFP) may have lower performance during the forward step-down and single-leg hop with their painful (unilateral complaints) or most painful (bilateral complaints) limb when compared with pain-free controls. However, no authors have investigated the appropriateness of using the pain-free or less painful limb as a reference standard in clinical practice or whether deficits might be present depending on the laterality of pain.

Objective: To compare performance scores and proportion of side-to-side limb symmetry during the forward step-down and single-leg hop tests among people with unilateral and bilateral PFP and pain-free controls.

Design: Cross-sectional study.

Setting: Laboratory.

Patients or other participants: Fifty-two young adults (18-35 years old) with unilateral PFP, 72 with bilateral PFP, and 76 controls.

Main outcome measure(s): Group × limb interactions on performance during the step-down (repetitions) and single-leg hop (distance [cm] normalized by the limb length) tests were investigated using a repeated-measures analysis of covariance controlling for sex. Pairwise comparisons were interpreted using effect sizes. A χ2 test was used to compare the proportion of symmetry/asymmetry (cutoff point of ≥90% for symmetry indices) across groups and tests.

Results: Main effects for groups (small to medium effects) but not limbs indicated lower performance of both limbs of individuals with unilateral and bilateral PFP than controls during forward step-down and single-leg hop tests. No significant differences for the proportion of symmetry/asymmetry were identified across groups (P ≥.05), which further suggests an impaired physical performance of the contralateral limb.

Conclusions: Our results indicate bilateral deficits in the physical performance of people with unilateral and bilateral PFP when compared with pain-free controls during the forward step-down and single-leg hop tests. Limb symmetry indices greater than 90% should be interpreted with caution, as they may overstate physical performance by not assuming bilateral deficits.

Keywords: anterior knee pain; assessment; clinical tests; functional capacity; objective function.