An instruction as a modifier of dynamic knee valgus in adolescents with patellofemoral pain

Patellofemoral pain (PFP) is a prevalent condition among adolescents. An altered neuromuscular control, particularly poor control of dynamic knee valgus (DKV), can potentially exacerbate or trigger PFP. The present study aimed to analyze the effects of instruction in a functional test on DKV control, gluteus medius (Gmed) muscle activity, and pain in adolescents with PFP.

Quasi-experimental design. Fourteen lower limbs with PFP (PFPG) and 12 lower limbs in the control group (CG) were evaluated. The Frontal Plane Projection Angle (FPPA) and Gmed activation were evaluated during the Lateral Step Down test through a motion analysis system and surface electromyography, respectively, before and after the DKV instruction. Pain was assessed using the Numeric Pain Rating Scale. The CG was assessed only in the pre-test condition.

The instruction decreased (-72 %) the FPPA value (p < 0.001, effect size = 1.8, power = 0.99). Responsiveness was noted in 92.9 % of the lower limbs. Post-test, the PFPG demonstrated a similar pattern to the CG regarding DKV (p = 0.388). Activation of Gmed was higher in the PFPG compared to the CG in the pre-instruction (p = 0.03) but did not change post-instruction (p = 0.08, effect size = 0.44, power = 0.20). The responsiveness for Gmed activation was 71.4 %. Reported pain did not changed (p = 0.172, effect size = 0.46, power = 0.22).

An instruction promotes better control of DKV movements. However, the instruction did not alter Gmed muscle activity or reported pain.