Neuromuscular activity and knee kinematics in adolescents with patellofemoral pain.

PURPOSE: This study aimed to investigate the neuromuscular control of the knee during stair descent among female adolescents with patellofemoral pain (PFP) and to report its association with self-reported clinical status assessed by the Knee Injury and Osteoarthritis Outcome Score (KOOS).
METHODS: Fifty-seven previously untreated female adolescents diagnosed with PFP ages 15-19 yr were recruited from schools. The control group consisted of 29 age-matched healthy female adolescents. Bipolar surface electrodes were placed on vastus medialis and vastus lateralis, and an electronic knee goniometer was placed at the knee to collect knee flexion/extension kinematics. The participants walked down a stairway consisting of 24 steps at their normal pace. Sample entropy was used to quantify the complexity of the time series from surface electromyography and kinematics during the stance phase. Self-reported clinical status was assessed by the KOOS and the maximal quadriceps torque measured using strap-mounted handheld dynamometry.
RESULTS: Female adolescents with PFP were characterized by altered neuromuscular knee control during stair descent, lower maximal quadriceps torque, and poorer KOOS scores across all five domains. Furthermore, a positive association was found between the complexity of surface electromyography from vastus lateralis and self-reported pain determined by KOOSpain, indicating larger impairments in neuromuscular knee control among those with the highest pain levels.
CONCLUSIONS: The current findings show that female adolescents with PFP are characterized by altered neuromuscular control of the knee during stair descent and lower maximal quadriceps torque. These results suggest that rehabilitation is needed and should focus on restoring neuromuscular control and muscle strength.