Two-dimensional knee valgus displacement as a predictor of patellofemoral pain in adolescent females

Patellofemoral pain (PFP) is a prevalent lower limb musculo-skeletal injury in adolescent females. Female athletes with PFP display increased frontal plane knee joint motion in comparison to control subjects. The current investigation aimed to determine prospectively whether two-dimensional knee valgus displacement during landing could predict the risk of developing PFP. Seventy-six injury-free adolescent female athletes (age = 12.9 ±0.35 years) participated. At baseline participants performed three drop vertical jump trials from a 31-cm box. A standard video camera was used to record frontal plane knee joint kinematics. Over the 24-month follow-up, eight participants developed PFP, as diagnosed by a Chartered Physiotherapist. Knee valgus displacement was significantly increased in those who developed PFP compared to those who did not (mean difference = 7.79°; P = 0.002; partial eta squared = 0.07). Knee valgus displacement ≥10.6° predicted PFP with a sensitivity of 0.75 and specificity of 0.85. The associated positive likelihood ratio was 5. These results have clinical utility suggesting that two-dimensional analysis could be implemented to screen for increased risk of PFP in adolescent female athletes.