STUDY DESIGN: Repeated-measures, within-subject design.
OBJECTIVE: To assess the concurrent criterion-related validity and reliability of a clinical device to quantify lateral patellar displacement.
BACKGROUND: Excessive lateral displacement of the patella is an impairment that is widely associated with patellofemoral pain and/or pathology. Currently, no valid or reliable clinical method to assess lateral patellar displacement has been described in the literature.
METHODS AND MEASURES: A total of 26 individuals (14 asymptomatic and 12 symptomatic; mean ± SD age, 27 ± 4 years) participated in the validity portion of this study, while an additional 10 asymptomatic volunteers (mean ± SD age, 28 ± 5 years) participated in the reliability portion. Lateral displacement of the patella was assessed using a custom-designed patellofemoral arthrometer (PFA) and was compared to actual position of the patella as determined by magnetic resonance imaging (MRI). Both PFA and MRI measurements of lateral patellar displacement were made with the knee extended and the quadriceps contracted. The intraclass correlation coefficient (ICC) was used to assess the level of agreement between the PFA and MRI measurements, as well as the intrarater and interrater reliability of the PFA measurements.
RESULTS: The ICC assessing the level of agreement between the MRI and PFA measures of lateral patellar displacement was good (0.86). Excellent intratester (ICC, 0.96 and 0.97) and intertester reliability (ICC, 0.92) were demonstrated.
CONCLUSION: Our results suggest that reasonable estimations of lateral patellar displacement can be obtained using the PFA.

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