Ultrasound Measurement of Lateral Patellar Displacement: A Cadaveric Validation Study.

Background: Patellofemoral pain syndrome (PFPS) is one of the most common musculoskeletal complaints seen in outpatient settings. It has been suggested that hip adduction creates loads on the iliotibial band and causes lateral displacement of the patella (patellar tilt), which can lead to uneven patellofemoral joint loading, and hence, cause patellofemoral pain. In previous studies in the literature, ultrasound has been used to measure lateral patellar displacement. However, the method lacks validity data. Purpose/Hypothesis: The aim of this study was to validate the use of ultrasound to measure lateral displacement of the patella, by comparing the position of the patella as measured first by ultrasound, and then by direct measurement. Study Design: Descriptive Laboratory Study. Methods: Nine soft-fixed cadavers were used in this study. The cadavers had been donated for anatomical examination and research under the Human Tissue Act (2004). The distance between the lateral femoral condyle and the lateral edge of the patella were measured by B-mode real-time ultrasound, and then by direct measurement, in two positions, neutral and at 20° hip adduction. Results: The mean difference in the patella-to-lateral femoral condyle distance in the neutral position and at 20° adduction was 0.27 cm (ultrasound), and 0.34 cm (direct measurement), respectively. There were no significant differences between the measurements obtained by US and by direct measurement (Pearson correlation= 0.97, p=0.83). Conclusion: Ultrasound is a valid and reliable method for measuring patellar position relative to the femoral condyle, and the validity data reported here suggest that it can be used with confidence in clinic to assess lateral patellar displacement. Level of Evidence: 3.