Quantification of patella position by ultrasound scanning and its criterion validity.

Altered position of the patella has been associated with patellofemoral joint pain. The main techniques used for assessment of position are either expensive or invasive; there are limited reports of the use of ultrasound (US) scanning to assess patella position. The aim of this study was to establish the validity of a measure of patella position using US scanning compared with those found using magnetic resonance imaging (MRI). MRI and US scans were taken of 20 subjects and analyzed using previously described methods. The correlation between patella position assessed by US scan and lateral patella displacement on MRI showed a good statistically significant correlation (r = 0.64, p = 0.003). The correlation between the patella position assessed by US scan and the equivalent measure on MRI showed an excellent statistically significant correlation (r = 0.78, p = 0.0001). The method described has shown US scanning to be a reliable measure of patella position, with strong criterion validity compared with MRI measures.