The Patellostabilometer: A New Device for Quantification of Mediolateral Patella Displacement

(1) Background: The mediolateral patella displacement is of interest for diagnostics and clinically relevant research questions. Apart from manual testing, no standardized method is currently available. Proper quantification of patella mobility is necessary to understand pathologies at the patellofemoral joint better; (2) Methods: Patella mobility was assessed in 25 healthy individuals using a Patellostabilometer, a new prototype instrument for quantification of the mediolateral patella displacement. The participants underwent measurements of the mediolateral displacement three times using the Patellostabilometer. A maximal force of 10N was applied for patella movement. Additionally, leg length, circumference of the knee, upper- and lower leg was measured. (3) Results: Lateral patella displacement of 18.27±3.76 mm (range 15.85-20.64mm, interquartile range (IQR) of 4.79) was measured. The medial patella displacement showed 24.47±6.59mm (range 19.29-29.76mm, IQR of 10.47). The test-retest measurement error was 2.32±1.76mm (IQR of 2.38mm), with five outliers. There was greater test-retest variability between the measurements of the medial displacement comparing to the lateral one (4) Conclusions: The test-retest variability reached 7% of the patella displacement. Other parameters provided no significant correlations. Based on the natural patellofemoral mobility a precise and clinically relevant quantification of patella mobility is allowed.