118 The Utility of Diagnostic Ultrasound for the Identification of Individuals “At Risk” for the Development of Patellofemoral Joint Osteoarthritis

Abstract

An excessive laterally positioned patella is associated with patellofemoral pain (PFP) and may contribute to patellofemoral joint osteoarthritis (PFJOA). Identifying young adults with PFP is important so that strategies for preventing PFJOA can be started early. Typically, PFP is diagnosed using radiographs, computerized tomography, or magnetic resonance imaging. Diagnostic ultrasound may be a viable alternative since it provides real-time feedback in a cost effective, easily accessible, and safe manner. The purpose of this study was two-fold. The first aim was to establish intra-rater reliability for quantifying patella position using diagnostic ultrasound. The second aim was to determine if individuals with PFP exhibited a more laterally positioned patella than controls when measuring the RAB angle. This was a cross-sectional, observational study. Twenty-three individuals with PFP and 16 controls were included. Patella offset angle (RAB angle) was measured using diagnostic ultrasound. The RAB angle was formed by drawing one line from the femoral trochlea to the center of the infrapatellar fat pad and another from the femoral trochlea to the center of the patella tendon. To establish intra-rater reliability, we assessed the RAB angle for the left and right knee of 4 controls (a total of 8 knees). Although the lead author captured the images and drew the RAB angles, another investigator calculated the values without disclosing them. The procedure was performed twice on each knee. To determine if RAB angles differed between individuals with and without PFP, 2 measures of the most affected knee for subjects with PFP and the right knee for controls were taken. The examiner was blinded to group assignment. The average of the 2 measures was used for data analysis. Intraclass correlation coefficient [ICC3,1] and the standard error of measure (SEM) were used to determine intra-rater reliability; an independent t-test was used to determine between-group differences in RAB angle. The level of significance was established at the 0.05 level. ICC3,1 for the RAB angle measure was 0.94 with a SEM of 3.9°. Subjects with PFP had a greater RAB angle than controls (13.9° versus 5.8°; t=2.4; P=0.02), suggestive of a more laterally positioned patella. Results from this investigation showed that measuring the RAB angle with diagnostic ultrasound provided a reliable measure. More importantly, these results showed that individuals with PFP exhibited a more laterally positioned patella than controls. These findings are clinically relevant, given that PFP can progress to PFJOA. Conservative treatment (eg, physical therapy) has been the recommended treatment for PFP. Early identification and referral to rehabilitation for this cohort may prevent or delay the onset of PFJOA. However, future investigations are needed to make this determination.