Ultrasound measurements for patellofemoral pain syndrome: An inter-operator reliability study

Abstract Background Radiological and ultrasound measurements are commonly used in the diagnosis of patellofemoral pain syndrome (PFPS), as no clinical tests have yet demonstrated good reliability or validity. We studied the degree of agreement between two examiners for the qualitative and quantitative criteria used for the diagnosis of PFPS. Methodology Forty-one adults with chronic anterior knee pain for over 2 months were selected consecutively in a hospital's orthopaedic department. They were referred to one junior and to one senior radiologist, who evaluated the positive or negative nature of three ultrasound criteria: the presence of a dysplasia, the distance between patellar tip and trochlear groove (PTTG) during maximal quadriceps contraction, and the cartilaginous trochlear groove (CTG) angle. Each sonographic examination was performed with the radiologist blinded to the clinical details and to the other radiologist's findings. Results The Cohen's Kappa and prevalence and bias adjusted Kappa (PABAK) values were poor for the ultrasound CTG angle criterion (PABAK = 0.55; kappa = 0.52) and moderate for the ultrasound PTTG distance criterion (PABAK = 0.35; kappa = 0.36). It was not possible to calculate Kappa or PABAK values for the dysplasia criterion because of very low prevalence. Conclusion Quantitative ultrasound criteria for PFPS can be reliable if performed in a standardized manner and by trained practitioners. Only the PTTG distance criterion showed a clinically acceptable inter-operator reliability level.