Radiological measurements in patellofemoral disorders. A review

This paper analyzes some of the radiologic measurements used in the diagnosis and management of patellofemoral disorders. Measurements such as condylar width and height and patellar height from the true lateral view are helpful to determine the type and severity of intercondylar dysplasia. Skyline views provide information on the type and degree of patellar subluxation and dysplasia, especially of the medial aspect of the trochlear groove. In asymptomatic subjects, the trochlear angle does not exceed 140 degrees, and the lateral medial intercondylar ratio in dysplasia is > 1.7. Scanograms specifically assess the longitudinal axis of the lower limb. Computed tomography (CT) measurements for patellar subluxation do not provide significant additional information over that provided by skyline views. The average distance between the anterior tibial tuberosity and the trochlear groove is normally 13 mm, and a distance > 20 mm associated with knee pain should probably warrant surgery. Because of multiplanar facilities and exposure to nonionizing radiations, magnetic resonance imaging is progressively replacing CT scanning for quantitative and qualitative measurements, at least in a research environment. Its use in routine clinical practice is not yet warranted, given its high costs.