The analysis of the plain radiography of the knee is complex because of an overlap of several anatomical components. On postero-anterior and lateral radiographs it is possible to describe both medial and lateral femoral and tibial surfaces, patellar tilt, femoral trochlear dysplasia and abraded subchondral bone. Often, a false joint spaces is described because of non weight-bearing views. The sky-line or axial view has long been known to provide useful information about morphology and anatomy of the patellofemoral joint. The aim of the study was...

Twenty volunteers (10 females and 10 men, mean age 50, range 35- 65) underwent two consecutive X-rays of both patella using the "sky-line view". In the same session the internal tibio-femoral joint of all volunteers were imaged by two consecutive postero-anterior views taken with the patient bearing weight in full extension (Fig.1, Fig.2). Two indipendent radiologists manually measured the internal tibio-femoral space and femoro- patellar space (FPS). The interobsever and intraobserver agreement was evaluated. Twenty consecutive patients underwent a knee CTA. Before performing CTA, each...

There was a strong interobserver and intraobserver agreement (k=0.85) for the measurements of the FPS under charge using a standardized "sky-line" view, with good reproducibility of the measurement (mean error 6% of measurement between two consecutive acquisitions in the same position, comparable to that found in tibio-femoral joint). A very good correlation was found between the measurements of external patello-femoral at X-rays and measurement at CTA especially for the sample located at or below the equator of the patella.

It can be difficult to obtain images of the patellofemoral joint in a consistent manner without a trained technician. "Sky-line" X-rays of the femoro-patellar joint under charge performed with a standardized technique allows an effective measurement of the FPS. The measurements are strongly correlated to the cartilage thickness of the patella as measured at CTA.

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