Radiography of the knee joint : a comparative study of the standing partial flexion PA projection and the standing fully extended AP projection using visual grading characteristics (VGC)

Abstract

Objectives: To compare the diagnostic information in detection and assessment of knee pathology from knee radiographs using either the PA standing with partial flexion projection or AP fully extended standing projection.

Method: A set of 32 knee radiographs was retrospectively compiled from 16 adult patients imaged using both projections over a 2-year period (PA: n ¼ 16 and AP: n ¼ 16). Repeat radiographs (n ¼ 6) were added to the image set facilitating inter and intra observer reliability. Image evaluation was performed by 5 orthopaedic surgeons performing Absolute Visual Grading Analysis assessing image quality based on 6 anatomical image quality criteria specifically developed to evaluate and compare the two projections. The resulting image quality scores were analysed using Visual Grading Characteristics.

Results: Image quality scores were higher for the PA projection but variation between the two projections was not significant (p > 0.05). The PA projection was significantly (p < 0.05) better in the visualization of 2 anatomical image quality criteria involving the joint space width and tibial spines.

Conclusion: Both projections can be used for general evaluation of the knee joint, however the PA partial flexion projection is preferred for the investigation of specific knee pathology. Recommendations for minimizing variations in radiographic positioning technique are also highlighted.