Axial knee radiographs: Consistency across clinic sites

Conclusions: Radiographic protocols for knee axial imaging are inconsistent in radiographic positioning and imaging. This variability can lead to disparity in radiographic image results used for clinical decision-making. Standardization of radiographic positioning would yield more consistent imaging of patella position in early flexion, increasing clinical utility and accuracy.

Purpose:

Methods: Radiographic positioning, including beam angle and knee flexion, was measured using a photograph taken of a phantom leg and (human) model set-up. An axial radiograph of a phantom leg was taken at seven different outpatients musculoskeletal clinics to assess patella position (lateral tilt/translation). The phantom leg patella was placed in an abnormal position for the radiographic image across all sites.

Results: Knee flexion <30° was less accurate in obtaining requested knee flexion than higher knee flexion angles (phantom limb error averaged 6°, range 4°–7° human model error averaged 15°, range 11°–25°). Of the five sites utilizing a ‘Merchants’ axial radiographs, the congruence angle varied from +12° to +29°, being normal at one site (+12°) and abnormal (>+16°) at three sites, and negative at one site (−15°).