RadSetu

X-ray Positioning

AP knee

Radiographic projections, patient positioning and X-ray references.

Method & scope

Patient position

  • Supine, leg fully extended, pelvis not rotated.
  • Leg internally rotated 3–5° so the epicondyles are parallel to the IR.
  • Measure ASIS to tabletop to choose the CR angle.

Centering

1.25 cm (½″) distal to the apex of the patella.

Central ray

Parallel to the tibial plateau: 0° for 19–24 cm ASIS–tabletop; 3–5° cephalic if > 24 cm; 3–5° caudal if < 19 cm.

Source-to-image distance

100 cm (40″).

Image evaluation

  • Open femorotibial joint space, equal medial and lateral
  • Femoral and tibial condyles symmetric
  • Tibia overlaps about half of the fibular head