Knee - AP |

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Radiographic Positioning


Adult
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Name of projection Knee - AP
Area Covered Distal femur, proximal tibia & fibula, patella, and knee joint.
Pathology shown Any fractures, lesions, or bony changes secondary to degenerative joint disease.
Radiographic Anatomy Knee Radiographic Anatomy
IR Size & Orientation 18 x 24cm
Portrait
Film / Screen Combination Detail
(CR and DR as recommended by manufacturer)
Bucky / Grid No
Filter No
Exposure 60 kVp
8 mAs
FFD100 cm
Central Ray Directed parallel to the tibial plateau, approximately 1.5cm distal to apex of the patella
Central ray angle
  • 5° caudad for thinner leg
  • 0° for normal leg
  • 5° cephalad for thicker leg
Collimation Centre:
Shutter A: Open to film size superiorly and inferiorly
Shutter B: Open to include lateral skin margins
Markers Distal and Lateral
Marker orientation AP
Shielding Gonadal (check your department's policy guidelines)
Respiration Not applicable
Positioning
                • Patient supine on the X-ray table
                • Cushion for head
                • Align and center leg and knee to CR and to midline of IR.
                • Rotate leg internally 3° to 5° for true AP (or until interepicondylar line is parallel to plane of IR.)
                • Place sandbags by foot and ankle to stabilise if needed.
                Critique

                		 Positioning
                • No rotation will be evident by the symmetric appearance of the femoral and tibial condyles and the joint should be superimposed by the tibia.
                • The intercondylar eminence will be seen in the center of the intercondylar fossa.
                Area Covered
                • The distal femur and proximal tibia and fibula are shown.
                • The femorotibial joint space should be open, with the articular facets of the tibia seen on end with only minimal surface area visualized.
                Collimation
                • The collimation field should align with the long axis of the IR.
                • The center of the collimation field should be to the midknee joint space.
                Exposure
                • Optimal exposure will visualise the outline of the patella through the distal femur, and the fibular head and neck will not appear overexposed.
                • No motion should exist; trabecular markings of all bones should be visible and appear sharp. Soft-tissue detail should be visible.
                Special Notes