Hip AP is a radiography positioning projection of the Pelvis. Supine, affected leg internally rotated 15-20 degrees unless a fracture or dislocation is suspected. SID 40". The centering point is located femoral neck: about 2.5 inches (6 to 7 cm) distal to, and at right angles to, the midpoint of a line between the ASIS and the symphysis pubis. The central ray is perpendicular to the IR, directed to the femoral neck. Image-quality criteria include femoral head, neck, and proximal shaft visible, lesser trochanter not visible, or only minimally, with correct internal rotation. A sample technique is 85 kVp with DR 10 or CR 20 mAs, at an SID of 40 inches (102 cm).
Watch the setup
All steps (4)
- Place the patient supine, arms at the sides or across the upper chest.
- Locate the femoral neck and align it to the CR and the midline of the table.
- Rotate the affected leg internally 15-20 degrees.
- Ensure the pelvis is not rotated: both ASIS the same distance from the table.
3D anatomy: BodyParts3D, © The Database Center for Life Science. Posed, rendered and labelled by RadTechPrepper. These animations are licensed CC BY-SA 4.0. Credits
Anatomy demonstrated
- Femoral head and neck.
- Greater and lesser trochanters.
- Proximal femoral shaft.
- Acetabulum.
- Ischium, pubis, and ilium.
- Hip joint space.
Patient preparation
- WARNING: do not rotate the leg if a fracture or dislocation is suspected. For possible hip or pelvis trauma, complete an AP pelvis including both hips first, without moving the affected leg.
- Verify patient identity using two identifiers.
- Remove all radiopaque objects from the hip region.
- Place the patient supine, arms at the sides or across the upper chest.
- Locate the femoral neck and align it to the CR and the midline of the table.
- Rotate the affected leg internally 15-20 degrees.
- Ensure the pelvis is not rotated: both ASIS the same distance from the table.
Position & centering point
Femoral neck: about 2.5 inches (6 to 7 cm) distal to, and at right angles to, the midpoint of a line between the ASIS and the symphysis pubis.
Central ray
Perpendicular to the IR, directed to the femoral neck.
Exposure / technique
- kVp
- 85
- mAs
- DR 10 / CR 20
- SID
- 40" (102 cm)
- Notes
- Grid required. Sample technique: DR 10 / CR 20 mAs at 85 kVp, 40 in SID, for an 18 cm part (Merrill's sample chart). Adjust for your equipment.
kVp and mAs are sample values. Use caution when applying them in your department.
Image-quality criteria
- Femoral head, neck, and proximal shaft visible.
- Lesser trochanter not visible, or only minimally, with correct internal rotation.
- Margins of the femoral head and acetabulum visualized through the overlying pelvic structures.
- Ischium and pubis visible with minimal distortion.
- No motion blur; bone trabeculae sharp.
- Collimated on four sides to the area of interest, with the entire hip joint and any orthopedic appliance in the field.
Common errors
- 1 Insufficient internal rotation makes the lesser trochanter visible and foreshortens the neck.
- 2 External rotation foreshortens femoral neck and closes acetabulum.
- 3 Pelvic rotation obscures symmetry and distorts anatomy.
- 4 Off-centered CR clips femoral head or excessive pelvis.
- 5 External foot rotation with a visible lesser trochanter typically signals femoral neck fracture: do not correct it.
- 6 Pelvis rotated: check for equal ASIS-to-table distance on both sides.
- 7 Field off-center, so the entire hip joint or orthopedic appliance is not shown.
Clinical indications
- Postoperative or follow-up examination of the acetabulum, femoral head, neck and greater trochanter.
- Possible hip fracture, dislocation or pelvic trauma: complete an AP pelvis first and do not rotate the leg.
- Condition and placement of any existing orthopedic appliance.