AP femur X-ray positioning
One of the routine femur views. The patient lies on their back, the beam passes front to back (AP), straight on to the receptor, and the centring point is the mid-shaft.
By the ScanFlo Editorial Team · Updated
In this section · X-ray positioning
- X-ray positioning guides
- Skull positioning
- Face & sinuses positioning
- Soft tissue neck positioning
- C-spine positioning
- Chest positioning
- Shoulder positioning
- Humerus positioning
- Elbow positioning
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- Wrist positioning
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- Abdomen positioning
- L-spine positioning
- Sacrum & SI joints positioning
- Pelvis positioning
- Hip positioning
- Femur positioning
- Knee positioning
- Tibia & fibula positioning
- Ankle positioning
- Foot positioning
Still being checked: a radiographer is reviewing this guide. If your department does it differently, follow your department.
Patient position
Supine. Supine; if not injured turn the foot in. If injured, do not move the foot and include the joint nearest the injury.
Centring & collimation
Central ray
APCentre: the mid-shaft.
Beam: AP, perpendicular to the receptor.
Collimate: the joint nearest the injury and the whole shaft
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 18 × 43 cm | portrait |
| Placement | Table bucky | Grid in |
| Angulation | None | Perpendicular to the receptor |
Marker & breathing
- Marker: R or L marker on the side nearest the detector
- Breathing: Suspend respiration.
Exposure by patient size
Treat these as a starting point. Your detector, your generator and the patient in front of you will all move the numbers.
| Patient size | kV | mAs (chart) | mAs (DR default) |
|---|---|---|---|
| XS | 70 | 6.3 | 4 |
| S | 70 | 10 | 6.3 |
| M | 70 | 12.5 | 8 |
| L | 70 | 20 | 12.5 |
| Child | 53 | 2 | 1.25 |
These start from a classic film-screen chart (70 kV, 25 mAs at 140 cm) and are adjusted for a digital detector at 100 cm. The DR column is what ScanFlo's console suggests; each step up or down changes the mAs by about a quarter.
Image quality checklist
- The image includes the joint closest to the injured site, at minimum.
- No rotation.
- The anatomical side marker is visible, correct and clear of the anatomy.
- Collimation borders are visible on all sides, no wider than the area requested.
Faults & how to fix them
| Fault | Cause | Fix |
|---|---|---|
| Joint missed | Field too short | Take a second film for the other end. |
Common questions
- Where do you centre for a femur AP X-ray?
- The centring point is the mid-shaft.
- What distance and beam angle does a femur AP need?
- 100 cm from the tube to the receptor. The beam passes front to back (AP), straight on to the receptor.
- What size receptor, and do you need a grid?
- Use an 18 × 43 cm receptor, portrait, in the table bucky. A grid is needed.
- What should the patient do with their breathing?
- Ask them to stop breathing for the moment of the exposure.
- What goes wrong most often on a femur AP?
- Joint missed. Usual cause: field too short. The fix: take a second film for the other end.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a femur ap in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.