External oblique ankle X-ray positioning
An extra ankle view, used when a routine one is not enough. The patient lies on their back, the beam passes front to back (AP), straight on to the receptor, and the centring point is midway between the malleoli.
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. On request: heel on the detector, foot rotated out to 30°.
Centring & collimation
Central ray
APCentre: midway between the malleoli.
Beam: AP, perpendicular to the receptor.
Collimate: the ankle
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 18 × 24 cm | portrait |
| Placement | Tabletop | No grid |
| Angulation | None | Perpendicular to the receptor |
Marker & breathing
- Marker: R or L marker on the side nearest the detector
- Breathing: No breathing instruction needed.
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 | 53 | 0.8 | 0.5 |
| S | 53 | 1.25 | 0.5 |
| M | 53 | 1.6 | 0.63 |
| L | 53 | 2.5 | 1 |
These start from a classic film-screen chart (53 kV, 20 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 medial malleolus is shown in profile.
- 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 |
|---|---|---|
| Too little rotation | No angle guide | Use a 30° pad. |
Common questions
- Where do you centre for an ankle external oblique X-ray?
- The centring point is midway between the malleoli.
- What distance and beam angle does an ankle external oblique 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 × 24 cm receptor, portrait, on the tabletop. No grid is needed.
- Where does the lead marker go?
- R or L marker on the side nearest the detector.
- What goes wrong most often on an ankle external oblique?
- Too little rotation. Usual cause: no angle guide. The fix: use a 30° pad.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a ankle external oblique in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.