Skyline (sunrise) patella X-ray positioning (axial)
An extra knee view, used when a routine one is not enough. The patient stands, the beam runs along the length of the part (axial), straight on to the receptor, and the centring point is the patella.
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
- Forearm positioning
- Wrist positioning
- Hand positioning
- T-spine positioning
- 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
Erect. The patient stands with the foot on a 25 cm support, knee flexed over the detector placed on the support.
Centring & collimation
Central ray
axialCentre: the patella.
Beam: axial, perpendicular to the receptor.
Collimate: the patellofemoral joint
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 18 × 24 cm | landscape |
| Placement | On a raised support | 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 | 1 | 0.5 |
| S | 53 | 1.6 | 0.63 |
| M | 53 | 2 | 0.8 |
| L | 53 | 3.2 | 1.25 |
These start from a classic film-screen chart (53 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 patellofemoral joint space is shown.
- 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 not open | Flexion wrong | Adjust flexion. |
Common questions
- Where do you centre for a patella axial (skyline) X-ray?
- The centring point is the patella.
- What distance and beam angle does a patella axial (skyline) need?
- 100 cm from the tube to the receptor. The beam runs along the length of the part (axial), straight on to the receptor.
- What size receptor, and do you need a grid?
- Use an 18 × 24 cm receptor, landscape, on a raised support. 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 a patella axial (skyline)?
- Joint not open. Usual cause: flexion wrong. The fix: adjust flexion.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a patella axial (skyline) in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.