Lateral sacrum and coccyx X-ray positioning
An extra sacrum & SI joints view, used when a routine one is not enough. The patient lies on their side, the beam passes from side to side, straight on to the receptor, and the centring point is the sacrum, 10 cm posterior to the anterior superior iliac spine.
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
X-ray positioning/Sacrum & SI joints
Still being checked: a radiographer is reviewing this guide. If your department does it differently, follow your department.
Patient position
Lateral recumbent. Lateral with knees bent and the spine horizontal.
Centring & collimation
Central ray
lateralCentre: the sacrum, 10 cm posterior to the anterior superior iliac spine.
Beam: lateral, perpendicular to the receptor.
Collimate: sacrum and coccyx
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 24 × 30 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 | 90 | 32 | 12.5 |
| S | 90 | 50 | 20 |
| M | 90 | 63 | 25 |
| L | 90 | 100 | 40 |
These start from a classic film-screen chart (90 kV, 100 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
- Sacrum and coccyx 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 |
|---|---|---|
| Coccyx burnt out | Sacral exposure | Collimate and reduce mAs for the coccyx. |
Common questions
- Where do you centre for a sacrum and coccyx lateral X-ray?
- The centring point is the sacrum, 10 cm posterior to the anterior superior iliac spine.
- What distance and beam angle does a sacrum and coccyx lateral need?
- 100 cm from the tube to the receptor. The beam passes from side to side, straight on to the receptor.
- What size receptor, and do you need a grid?
- Use a 24 × 30 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 sacrum and coccyx lateral?
- Coccyx burnt out. Usual cause: sacral exposure. The fix: collimate and reduce mAs for the coccyx.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a sacrum and coccyx lateral in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.