Lateral knee X-ray positioning (horizontal beam)
An extra knee view, used when a routine one is not enough. The patient lies on their back, the beam passes from side to side, straight on to the receptor with the tube horizontal, and the centring point is the knee joint.
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
Supine. Do not bend an injured knee. Detector vertical beside it, supported by a foam pad; raise the other leg.
Centring & collimation
Central ray
lateralCentre: the knee joint.
Beam: lateral, perpendicular to the receptor, horizontal beam.
Collimate: the joint
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | Horizontal beam |
| Receptor | 18 × 24 cm | portrait |
| Placement | Erect (wall) bucky | 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 | 1.6 | 0.63 |
| S | 53 | 2.5 | 1 |
| M | 53 | 3.2 | 1.25 |
| L | 53 | 5 | 2 |
These start from a classic film-screen chart (53 kV, 40 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
- A lipohaemarthrosis fluid level, if present, 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 |
|---|---|---|
| Knee bent | Standard lateral used after injury | Use the horizontal beam. |
Common questions
- Where do you centre for a knee lateral (horizontal beam) X-ray?
- The centring point is the knee joint.
- What distance and beam angle does a knee lateral (horizontal beam) need?
- 100 cm from the tube to the receptor. The beam passes from side to side, straight on to the receptor with the tube horizontal.
- What size receptor, and do you need a grid?
- Use an 18 × 24 cm receptor, portrait, in the wall bucky. 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 knee lateral (horizontal beam)?
- Knee bent. Usual cause: standard lateral used after injury. The fix: use the horizontal beam.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a knee lateral (horizontal beam) in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.