Lateral knee X-ray positioning
One of the routine knee views. The patient lies on their side, the beam passes from side to side, straight on to the receptor, and the centring point is the medial femoral condyle.
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
Lateral recumbent. On the side examined, the knee bent about 20–30°, a pad under the ankle; the other leg bent further forward.
Centring & collimation
Central ray
lateralCentre: the medial femoral condyle.
Beam: lateral, perpendicular to the receptor.
Collimate: the joint with a quarter of femur and tibia
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 | 1.6 | 0.8 |
| S | 53 | 2.5 | 1.25 |
| M | 53 | 3.2 | 1.6 |
| L | 53 | 5 | 2.5 |
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
- The femoral condyles are superimposed.
- The patellofemoral joint is open.
- 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 |
|---|---|---|
| Condyles separate | Leg rotated or ankle low | Pad the ankle; square the knee. |
Common questions
- Where do you centre for a knee lateral X-ray?
- The centring point is the medial femoral condyle.
- What distance and beam angle does a knee 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 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 a knee lateral?
- Condyles separate. Usual cause: leg rotated or ankle low. The fix: pad the ankle; square the knee.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a knee lateral in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.