Knee tunnel view X-ray positioning (intercondylar)
An extra knee view, used when a routine one is not enough. The patient lies on their back, the beam passes front to back (AP), tilted 30° towards the feet, 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. Supine with the knee flexed over a detector on a firm 12–15 cm support.
Centring & collimation
Central ray
APCentre: the knee joint.
Beam: AP, angled 30° caudad.
Collimate: the intercondylar fossa
Distance, receptor & grid
| Setting | Value | Notes |
|---|---|---|
| SID | 100 cm | |
| Receptor | 18 × 24 cm | landscape |
| Placement | On a raised support | No grid |
| Angulation | 30° | caudad |
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 | 1.25 | 0.5 |
| S | 53 | 2 | 0.8 |
| M | 53 | 2.5 | 1 |
| L | 53 | 4 | 1.6 |
These start from a classic film-screen chart (53 kV, 32 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 intercondylar fossa is shown 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 |
|---|---|---|
| Fossa closed | Angle not perpendicular to the tibia | Adjust the angle. |
Common questions
- Where do you centre for a knee intercondylar (tunnel) X-ray?
- The centring point is the knee joint.
- What distance and beam angle does a knee intercondylar (tunnel) need?
- 100 cm from the tube to the receptor. The beam passes front to back (AP), tilted 30° towards the feet.
- 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 knee intercondylar (tunnel)?
- Fossa closed. Usual cause: angle not perpendicular to the tibia. The fix: adjust the angle.
Try it in ScanFlo: the ScanFlo XR X-ray Room, coming soon, lets you set up a knee intercondylar (tunnel) in a 3D room and score your positioning. See ScanFlo XR →
Written by the ScanFlo team from everyday radiographic practice.