Contributors: Patsy Whelehan
Species: Feline | Classification: Techniques
- A high definition film-screen combination is required.
- The soft tissues surrounding the joint should be included.
- General anesthesia or heavy sedation is required.
- The film should be correctly exposed and developed, and free from movement blur and artifact.
- The anatomical marker must be clearly visible, along with the patient's identification, the date, and the name of the hospital or practice.
- Joint effusion or soft tissue swelling .
- Fracture Fracture: overview (distal femur, proximal tibia, patella).
- Investigation of soft tissue injury.
- Soft tissue neoplasia invading bone Spinal neoplasia .
- Neoplastic bone disease .
- Dependent upon the method of chemical restraint (GA or sedation).
- 10 to 15 minutes, or longer, dependent upon skill of radiographer.
Criteria for choosing test
Is the examination appropriate?
- Can you make the diagnosis without it?
- Can it tell you what you need to know?
- Will your management be affected by the radiological findings?
Choosing the right projections
- Good for demonstrating joint effusion.
- Usually enables detection of fractures.
- May detect neoplastic conditions.
- Essential to have the second view where fracture is suspected or to assess fracture fully.
- Necessary for full assessment of neoplastic conditions.
Caudocranial (alternative to craniocaudal)
- This is arguably preferable to a craniocaudal projection as the stifle does not extend to a full 180 degrees. The beam geometry (oblique rays) will help to achieve a good projection through the joint and of the proximal tibia only when the beam is directed from the caudal aspect.
- The caudocranial is definitely preferable where there is abnormal restriction of stifle extension.
- The position can be tricky to achieve and is normally only possible with good chemical restraint.
- In extreme cases of positioning difficulty the caudocranial projection can be carried out with a horizontal beam.
- Radiographer, or Technician carrying out radiography.
- X-ray machine.
- Cassettes with high definition screens.
- Processing facilities.
- Immobilization and positioning aids: sandbags, foam wedges, tying tapes.
- Protective clothing (lead-rubber aprons).
- High output X-ray machine.
- Rare earth screens.
- Automatic processing facilities.
- X-ray film.
- Pharmaceuticals for chemical restraint.
- One to two competent people.
- Foam wedges.
- Tying tapes.
- Positioning trough.
Step 1 - Lateral
- Position the patient in lateral recumbency on the side to be examined and immobilize.
- Extend the contralateral limb as far caudally as possible and secure .
- Flex the hip slightly.
- Flex the stifle to about 90 degrees.
- Use padding under the hip and the distal limb as necessary to achieve a true lateral position of the joint with both the femur and the tibia/fibula parallel to the film.
- Center the vertical beam through the joint space which can be directly palpated .
- Collimate to include the distal third of femur, proximal third of tibia/fibula, and the soft tissues surrounding the joint .
Step 2 - Craniocaudal
- Position the patient in dorsal recumbency in a trough.
- Rotate slightly away from the affected side and immobilize .
- Extend the affected limb caudally and secure with a tie.
- Further adjust the position of the trunk to ensure that the stifle is in a true craniocaudal position.
- Check this position by ensuring that the patella is overlying the center of the distal femur.
If the stifle is not optimally extended, opt for a caudocranial projection.
- Center the beam through the joint in the mid-line .
- Collimate to include distal femur, proximal tibia/fibula, and the soft tissues surrounding the joint .
Step 3 - Caudocranial
- Position the patient in sternal recumbency.
- With the patient's pelvis elevated from the table top gently extend the affected limb until it is stretched out caudally.
- Place a pad between the stifle and the film to facilitate positioning and improve patient comfort.
- Flex and elevate the contralateral limb to rotate the pelvis and bring the affected limb into the true caudocranial position.
- Sandbags against the trunk on the same side as the limb under examination will assist in effective immobilization.
This is a difficult position to achieve and maintain. Excellent patient compliance is required, either through anesthesia or heavy sedation.
- Center with a vertical beam through the joint space.
- Collimate to include distal femur, proximal tibia/fibula and the structures surrounding the joint.
Step 4 - Caudocranial with horizontal beam
- The patient is positioned in lateral recumbency on the side opposite the affected limb.
- The affected limb is separated from the other and is supported on foam pads in a horizontal position with the stifle extended as much as possible.
- The film is positioned vertically in contact with the cranial aspect of the stifle and supported by a film holder or sandbags.
- The horizontal beam is directed through the joint space.
Radiation safety must not be compromized where a horizontal beam is used. Care must be taken to ensure that personnel are not in the path of the primary beam, and close collimation is essential.
Reasons for Treatment Failure
- Inadequate sedation.
- Poor processing.
- Equipment failure.
- Rotation of the joint away from the true lateral or true craniocaudal/caudocranial projections is probably the most common positioning failure.
- In the lateral, the two femoral condyles should overlie each other. If they are separated then the likelihood is that either the femur or the tibia/fibula is not parallel to the film.
- In the craniocaudal/caudocranial the patella should be centrally projected over the distal femur. It is important to check this prior to exposure by palpating carefully and to ensure that immobilization is effective.