Radiography: stifle

• 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 .

Advantages

• Non-invasive.
• Straightforward.

Preparation

• Dependent upon the method of chemical restraint (GA or sedation).

Procedure

• 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

Lateral

• Good for demonstrating joint effusion.
• Usually enables detection of fractures.
• May detect neoplastic conditions.

Craniocaudal

• 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.

Other involvement

• Radiographer, or Technician carrying out radiography.

Minimum equipment

• X-ray machine.
• Cassettes with high definition screens.
• Processing facilities.
• Immobilization and positioning aids: sandbags, foam wedges, tying tapes.
• Protective clothing (lead-rubber aprons).

Ideal equipment

• High output X-ray machine.
• Rare earth screens.
• Automatic processing facilities.

Minimum consumables

• X-ray film.
• Pharmaceuticals for chemical restraint.

• One to two competent people.
• Sandbags.
• 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.

• Inadequate sedation.
• Poor processing.
• Equipment failure.

Poor techinique

• 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.

Refereed papers

• Recent references from PubMed and VetMedResource.
• Allan G S (2000) Radiographic features of feline joint disease. Vet Clin North Am Small Anim Pract 30 (2), 281-302 PubMed.