Radiography: stifle

• A high resolution 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 artefact.
• The anatomical marker must be clearly visible, along with the patient's identification, the date, and the name of the hospital or practice.
• A grid is rarely necessary (only if patient thickness >10 cm).

• → Joint effusion or soft tissue swelling  , from traumatic infections or immune-mediated arthrosis.
• → Osteochondrosis Stifle: osteochondrosis .
• → Fracture (distal femur, proximal tibia  , patella  ).
• → Investigation of soft tissue injury.
• → Patellar luxation .
• → Neoplastic bone disease Bone: neoplasia .
• → Soft tissue neoplasia invading bone Synovial cell sarcoma .

Advantages

• Non-invasive.
• Readily available.

Preparation

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

Procedure

• 10-15 min or longer, dependent upon skill of radiographer.

Criteria for choosing test

• 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?

• Essential as part of a two view study for detection and characterization of pathology.
• Good for demonstrating joint effusion.

• Essential to have the second orthogonal view for complete radiographic study of any region.

• This is arguably preferable to a craniocaudal projection as the stifle does not extend to a full 180°. 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.
• This position brings the bones closer to the film, thus reducing geometric distortion.
• 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 Veterinary Nurse/Technician carrying out radiography.

Minimum equipment

• X-ray machine.
• Cassettes with high resolution screens.
• Processing facilities.
• Immobilization and positioning aids: sandbags, foam wedges, cloth tape or rope.
• Protective clothing (lead-rubber aprons), gloves, thyroid shields.
• Film labeling system.

Ideal equipment

• High output X-ray machine.
• Rare Earth high resolution screens.
• Automatic processing facilities.

Minimum consumables

• Film labelling system.
• X-ray film.
• Pharmaceuticals for chemical restraint.

• 1-2 competent people.
• Sandbags.
• Foam wedges.
• Cloth tape or rope.
• 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 .
• It will often be necessary to tie a tape around the dog's abdomen to keep the os penis or, in a bitch, the fat and mammary tissue from overlying the stifle .
• Flex the hip slightly.
• Flex the stifle to about 90degrees.
• 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 dog's pelvis elevated from the table top with a sand bag or foam pad, gently extend the affected limb until it is stretched out caudally.
• Place a thin foam 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 compromised 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.

• Incomplete study (failure to get two orthogonal views).
• Inadequate sedation.
• Poor processing.
• Equipment failure.
• Failure to properly label film.

• 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.