Contributors: Justin Goggin, Patsy Whelehan
Species: Canine | Classification: Techniques
- 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 .
- Readily available.
- Dependent upon the method of chemical restraint (GA or sedation).
- 10-15 min 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?
- 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.
- Radiographer or Veterinary Nurse/Technician carrying out radiography.
- 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.
- High output X-ray machine.
- Rare Earth high resolution screens.
- Automatic processing facilities.
- Film labelling system.
- X-ray film.
- Pharmaceuticals for chemical restraint.
- 1-2 competent people.
- 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.
Reasons for Treatment Failure
- 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.