Contributors: Patsy Whelehan
Species: Feline | Classification: Techniques
- A high definition film-screen combination is required.
- A grid is not required.
- kV should not exceed about 50.
- Both the stifle and the hock should be included.
- General anesthesia or 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.
- Fracture Fracture: overview .
- Angular limb deformity.
- 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
- Standard projection.
- Usually enables detection of fractures.
- May detect neoplastic conditions.
- Essential to have the second view where fracture is suspected or to assess fracture fully.
- Essential for assessing angular limb deformity.
- Necessary for full assessment of neoplastic conditions.
Caudocranial (alternative to craniocaudal)
- This is arguably preferable to a craniocaudal projection as the tibia will lie more horizontal and distortion of the image will therefore be more easily avoided.
- 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 troughs.
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 foot as necessary to achieve a true lateral position of the tibia/fibula, parallel to the film.
- Center the vertical beam at mid-shaft.
- Collimate to include both the stifle and the hock .
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.
For angular limb deformity it may be advisable to avoid excessive immobilization of the foot. Position from the stifle and let the limb lie as naturally as possible.
- Further adjust the position of the trunk to ensure that the tibia/fibula is in a true craniocaudal position.
If the stifle is not optimally extended, opt for a caudocranial projection.
- If necessary, tilt the beam and the film to correspond to any angulation of the tibial shaft.
- Collimate to include the stifle and the hock, along with the soft tissues surrounding the bone .
Step 3 - Caudocranial
- Postion 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.
- Extend the hock.
- 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 at mid-shaft.
- Collimate to include stifle and hock and the soft tissues surrounding the bone .
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 tibia/fibula and supported by a film holder or sandbags.
- The horizontal beam is through the middle of the shaft.
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
- Rotation due to lack of care when positioning or movement of patient between positioning and exposure.
- Distortion (foreshortening) due to the beam not being perpendicular to the shaft and the film not being parallel to the bone.
- Inadequate sedation.
- Poor processing.
- Equipment failure.