Contributors: Patsy Whelehan

 Species: Feline   |   Classification: Techniques

Introduction Requirements Preparation Procedure Aftercare Outcomes Further Reading

Introduction

  • 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.

Uses

Advantages

  • Non-invasive.
  • Straightforward.

Time Required

Preparation

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

Procedure

  • 10 to 15 minutes, or longer, dependent upon skill of radiographer.

Decision Taking

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
  • Standard projection.
  • 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.
  • 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.

Requirements

Personnel

Other involvement

  • Radiographer, or Technician carrying out radiography.

Materials Required

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.

Preparation

Restraint

  • One to two competent people.
  • Sandbags.
  • Foam wedges.
  • Tying tapes.
  • Positioning troughs.

Procedure

Core Procedure

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.

Aftercare

Outcomes

Reasons for Treatment Failure

Poor techinique

  • 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.

Other

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

Further Reading

Publications

Refereed papers

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