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.
  • Soft tissues 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

  • Fracture Fracture: overview  Tarsus: chronic trauma - radiograph lateral .
  • Dislocation.
  • Neoplasia: bony , or soft tissue invading bone Synovial sarcoma .
  • Tarsal valgus/varus but full length tibia/fibula views including the tarsus may be preferable.
  • Investigation of joint effusion/swelling  Carpus: disease - radiograph DP  .
  • Foreign bodies.
  • Degenerative joint disease.
  • Achilles tendon injury.

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 want to know?
  • Will your management be affected by the radiological findings?

Choosing the right projections

Lateral
  • Standard projection.
  • Important for the tarsus, when looking for fractures or dislocation.
  • Shows soft tissue swelling/joint effusion.
  • Vital for localizing radio-opaque foreign bodies in the foot.
  • Can show fractures and displacement of metatarsals and phalanges, but obliques may be of more use.
Dorsoplantar
  • Standard projection.
  • More use than the lateral in the foot, as metatarsals and phalanges are not overlying each other.
  • Important in the tarsus for fractures and dislocations.
  • Shows joint effusion/soft tissue swelling.
  • Vital to have two views at right angles to localize radio-opaque foreign bodies in the foot.
Dorsolateral-plantaromedial oblique/dorsomedial-plantarolateral oblique
  • Supplementary views.
  • Can be important in the tarsus, for giving full information on fractures and dislocations.
  • Can be very useful in the foot for showing metatarsals and phalanges in a different plane from the dorsoplantar, but without as much overlapping as in the lateral.
Stressed views of the tarsus - forced abduction or adduction, forced flexion or extension
  • Supplementary views.
  • Useful for confirming or assessing extent of tarsal instability.
    Make sure this is undertaken without compromizing radiation safety and be sure that you are not going to make the condition of the patient worse.

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, radiolucent adhesive tape.
  • Protective clothing (lead-rubber aprons).

Ideal equipment

  • High output X-ray machine.
  • Rare earth high definition screens.
  • When looking for subtle abnormalities it can be helpful to use dental film, or a cassette designed for human mammography.
  • This is a very high definition, high contrast system with only one screen in the cassette, utilizing single-sided emulsion film. It has been quite widely used in equine radiography, but it should be remembered that it is designed for use at very low kV values (around 30kV) and optimum perfomance will be achieved around this level. It naturally requires higher mAs values than twin-screen systems.
  • Automatic processing facilities.
  • Positioning trough.

Minimum consumables

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

Preparation

Restraint

  • One to two competent people.
  • Sandbags.
  • Foam wedges.
  • Tying tapes.
  • Radiolucent adhesive tape.
  • Positioning trough.
  • Positioning block.

Procedure

Core Procedure

Step 1 - Lateral

  • Position the patient in lateral recumbency on the side to be examined and immobilize.
  • Secure the contralateral limb out of the field.
  • Use padding under the proximal limb as necessary to ensure that the tarsus and foot are in a lateral position.
  • Immobilize the limb.
  • Center with a vertical beam through the middle of the tarsus if that is the area of interest, or over the metatarsus if the foot is required .
    Remember, the oblique rays will make joint spaces towards the periphery of the field appear narrower, so center accurately for the area of interest.
  • Collimate closely, including the area of interest with soft tissues .

Step 2 - Dorsoplantar

  • Place the patient in dorsal recumbency in a trough.
  • Rotate the body slightly away from the affected side.
  • Extend the hip and stifle on the affected side.
    It can be difficult to make the hock and foot lie flat. Try varying the degree of stifle extension and elevate the foot and cassette on blocks or pads, possibly angled up distally.
  • Sandbags can often most usefully be placed over the femur to maintain the correct degree of stifle extension and therefore hold the foot on the cassette.
  • When concentrating on the tarsus, use a tie to secure the foot in position.
  • When interested more in the foot, adhesive tape is preferable.
  • Ensure that a true dorsoplantar position is achieved by rotating the whole leg, not by twisting the foot.
  • Center with a vertical beam through the middle of the tarsus if that is the area of interest, or more distally as required .
  • Collimate closely, including the whole area of interest with soft tissues .

Step 3 - Obliques

  • These are probably best based on the dorsoplantar position.
Dorsolateral plantaromedial oblique
  • Rotate the stifle, and possibly the body, further away from the affected side to elevate the lateral aspect of the foot.
  • Place a 45 degree pad under the plantar aspect of the foot and secure in position.
Dorsomedial plantarolateral oblique
  • Rotate the leg towards the lateral aspect to raise the medial aspect of the foot from the cassette.
  • Pad and secure.

Step 4 - Stressed views of the tarsus

Forced abduction/adduction
  • Position as for standard dorsoplantar.
  • Carefully place one tie proximal and one tie distal to the joint to be stressed. In practice this usually means around the distal tibia/fibula, and around the metatarsus.
  • Take two views, one with the proximal tie pulling laterally and the distal tie pulling medially, and the other with these reversed.
    To avoid compromizing radiation safety, these ties should be held taut by sandbags, rather than by hand, but for the dog's sake, this must be done in a carefully controlled fashion.
Forced flexion and extension
  • Position as for a standard lateral.
  • Place ties carefully proximal and distal to the joint to be stressed. In practice, this usually means around the distal tibia/fibula, and around the metatarsus.
  • Take a radiograph with the foot pulled dorsally and one with the foot pulled to the plantar aspect.

Aftercare

Outcomes

Reasons for Treatment Failure

Poor positioning

  • The most common positioning problem is rotation away from the true dorsoplantar projection. It is important to ensure that the body and proximal limb are in the right position, otherwise the distal limb will be pulled round.
  • The limb must be well supported and the foot immobilized as thoroughly as possible.

Other

  • Inadequate sedation.
  • Wrong exposure factors.
  • Poor processing.
  • Equipment failure.

Further Reading

Publications

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.