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

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 carpus, 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 metacarpals and phalanges, but obliques may be more useful.
Dorsopalmar
  • Standard projection.
  • More useful than the lateral in the foot, as metacarpals and phalanges are not overlying each other.
  • Important in the carpus 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-palmaromedial oblique/dorsomedial-palmarolateral oblique
  • Supplementary views.
  • Can be important in the carpus, for giving full information on fractures and dislocations.
  • Can be very useful in the foot for showing metacarpals and phalanges in a different plane from the dorsopalmar, but without as much overlapping as in the lateral.
Stressed views of the carpus - forced abduction or adduction, forced flexion or extension
  • Supplementary views.
  • Useful for confirming or assessing extent of carpal 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.
  • Protective clothing (lead-rubber aprons).

Ideal equipment

  • High output X-ray machine.
  • Rare earth high definition screens.
  • Automatic processing facilities.
    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.

Minimum consumables

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

Preparation

Restraint

  • One to two competent people.
  • Sandbags.
  • Foam wedges.
  • Tying tapes.
  • Adhesive tape not zinc oxide.

Procedure

Core Procedure

Step 1 - Lateral

  • Position the patient in lateral recumbency on the side to be examined and immobilize.
  • Use padding under the shoulder and elbow as necessary to ensure that the carpus and foot are in a lateral position.
  • Place the flat side of a 15 degree foam wedge against the palmar aspect of the carpus and foot.
  • Maintain an accurate position with adhesive tape.
  • Center with a vertical beam through the middle of the carpus if that is the area of interest, or over the metacarpus 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 - Dorsopalmar

  • Place the patient in sternal recumbency.
  • Extend the shoulder and elbow on the affected side .
    If the elbow and shoulder are not extended it is difficult to maintain an unrotated dorsopalmar position at the distal limb.
  • Place a 15 degree foam wedge under the elbow to facilitate achieving the correct orientation of the distal limb.
  • Sandbag the radius and ulna to keep the foot lying in the true dorsopalmar position. This is preferable to tying the foot but adhesive tape can be very useful to keep the foot still and to spread the toes.
  • Center with a vertical beam through the middle of the carpus if that is the area of interest, or more distally as required.
  • Collimate closely, including the whole area of interest with soft tissues   Forelimb: normal carpus and paw (skeletally immature) - radiograph DPa  .

Step 3 - Obliques

  • These are probably best based on the dorsopalmar position .
Dorsolateral-palmaromedial oblique
  • The limb is rotated medially by flexing, abducting and slightly elevating the elbow to give a dorsolateral-palmaromedial oblique.
  • The carpus and foot are supported in this position by placing a small 45 degree foam wedge, backed by a sandbag, against the palmar aspect.
    Adhesive tape may also be helpful.
Dorsomedial-palmarolateral oblique
  • The elbow is flexed and tucked in towards the thorax to rotate the limb laterally.
  • The carpus and foot are supported in this position by placing a small 45 degree foam wedge, backed by a sandbag, against the palmar aspect (use adhesive tape if necessary).
    It may be necessary to support the patient with sandbags next to the thorax.

Step 4 - Stressed views of the carpus

Forced abduction/adduction
  • Position as for standard dorsopalmar.
  • Carefully place one tie proximal and one tie distal to the joint to be stressed.
    In practice this usually means around the distal radius and ulna, and around the metacarpus.
  • 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 patient'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 radius and ulna, and around the metacarpus.
  • Take a radiograph with the foot pulled dorsally ie the carpus hyperextended.
  • If a hyperflexed view is also required, the tapes may not work as well. It may be better to flex the joint and then apply one band around the foot and the distal radius.

Aftercare

Outcomes

Reasons for Treatment Failure

  • Inadequate sedation.
  • Poor technique: inaccurate positioning or centering, wrong exposure factors.
  • The most common positioning problem is rotation of the carpus and foot away from either the true lateral or the true dorsopalmar position. To avoid this, it is important to position from the proximal end of the limb. If the elbow is right, the foot will lie as required. Liberal use of foam wedges and sandbags is important in successfully maintaining the positions.
  • 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.