Radiography: carpus and forefoot

• A high resolution film-screen combination is required.
• A grid is not required.
• In UK, 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 artefact.
• The anatomical marker must be clearly visible, along with the patient's identification, the date, and the name of the hospital or practice.

• Fracture .
• Dislocation.
• Neoplasia: bony Bone: neoplasia , or soft tissue invading bone Synovial cell sarcoma.
• Carpal valgus/varus but full length radius and ulna views including the carpus may be preferable.
• Foreign bodies.
• Arthritis .
• Infection.

Advantages

• Non-invasive.
• Easily performed clinical practice.

Preparation

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

Procedure

• 10-15 min or longer, dependent upon skill of radiographer.

Criteria for choosing test

• 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?

• Standard projection Radiographic positioning video: distal limb - spread toe view.
• 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.

• 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 and characterize fractures.

• Supplementary views.
• Can be important in the carpus for more complete evaluation of complex joints.
• 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.

• Supplementary views.
• Useful for confirming or assessing extent of carpal instability.
  Make sure this is undertaken without compromising radiation safety and be sure that you are not going to make the condition of the patient worse.

Other involvement

• Radiographer or veterinary nurse/technician carrying out radiography.

Minimum equipment

• X-ray machine.
• X-ray cassettes.
• Processing facilities.
• Immobilization and positioning aids: sandbags, foam wedges, clothtape or rope.
• Protective clothing (lead-rubber aprons), gloves, thyroid shields.
• Film labelling system.

Ideal equipment

• High output X-ray machine.
• Rare earth high resolution screens.
• Automatic processing facilities.
• Film ID camera.
  When looking for subtle abnormalities in very small dogs, it can be helpful to use non-screen dental film or a cassette designed for human mammography. This is a very high detail, high latitude system, with only one screen in the cassette utilizing single-sided emulsion film. It naturally requires higher mAs values than twin-screen systems.

Minimum consumables

• X-ray film.
• Pharmaceuticals for chemical restraint.
• Film label or tape.

• 1-2 competent people.
• Sandbags.
• Foam wedges.
• Cloth tape or rope.
• Adhesive tape.

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° foam wedge against the palmar aspect of the carpus and foot.
• Place a sandbag on the foam wedge to hold it and the foot in position.
• 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 film 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.
  Have the hindlimbs both positioned to the side opposite the forelimb under examination.
• Place a 15° 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 .

Step 3 - Obliques

• These are probably best based on the dorsopalmar position .

• 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° foam wedge, backed by a sandbag, against the palmar aspect.

• 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° foam wedge, backed by a sandbag, against the palmar aspect.
  It may be necessary to support the patient with sandbags next to the thorax.

Step 4 - Stressed views of the carpus

• 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 compromising 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.

• 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.

• Inadequate sedation.
• Poor technique: inaccurate positioning or centring/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.
• Failure to label film.
• Equipment failure.
• Incomplete study (at least two views are needed).

Refereed papers

• Recent references from PubMed and VetMedResource.
• Bradley K (2005) Radiography and radiology of the carpus and hock. UK Vet 10 (5), 39-42.