Contributors: Justin Goggin, Patsy Whelehan
Species: Canine | Classification: Techniques
- A high detail film-screen combination is required.
- Soft tissues should be included.
- kV should not exceed 50 in UK.
- General anesthesia or sedation is advised.
- 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 .
- Osteochondrosis Hock: osteochondrosis .
- Tarsal valgus/varus Distal tibia: angular deformity (but full length tibia/fibula views including the tarsus may be preferable).
- Neoplasia: bony Bone: neoplasia or soft tissue invading bone Synovial cell sarcoma.
- Investigation of joint effusion/swelling from trauma, immune-mediated or infectious arthritis.
- Foreign bodies.
- Common calcaneal tendon injury Hock: calcaneal tendon injury .
- Easily performed.
- Dependent upon the method of chemical restraint (GA or sedation).
- 10-15 min 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 want to know?
- Will your management be affected by the radiological findings?
Choosing the right projections
- Lateral and dorsoplantar views are the minimal two views necessary, but four views (lateral, dorsoplantar, dorsomedial-plantarlateral and dorsolateral-plantarmedial) are recommended for a complete study. Flexed lateral, stressed and 'skyline' dorsoplantar views are also valuable sometimes.
- Standard projection Radiographic positioning video: distal limb - spread toe view.
- Shows soft tissue swelling/joint effusion well.
- Can show fractures and displacement of metatarsals and phalanges, but obliques may be of more use.
- Standard projection .
- More use than the lateral in the foot, as metatarsals and phalanges are not overlying each other.
- Shows joint effusion/soft tissue swelling.
- Vital to have two views at right angles to localize pathology of all types.
Dorsolateral-plantaromedial oblique/dorsomedial-plantarolateral oblique
- Supplementary views.
- Important in the tarsus, because of the complex anatomy.
- 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 compromising radiation safety and be sure that you are not going to make the condition of the patient worse.
- Used to evaluate proximal/plantar portions of the trochlear ridges that are covered by fibula and tibia on standard lateral view.
'Skyline' dorsoplantar view
- Useful to rule out fracture or OCD fragments arising from the dorsal portions of the trochlear ridges.
- Radiographer or nurse/technician to carry out radiography.
- X-ray machine.
- Cassettes with high detail screens.
- Processing facilities.
- Immobilization and positioning aids: sandbags, foam wedges, cloth tape or rope.
- Film labeling system.
- Protective clothing (lead-rubber aprons).
- High output X-ray machine.
- Rare earth high detail screens.
- When looking for subtle abnormalities in very small dogs it can be helpful to use 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.
- Automatic processing facilities.
- Film ID camera and lead R, L, DMPLO and DLPMO labels.
- Positioning trough.
- X-ray film.
- Pharmaceuticals for chemical restraint.
- One to two competent people.
- Foam wedges.
- Ropes/tying tapes.
- Radiolucent adhesive tape.
- Positioning trough.
- Positioning blocks.
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° 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
- 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 compromising 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.
- The flexed lateral also profiles the plantar proximal aspects of the trochlea of the talus without overlap of the tibia and fibula.
- Take a radiograph with the foot pulled dorsally and one with the foot pulled to the plantar aspect.
Step 5 - 'Skyline' dorsoplantar view of the talus
- Place patient in dorsal recumbency.
- Extend rear leg and rest tarsus on a cassette resting on a square foam block, with the hock flexed.
- Collimate to include tibiotarsal joint (direct beam tangential from dorsal to plantar through joint).
Reasons for Treatment Failure
- 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.
- Incomplete study (two orthogonal views are essential if any abnormalities are visible on these views, obliques (DMPLO, DLPMO) and possibly stressed or 'skyline' views are recommended).
- Inadequate sedation.
- Wrong exposure factors.
- Poor processing.
- Equipment failure.
- Failure to label film properly/completely.