Contributors: Patsy Whelehan
Species: Feline | Classification: Techniques
- Attention to detail in radiographing the pelvis is important, as high standards of positioning are vital for accurate radiological assessment.
- A good supply of the appropriate positioning aids is needed.
- It is particularly important that the patient is highly compliant. General Anesthesia or heavy sedation with analgesia is required.
- The image should include the whole pelvis, the proximal femora, and the soft tissues surrounding the femora, as any muscle wastage should be noted.
- The film should be checked for correct positioning, exposure and processing and should be 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.
- Fractures of the pelvis Fracture: overview .
- Fractures of the proximal femur .
- Dislocation of the coxofemoral joint (compare with normal ).
- Neoplastic disease.
- Hip dysplasia (occasionally seen) Hip: dysplasia.
- Dependent upon method of chemical restraint: (General Anesthetic or sedation.)
- 10-15 mins, or longer, dependent upon skill of radiographer.
If possible, the patient should be left in position while the film is processed so that any inaccuracies in the projection can be corrected from the original position.
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
- The standard and most useful projection.
- Enables detection of most fractures and assessment of the coxofemoral joints.
- Shows direction of displacement in hip dislocation.
- Necessary for assessment of fracture displacement.
- Not suitable for assessing the femoral head and neck.
Lateral of one hip
- Important for assessing fractures or neoplasia involving the femoral head and neck.
- Radiographer / Veterinary Technician carrying out radiography.
- X-ray machine.
- Cassettes with high definition screens.
- Processing facilities.
- Immobilization and positioning aids: sandbags, foam wedges, tying tapes, medical adhesive tape (not zinc oxide).
- Protective clothing (lead-rubber aprons).
- High output X-ray machine.
- Rare earth screens.
- Automatic processing facilities.
- Hooks on the end of the X-ray table for attaching tapes used to extend legs.
- X-ray film.
- Pharmaceuticals for chemical restraint.
- Usually two competent people.
- Foam wedges.
- Tying tapes.
- Positioning trough.
- Medical adhesive tape (not zinc oxide).
Step 1 - Ventrodorsal
- Place the patient in dorsal recumbency, thorax in a positioning trough.
- Immobilize with a long sandbag caudal to the elbows.
- Foam wedges or small sandbags between the thorax and the sides of the trough may be helpful to prevent rotation.
- Make sure that the thorax is not rotated to the side as this would make it more difficult to keep the pelvis straight.
- Place a tie around each hindlimb above the hocks.
- Draw the hindlimbs caudally to maximum extension of the hips and stifles and secure the ties, to the table if possible, otherwise to sandbags.
- Rotate the hindlimbs medially until the femora are parallel to each other and the stifles are in a true craniocaudal position.
- Secure the femora in this position by tying a tape around them or, more conveniently, by using adhesive tape wrapped round a number of times. The tape used should not be too sticky and should be easy to tear across for removal.
- Stand at the caudal end of the table and place the hands under the pelvis.
- Palpate the tubercle on the dorsal aspect of each ilium and rotate the pelvis until these are equidistant from the film.
A lightweight long sandbag placed across the hocks (supported from the underneath if necessary), will further help to prevent rotation.
- Center with a vertical beam in the mid-line at the level of the symphysis pubis.
- Collimate to include the wings of ilium and a good portion of the femora .
It is not necessary to include the stifles.
- Include the femoral musculature in the beam.
If possible, prevent any movement of the patient until the radiograph has been processed and checked.
Step 2 - Lateral pelvis
- Place the patient in lateral recumbency on the X-ray table and immobilize with sandbags.
- It is not critical on which side the patient lies but it is wise to follow the principle of placing the side of interest nearer the film unless this would result in undue pain to the patient.
- To achieve a true lateral position of the pelvis, palpate the tubercles on the dorsal ilium and ensure that these are lying one above the other.
- Use foam wedges under the lower femur and between the femora to maintain the true lateral position.
- The hindlimbs do not need to be drawn unnaturally caudally.
- Center with a vertical beam over the femoral head.
- Collimate to include the entire pelvis.
Step 3 - Lateral single hip
- This position is most easily achieved from the ventrodorsal position with the patient's thorax placed in a trough and tilted towards the side under examination.
- Immobilize the patient with a long sandbag caudal to the elbows.
- Use a combination of ties and sandbags to abduct the unaffected limb.
- Flex the affected hip and stifle and elevate the distal limb with foam wedges in order to bring the femur parallel and lateral to the film.
- Center with a vertical beam through the hip joint .
- Collimate to include the whole of the joint with the proximal third of the femur.
Step 1 - Assessing film quality and correcting rotation
- In the case of a ventrodorsal radiograph showing a rotated projection, it is important to know how to recognize and correct this.
- Compare the size of the obturator foramina.
- If one foramen appears SMALLER, this side of the pelvis is rotated TOWARDS the film .
- Alternatively, or additionally, compare the apparent width of the wings of ilium.
- If one side appears WIDER this side is rotated TOWARDS the film.
When correcting this on the patient, be reasonably positive - move the bones, not just the soft tissues.
Reasons for Treatment Failure
- Inadequate sedation.
- Poor processing.
- Equipment failure.
- The most common problem is rotation of the pelvis when carrying out the ventrodorsal view.
- To avoid rotation it is necessary to palpate the pelvis as well as looking at the patient.
- Using only a visual check can be inaccurate due to asymmetry of the soft tissues or optical illusions caused by coat markings.
- Remember to consider the whole animal when positioning.
If the thorax is rotated then it will be very difficult to obtain a straight pelvis.