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Radiographic technique

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Hip Radiographs

 

Radiographs are obtained under sedation or anesthesia for several reasons:

■  To minimize stress to the patient;

■  To permit precise positioning of the pelvis and hips;

■  To remove the need for the animal to be held, as x-rays are potentially hazardous for anyone doing so.

 

The radiographic view required by the BVA/KC scoring scheme, as for most other hip dysplasia schemes, is the extended ventrodorsal (VD) view . The dog is positioned on its back with its hindlegs extended caudally, resulting in a position similar to that of a standing human. The femora must be positioned parallel to each other and for this the stifles are rotated slightly medially and held in position with a tie or tape so that they lie in the sagittal plane with the patella superimposed over the centre of the distal femur. This position allows the femoral neck to be seen clearly, without superimposition by the greater trochanter, and facilitates the detection of new bone on the femoral neck.

 

 

The extended VD position has several advantages:

■  It is easy and safe to achieve;

■  It is very repeatable;

■  It requires no special positioning aids;

■  It gives an excellent view of the hip joint in which all relevant anatomical areas can be seen.

 

Centring of the x-ray beam must be at the level of the hip joints, which can be achieved by palpation of bony landmarks such as the pubic symphysis and greater trochanters. Centring further cranially or further caudally will distort the appearance of the hip joints. Collimation must be sufficient to include the pelvis but it is not necessary to include the stifles; to do so requires either incorrect centring or an unacceptably large area to be irradiated.

 

It is important to avoid tilting the dog to the side (lateral rotation) as this will alter the appearance of the hips and may worsen the score, since the hip that is closer to the table may appear artefactually subluxated. It is also important that the technical quality of the image is of a high standard with optimum contrast and definition and all the necessary labelling. Radiographs that are poorly positioned or which are technically substandard may be rejected if the scrutineers feel that an accurate score cannot be given. Further details on radiography and submission are given in the BVA’s Guidance Notes for the hip dysplasia scheme.

 

 

 

Reference

 

DENNIS R. Interpretation and use of BVA/KC hip scores in dogs. In Practice. BMJ Publishing Group Limited; 2012 Apr 16;34:178–194.

 

 

 

Elbow Radiographs

Medio-Lateral projection (extended)

Patient preparation: No special preparation is required.

Patient positioning: Place the patient in lateral recumbency with the affected limb next to the tabletop. Forcefully pull the limb downward and cranially and position the limb so that the elbow joint is in a 120° extended position. Use sandbags to hold the limb in position. Arch the head and neck dorsally using sandbags to hold the position. Pull the unaffected leg caudally and hold it with sandbags or tie to the tabletop. Sandbags can be used to hold the pelvic limbs.

X-ray beam direction: The vertically directed x-ray beam is centered on the elbow joint.

Comments: If the lateral view of the elbow joint is made with the limb in partial extension of a specific angle, it is relatively easy to repeat that positioning on subsequent studies. With the elbow joint positioned in full extension, rotation of the limb into a position of supination is common and this alters the way the bones are seen on the radiograph.

 

Medio-Lateral projection (Flexed)

Patient preparation: No special preparation is required.

Patient positioning: Place the patient in lateral recumbency with the affected leg next to the tabletop. Position the limb so that the elbow joint is in 90° flexion. Use sandbags to hold the limb in position. Arch the head and neck dorsally using sandbags to hold the position. Pull the unaffected leg caudally and hold it with sandbags or tie to the tabletop. Sandbags can be used to hold the pelvic limbs.

X-ray beam direction: The vertically directed x-ray beam is centered on the elbow joint.

Comments: If the lateral flexed view of the elbow joint is made with the limb flexed at 90° , evaluation of the anconeal process of the ulna is possible. It is relatively easy to repeat this positioning on subsequent studies.

 

Cranio-caudal projection

Patient preparation: No special preparation is required

Patient positioning: The patient is placed in sternal recumbency with the forelimb to be studied pulled as far cranially as possible and held by sandbags or tied to the table. The opposite forelimb can be left in a neutral position. Hyperextend the dog's neck and pull the head laterally toward the unaffected limb so that it is not within the primary beam. This positioning places the radius and ulna parallel to the tabletop but the humerus remains at an angle to the tabletop.

X-ray beam direction: The vertically directed beam is angled distoproximally 10to 20in an effort to display the joint surfaces better.

 

Cranial 25-degree lateral-caudomedial oblique projection.

This projection can also be obtained to highlight the medial coronoid region and fragmented coronoid process.

Patient preparation: No special preparation is required.

Patient positioning: The patient is placed in sternal recumbency with the forelimb to be studied pulled as far cranially as possible and held by sandbags or tied to the table. Rotate the patient approximately 25° medially.  The dog's head can be positioned laterally toward the unaffected limb so that it is not within the primary beam for both oblique views. The opposite forelimb can be left in a neutral position.

X-ray beam direction: The vertically directed beam is perpendicular to the tabletop for the oblique views.