A good knowledge of anatomy is essential to identify correct centring and collimation points so the whole area of interest is included on a single radiograph. As a number of different views are used when radiographing limbs it is important to understand anatomical direction terminology used to describe the various views.

A radiograph is a two-dimensional image of a three-dimensional structure, this is why two orthogonal views should always be taken. It is recommended the opposite limb is also radiographed to enable comparison.

A variety of positioning aids should be available to assist in positioning your patient. Lead sheets can also be useful so that two exposures can be taken on a single cassette. A variety of cassette sizes containing both fast and detailed screen-film combinations should be available.

Heavy sedation or general anaesthesia is necessary to facilitate limb positioning.

When radiographing the limbs it is particularly important to ensure the coat is clean, dry and mud-free.

Shoulder

Mediolateral View

The patient is positioned in lateral recumbency with the limb of interest closest to the cassette. This limb is extended and secured in a cranioventral direction. The uppermost limb is retracted caudally and the neck extended.

Caudocranial View (CdCr)

The patient is positioned in dorsal recumbency with the thorax slightly rotated away from the shoulder joint. The limb is extended.

Centring and Collimation for Both Views

 Centring: Over the joint space located by palpation.

 Collimation: To include the distal third of the scapula and proximal third humerus.

Cranioproximal-Craniodistal Oblique (CrPr-CrDiO)

This view isn't routinely performed, but can give information on new bone formation or calcification within the supraspinatus or biceps tendon within the intertubercular groove.

Elbow

Mediolateral View

The patient is positioned in lateral recumbency with the uppermost limb drawn caudally and the neck extended.

 Flexed view: Limb flexed towards the neck and secured. Carpus and elbow joints should remain in lateral position.

 Extended view: Limb is fully extended and secured.

A small foam wedge under the olecranon can maintain the elbow in a true lateral position.

Craniocaudal View (CrCd)

The patient is positioned in sternal recumbency with head elevated and turned away from the limb of interest. Slightly rotating the thorax can bring the elbow into a CrCd position. The limb of interest is extended cranially.

Centring and Collimation for Both Views

 Centring: Over medial epicondyle humerus.

 Collimation: To include distal third humerus and proximal third radius/ulna (antebrachium).

Requirements for the BVA/KC Elbow and Hip Dysplasia schemes will be discussed in the lecture.

Carpus

Mediolateral View

The patient is positioned as for lateral elbow with uppermost limb drawn caudally.

Dorsopalmar (DPa)

The patient is positioned as for CrCd elbow. A foam wedge underneath the elbow can reduce rotation.

Centring and Collimation for Both Views

 Centring: Over the carpal joint.

 Collimation: To include distal third antebrachium and proximal metacarpals.

Scapula

Mediolateral View

There are two ways to position for a lateral scapula. For both methods the patient is positioned in lateral recumbency.

 Method 1. The limb being examined is pushed dorsally towards the spine so the scapula protrudes above the vertebrae. The uppermost limb is pulled and secured ventrally to rotate the thorax. The scapula can be palpated above the spine.

 Centring: Over central body scapula.

 Collimation: To include acromion, dorsal border of scapula and shoulder joint.

 Method 2. The limb being examined is pulled in a caudal ventral direction with the uppermost limb extended and secured cranially. A foam wedge underneath the sternum rotates the thorax.

 Centring: Over central body scapula.

 Collimation: To include dorsal border scapula and shoulder joint.

Method 2 is recommended for patients with suspected fractures.

Caudocranial View (CdCr)

The patient is positioned as for the CdCr shoulder.

 Centring: Over the central body scapula.

 Collimation: To include dorsal border scapula, shoulder joint and lateral skin surface.

Humerus

Mediolateral View

The patient is positioned in lateral recumbency with limb of interest closest to cassette. The limb being examined is extended and secured in a cranioventral direction. The uppermost limb is retracted in a caudodorsal direction and the neck extended.

Caudocranial View (CdCr)

The patient is positioned as for the CdCr shoulder view. The limb being examined is extended cranially alongside the skull to bring the humerus as parallel to the cassette as possible.

Centring and Collimation for Both Views

 Centring: Mid-humerus.

 Collimation: To include shoulder and elbow joints.

Radius/Ulna

Mediolateral View

The patient is positioned as for lateral elbow. A foam wedge underneath the carpus can help position the antebrachium parallel to the cassette.

Craniocaudal View (CrCd)

The patient is positioned as for the CrCd elbow view.

Centring and Collimation for Both Views

 Centring: Mid-antebrachium.

 Collimation: To include elbow and carpal joints.

Pelvis

Mediolateral View

The patient is positioned in lateral recumbency with the hindlimbs in a natural position and femurs parallel. A foam wedge placed between the femurs helps to keep them parallel, and one under the sternum can reduce axial rotation.

 Centring: Over greater trochanter of femur.

 Collimation: To include wings of ilia, ischium and proximal third femur.

Ventrodorsal View (VD)

The patient is positioned in dorsal recumbency with the hindlimbs extended caudally and secured at hock with ties. Both femurs are rotated medially and secured at the stifles with tape or ties so the femurs are parallel and patellae central over the femoral trochleae. On palpation the wings of ilia should be equidistant to tabletop.

 Centring: On midline at the level of greater trochanter.

 Collimation: To include wings of ilia, stifles and lateral skin surfaces.

If clinically possible do not move the patient until the radiograph has been viewed so that any small positioning adjustments can be made.

Stifle

Mediolateral View

The patient is positioned in lateral recumbency. The uppermost limb is abducted and secured and the limb of interest slightly flexed into neutral position. A foam wedge underneath the hock can bring the tibia parallel to the cassette so the femoral condyles are superimposed.

Caudocranial View (CdCr)

The patient is positioned in sternal recumbency with limb of interest extended caudally. A foam wedge under the stifle can facilitate positioning. The opposite limb is flexed and abducted onto a foam wedge to rotate the patient onto the opposite limb. The patella should be central to the femoral condyles.

Centring and Collimation for Both Views

 Centring: Over stifle joint.

 Collimation: To include distal third femur and proximal third tibia.

Tibial Plateau Levelling Osteotomy Views

When taking radiographs for tibial plateau levelling osteotomy (TPLO) assessment the hock must be included within the collimated area on both radiographs. On the lateral view the hock and femur should be at 90 degrees to the tibia.

Tarsus / Hock

Mediolateral View

The patient is positioned in lateral recumbency with limb of interest closest to cassette and flexed slightly into a natural position. A foam wedge under the stifle can reduce rotation. The uppermost limb is extended cranially and secured.

Plantarodorsal View (PlD)

The plantarodorsal is preferable to the dorsoplantar view as the fibular tarsal bones align with the tibia rather than lie obliquely across the joint. The patient is positioned as for CdCr stifle.

Centring and Collimation for Both Views

 Centring: Mid-tarsal joint.

 Collimation: To include distal third tibia and proximal third metatarsals.

Femur

Mediolateral View

The patient is positioned in lateral recumbency, but the body rotated approximately 45 degrees into dorsal whilst the pelvis remains rotated. The stifle is flexed slightly with a foam wedge underneath the tibia to bring the femur parallel to the cassette.

Craniocaudal View (CrCd)

The patient is positioned in dorsal recumbency with the pelvis slightly rotated. The limb of interest is extended caudally and the opposite limb flexed, abducted and secured.

Centring and Collimation for Both Views

 Centring: Mid-femur.

 Collimation: To include hip and stifle joints and skin surfaces.

Tibia and Fibula

Mediolateral View

The patient is positioned as for lateral stifle view. A foam wedge underneath the tarsus can bring the tibia parallel to the cassette. The opposite limb is extended and secured cranially.

Caudocranial View (CdCr)

The patient is positioned as for CdCr stifle with the opposite limb flexed and abducted. On palpation the patella should be central to the femoral condyles.

Centring and Collimation for Both Views

 Centring: Mid-tibia/fibula.

 Collimation: To include the stifle, tarsus and lateral skin surface.

Metatarsus

Mediolateral View

The patient is positioned as for a lateral tarsus.

Plantarodorsal View (PlD)

The patient is positioned as for a PlD view of the tarsus.

Centring and Collimation for Both Views

 Centring: Mid-metatarsal region.

 Collimation: To include the tarsus, digits and soft tissue surface.

Flexed, Stressed and Oblique Views

When joint instability or joint fractures are suspected stressed and flexed views can be taken. The patient should be heavily sedated or anaesthetised and care taken manipulating the joint to avoid further trauma or displacement. Tape, ties and sandbags are used to maintain the joint in a flexed or stressed position as manual restraint is not allowed. Lateral oblique views may also be taken.

References

1.  Cook J, Houlton J, et al, eds. BSAVA Manual of Canine and Feline Musculoskeletal Disorders. Gloucester: British Small Animal Veterinary Association, 2006.

2.  Lavin LM. Radiography in Veterinary Technology. 4th ed. Philadelphia: WB Saunders, 2006.

3.  Thrall DE. Textbook of Veterinary Diagnostic Radiology. 4th ed. Philadelphia: WB Saunders, 2002.