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TPLO

Course

2008

Sept 12-13th

TPLO course

now accepting

registration.

Method for Adjusting Positioning for the DAR Radiograph

By Theresa Devine Slocum, MS and Barclay Slocum, DVM

    The basic position for the DAR radiograph is sternal recumbency of the patient with the hips flexed, and the hocks adjacent to the thorax and raised 2-3 inches above the level of the radiographic table.  Palpation indicates the tuber sacrale is directly above the tuber ischii and that the radiographic beam would pass vertically through this axis.  The dorsal spinous processes can be palpated in the sagittal plane to prevent torsion of the pelvis.  The radiograph is taken using an eight by ten cassette with the patient in this position.  In normal patients, correct alignment is easily attained on the first radiograph.  The dorsal acetabular rim will appear 3mm ventral to the tuber ischii in a correctly positioned DAR radiographic view.  If the patient has pathologic changes, however, positioning is often more difficult.  This paper presents a method to determine the necessary adjustment for correct alignment based on the first DAR taken, and the lateral radiograph.

    Correction of the amount of pelvic rotation around a medial to lateral axis will bring the DAR to 3mm beneath the tuber ischii.  This can be done best by rotating the radiographic head around an axis parallel to the medial-lateral axis of the pelvis.  The amount of rotation can be calculated from both the first DAR and lateral view.

1. On the DAR radiograph, measure the obtained distance from the tuber ischii and the dorsal acetabular rim.

2. On the lateral radiograph, draw a line that is tangent to the tuber ischii and whose perpendicular distance from the acetabulum is the same as the distance obtained in step 1.

3. On the lateral radiograph, draw a line that is tangent to the tuber ischii and whose perpendicular distance from the acetabulum is 3mm.

4. Measure the angle formed by the intersection of the two lines obtained in step 2 and 3.

5. Rotate the radiographic head that angle, and align the cassette to the beam.

This method will attain the ideal position for the DAR on the first attempt.

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