Shales CJ, Langley-Hobbs SJ.
Queen's Veterinary School Hospital, Department of Veterinary Medicine, Madingley Road, Cambridge, UK. cjs24@cam.ac.uk

Vet Surg. 2005 Jul-Aug;34(4):324-31.

OBJECTIVE: To define a safe corridor in the dorsoventral plane to facilitate placement of screws inserted in lag fashion within the sacral body for fixation of sacroiliac fracture-luxation injuries in dogs.

STUDY DESIGN: Anatomic study.

SAMPLE POPULATION: Cadaveric canine sacra.

METHODS: Canine sacra (n=45) were used for a radiographic study to define a safe corridor in the dorsoventral plane for placement of screws inserted in lag fashion for fixation of sacroiliac luxation in the dog. The defined safe corridor allowed drilling to a depth of 65% of the sacral width to ensure screw purchase of > or =60%. Effects of positioning and measurement techniques were evaluated.

RESULTS: Eighty-seven safe corridors were measured. The mean articular surface was 100+/-4.52 degrees from horizontal. Mean maximum, optimum, and minimum safe corridor drill angles were 111+/- 4.57 degrees, 100+/-4.70 degrees, and 89+/-5.17 degrees, respectively, from the articular surface. Predicted surgeon error of +/-4 degrees was used to define the safe corridor for use clinically.

CONCLUSIONS: In 91% of sacra, a drill angle of 100+/-4 degrees would remain ventral to the vertebral canal. Twelve sacra (14%) were at risk of penetration of the pelvic canal. A drill angle of 97+/-4 degrees avoids penetration of the vertebral canal in all sacra measured but risks ventral exit from the body in 30% of sacra studied.

CLINICAL RELEVANCE: A drill angle of 97 degrees from the articular surface is recommended for insertion of screws for lag fixation of canine sacroiliac luxation.