CT scan based determination of optimal bone corridor for atlantoaxial ventral screw fixation in miniature breed dogs


Corresponding Author

Franck Forterre, DVM, Dr. med. Vet, Diplomate ECVS, Small Animal Clinic, Neurosurgery, Vetsuisse Faculty of Berne, Länggassstrasse 128, 3012 Berne, Switzerland. E-mail: franck.forterre@vetsuisse.unibe.ch



To describe the most reliable insertion angle, corridor length and width to place a ventral transarticular atlantoaxial screw in miniature breed dogs.

Study Design

Retrospective CT imaging study.

Sample Population

Cervical CT scans of toy breed dogs (n = 21).


Dogs were divided into 2 groups—group 1: no atlantoaxial abnormalities; group 2: atlantoaxial instability. Insertion angle in medial to lateral and ventral to dorsal direction was measured in group 1. Corridor length and width were measured in groups 1 and 2. Corridor width was measured at 3 points of the corridor. Each variable was measured 3 times and the mean used for statistical analysis.


Mean ± SD optimal transarticular atlantoaxial insertion angle was determined to be 40 ± 1° in medial to lateral direction from the midline and 20 ± 1° in ventral to dorsal direction from the floor of the neural canal of C2. Mean corridor length was 7 mm (range, 4.5–8.0 mm). Significant correlation was found between corridor length, body weight, and age. Mean bone corridor width ranged from 3 to 5 mm. Statistically significant differences were found between individuals, gender and measured side.


Optimal placement of a transarticular screw for atlantoaxial joint stabilization is very demanding because the screw path corridor is very narrow.