Sacroiliac Luxation in the Cat: Defining a Safe Corridor in the Dorsoventral Plane for Screw Insertion in Lag Fashion

Objective—To define a safe corridor in the dorsoventral plane within the feline sacral body for placement of screws inserted in lag fashion for repair of sacroiliac luxation.
Study Design—Anatomic study.
Sample Population—Frozen cadaveric feline sacra.
Methods—Feline sacra (n=20) were used to perform a radiographic study to define a safe corridor to a depth of 66% of the sacral body width. Two drill start points (A and B) were evaluated. Dorsal exit from the safe corridor was considered unacceptable.
Results—Forty safe corridors were measured. The mean articular surface was 100±6.4° from horizontal. Mean maximum, optimum, and minimum safe corridor drill angles from drill point A were 107±6.8°, 97±6.9°, and 87±7.2°, respectively, from the articular surface. Mean maximum, optimum, and minimum angles from drill point B were 109±7.2°, 99±7.1°, and 89.5±7.2°, respectively. Point B increased the risk of ventral exit from the sacral body.
Conclusions—Point A and a drill angle of 90±4° for drilling of the feline sacral body is recommended. This margin for error risks ventral exit from the body in 23/40 (58%) of the sacra in this study. Reduction of the margin for error to ±2° would reduce the risk of ventral exit to 14/40 (35%) of the sacra in this study.
Clinical Relevance—Drilling at 90° to the feline sacral articular surface is recommended. Findings from this study present a strong case for use of angled drill guides.