A morphometric study of the canine skull and periorbita and its implications for regional ocular anesthesia.

OBJECTIVE: A hypothetical relationship between canine cranial length and the length of the periorbita could be used for intraconal anesthetic volume estimation.

STUDY SUBJECTS: Forty-one canine cadaver heads and one macerated dog skull.

PROCEDURES: Inion and nasion points were recognized in the macerated skull and used as landmarks for cranial length measure. Thirty cadavers classified as dolichocephalic, mesaticephalic and brachycephalic were distributed in three study groups. Anatomic references of the skull shapes were recognized and parameters measured: body weight (BW), cranial length (Lcr ) and length of the periorbita (Lpo ). Results were compared and statistical analyses were performed to find correlations between BW and the skull parameters. Contrast medium was injected in another 11 cadavers with a total volume calculated based on Lcr (10 cadavers) or BW (one cadaver) and then submitted to computerized tomography examination to compare techniques, estimate the capacity of the intraconal space of the periorbita and to illustrate practical implications.

RESULTS: There is a positive correlation between BW and Lpo (P < 0.001) as well as between Lcr and Lpo (P < 0.0001). Linear regression of the variable BW predicts only 71% of the variable Lpo (r2 = 0.71), whereas the variable Lcr predicts 88% (r2 = 0.88) of Lpo .

CONCLUSIONS: This study demonstrated a mathematical relation between Lcr and Lpo . A method for calculating anesthetic solution volumes based on canine morphometric features is presented. The formula 0.1 mL/cm Lcr to calculate total intraconal anesthetic volume is suggested.