Comparison of two postoperative complication grading systems following an elective orthopedic procedure in dogs.

INTRODUCTION: A standardized system for grading postoperative complications in veterinary orthopedics was proposed in 2010 by Cook et al. categorizing complications as minor, major, or catastrophic. Despite broad acceptance, complication rates still vary widely between studies. An alternative to the Cook system has been proposed; the adapted Clavien-Dindo (aCD) system, which categorizes five complication grades and distinguishes them from two other outcomes: 'sequelae' and 'failures-to-cure'. The objective of this study was to compare postoperative complication rates in dogs undergoing tibial plateau leveling osteotomies (TPLO) using both systems. We hypothesized that there would be no significant difference in complication rates between grading systems. METHODS: Dogs undergoing TPLO between December 2023 and January 2025 were prospectively enrolled. Owner consent was obtained to review medical records and perform serial surveys for potential postoperative complications. A single investigator graded events with the Cook and aCD systems. Complication rates were compared with McNemar's χ2 test (α < 0.05). RESULTS: Eighty-five TPLO procedures in 79 dogs were evaluated. Using the aCD system, the complication rate was 28.2% while the Cook system reported 54.1%. McNemar's χ2 test showed a significant difference (p < 0.001) between systems. Twenty-six percent of Cook-classified complications were considered non-complications by the aCD system. DISCUSSION: We rejected our hypothesis that the Cook and aCD grading systems would yield comparable postoperative complication rates. The Cook system classified approximately twice the number of events as complications compared to the aCD system. A grading system with greater categorical resolution that distinguishes true complications from expected outcomes may provide a more clinically relevant assessment of postoperative risk.