CT-based optimization of hindlimb muscle measurement levels and development of a hindlimb muscle condition score in dogs.

INTRODUCTION: Objective assessment of hindlimb skeletal muscles in dogs remains challenging in small animal practice. This study aimed to use computed tomography (CT) to characterize hindlimb muscle distribution, identify optimal measurement levels, and evaluate the clinical applicability of a palpation-based hindlimb muscle condition score (hMCS) system. METHODS: This prospective observational study included 39 dogs (76 hindlimbs) enrolled according to the predefined inclusion criteria. CT was used to measure the muscle cross-sectional area (CSA) and calculate the muscle ratio (muscle CSA/total CSA) at the three femoral levels. For the tibia, the location of the maximal gastrocnemius muscle CSA was identified, and measurements were performed at that level. Associations with clinical variables [weight, age, sex, body condition score (BCS), hMCS] were analyzed, and the interobserver reliability of the hMCS was evaluated. RESULTS: Muscle CSA and muscle ratio differed significantly among the femoral levels, with the highest values at the mid-femoral level. In the tibia, the maximal CSA of the gastrocnemius muscle was consistently located in the proximal region. Body weight was positively associated with muscle CSA across all levels, whereas age and BCS were negatively associated with the muscle ratio at most levels. The hMCS showed excellent interobserver reliability and significant associations with CT-derived muscle measurements. DISCUSSION: The mid-femoral level appears to be a representative site for evaluating femoral muscle mass in dogs, whereas the proximal tibial level provides a practical approach for assessing the crus musculature. Muscle CSA primarily reflects body size, whereas muscle ratio more sensitively reflects compositional changes. The hMCS may serve as a practical complementary tool for hindlimb muscle assessment in dogs.