Cyclogram analysis of canine gait: quantifying inter-joint coordination and clinical utility in rehabilitation.

Introduction: Cyclograms, or joint angle-angle plots, provide an intuitive representation of inter-joint coordination, yet they remain underused in canine rehabilitation. This study established sagittal-plane hindlimb cyclograms in dogs and evaluated the absolute enclosed cyclogram area (A_abs, deg²) as a reproducible and clinically interpretable index of coordination. Methods: Eight clinically healthy Beagles were recorded during treadmill walking, and hip-stifle and tarsus-stifle cyclograms were generated from 10 consecutive gait cycles per dog. A_abs was calculated using a polygonization-based approach applied to the cyclogram trajectory. Within-session repeatability was assessed using ICC(1,1) and ICC(1,10), together with measurement-error indices (SEM and MDC95). Clinical feasibility was illustrated in a client-owned dog undergoing rehabilitation after unilateral femoral head and neck ostectomy (FHNO), assessed during overground walking on postoperative days (PODs) 14, 21, and 31, with 10 gait cycles analyzed per session. Results: In healthy Beagles, the hip-stifle cyclogram formed a broad counterclockwise loop, whereas the tarsus-stifle cyclogram exhibited a characteristic figure-of-eight pattern. Mean A_abs was 813.18 ± 114.88 deg² for hip-stifle and 619.88 ± 129.00 deg² for tarsus-stifle. Stride-level repeatability was moderate [ICC(1,1) = 0.59 and 0.67], whereas the mean of 10 cycles showed excellent repeatability [ICC(1,10) = 0.93 and 0.95], with small MDC95 values for the 10-cycle mean (81.55 and 78.23 deg²). In the FHNO dog, cyclogram loops were initially tall and narrow on POD14, reflecting stifle-dominant motion with restricted hip and tarsal excursions, and became progressively wider and smoother by POD31. Consistently, mean A_abs increased from POD14 to POD31 (hip-stifle, 112.24 to 395.09 deg²; tarsus-stifle, 185.73 to 543.78 deg²), whereas stride-to-stride variability decreased (coefficient of variation, 66.76% to 30.61% and 77.32% to 42.18%). Discussion: These findings indicate that hindlimb cyclograms provide a compact visual summary of inter-joint coordination and that A_abs offers a reproducible quantitative descriptor in healthy dogs. In a single FHNO case, this metric also illustrated feasibility for tracking early postoperative gait changes in a clinical rehabilitation setting.