Inertial measurement units are comparable to motion capture for measuring intersegmental spinal angular velocities in horses

Objective: To compare inertial measurement unit (IMU)-derived intersegmental spinal motion data with measurements obtained from a marker-based motion-capture system. Methods: 4 horses were instrumented with custom marker clusters incorporating a 3-D-printed base designed to secure the IMU, ensuring both systems recorded data from the same anatomical location and orientation. A total of 3,737 paired time points across 37 gait cycles were analyzed. Agreement in intersegmental angular velocities across 3 planes of motion was evaluated using Bland-Altman analysis and intraclass correlation coefficients. Results: Bland-Altman analysis demonstrated no significant systematic bias between methods. Intraclass correlation coefficients indicated excellent agreement in 7 of 9 comparisons (r = 0.964 to 0.991) and good agreement in the remaining 2 comparisons (r = 0.854 and 0.875). Conclusions: IMUs provide a valid alternative to marker-based motion-capture systems for measuring intersegmental angular velocities in horses. Clinical Relevance: Strong agreement between IMU and motion-capture data supports the use of IMUs for assessing topline function in nonlaboratory, clinically relevant settings.