Range of motion and between-measurement variation of spinal kinematics in sound horses at trot on the straight line and on the lunge.
Authors: Hardeman A M, Byström A, Roepstorff L, Swagemakers J H, van Weeren P R, Serra Bragança F M
Journal: PloS one
Summary
# Editorial Summary Understanding what constitutes normal spinal movement in horses is fundamental to clinical assessment, yet objective data on expected ranges of motion and their natural variability have been lacking. Hardeman and colleagues used three-dimensional motion capture to measure spinal kinematics in twelve sound horses performing twelve trotting repetitions each across different surfaces (hard and soft ground) and paths (straight lines and lunges), with measurements repeated over three separate days to capture both immediate and longer-term consistency. The researchers found that cervical lateral bending varied significantly between directions (doubling on the left lunge compared to the right), whilst mean variation for whole-back flexion-extension was notably small at 0.8°, with pelvic motion showing similarly tight parameters of 0.7–1.3°—though repeatability was somewhat inconsistent, with intraclass correlation coefficients ranging from 0.51 to 0.93 depending on the parameter measured. Critically, between-horse variation substantially exceeded within-horse variation, and spinal kinematics proved considerably more stable on soft surfaces than hard ground, with measurement repeatability declining significantly when horses were rechecked after four to eight weeks. For equine practitioners, these findings emphasise that meaningful clinical assessment of spinal function requires both individual baseline data and recognition that subjective evaluation alone cannot reliably detect minor kinematic changes—objective quantification remains technically challenging precisely because normal motion patterns are highly individualised.
Read the full abstract on PubMed
Practical Takeaways
- •Clinical assessment of spinal motion by eye alone is unreliable due to small ranges of motion (< 1 degree) and high between-horse variation; objective measurement tools should be used when quantifying spinal dysfunction
- •Each horse has an individual 'normal' baseline for spinal kinematics, making comparison to population averages less useful than tracking changes within the same horse over time
- •Surface and repetition effects matter: harder surfaces showed more variation, and motion parameters stabilized with repeated trials, suggesting consistent measurement protocols are essential for reliable clinical assessment
Key Findings
- •Range of motion in spinal flexion-extension and lateral bending varied between 0.8-1.0 degrees with mean between-measurement variation of less than 1 degree
- •Cervical lateral bending was doubled on the left compared to right lunge, indicating asymmetrical motion patterns
- •Between-horse variation was substantially higher than within-horse variation, demonstrating that spinal kinematics are highly individual
- •Intraclass correlation coefficients ranged from 0.51-0.93 depending on parameter measured, with pelvic rotations showing greater repeatability (0.76-0.93) than whole back motion (0.51-0.91)