Proximal hindlimb flexion in the horse: effect on movement symmetry and implications for defining soundness.

This research investigates the impact of applying a specific technique, proximal hindlimb flexion, on the symmetry of horse movement. The study found that this flexion can exacerbate subtle asymmetry in horse movement and may potentially aid in detecting minor lameness in horses.

Objective and Methodology

• The main objective of this study was to understand the effect of proximal hindlimb flexion on horses’ movement symmetry. This technique is commonly used in pre-purchase evaluations and clinical lameness examinations, yet very few studies have quantified its impact.
• 13 horses with symmetric movement were selected for this study. The researchers attached inertial sensors to these horses’ left and right tuber coxae and os sacrum to measure vertical movement symmetry at trot before and after the flexion testing. This process was repeated after 5 minutes.
• Researchers recorded videos of all the horses and analyzed the recorded movements visually.

Research Findings

• Upon conducting proximal hindlimb flexion tests, the researchers observed changes in movement symmetry. The effects were smaller when stride number increased.
• The most significant impact was observed as a decrease in the upward movement of the os sacrum following mid-stance of the flexed limb and an increase in upward movement of the non-flexed limb. This manifested as a ‘hip hike’ of the flexed limb, indicating increased movement asymmetry post flexion.
• The study also found that the flexibility test can potentially enhance movement symmetry based on individual baseline asymmetry.

Conclusions and Future Directions

• Proximal hindlimb flexion, performed carefully, can amplify subtle asymmetry, providing insights into a suspected lameness in horses.
• The technique generated variable responses within and between horses, leading to the conclusion that individual responses to flexion were variable.
• The researchers suggested that proximal hindlimb flexion could elevate the asymmetry of a slightly lame horse above the threshold, which could aid in clinical gait examinations.
• The study concluded with a call for further research to understand why horses respond positively to flexion and the possible differences in response among sound and lame horses across different athletic disciplines.