Equine Lameness Assessment: Biomechanics, Locomotion, Forces and Central Pattern Generators

by | Mar 3, 2022 | Equine Therapy

Like many of you, I have studied many of Hilary Clayton’s books and research articles over the years, both as a student and a Vetrehabber. It was an incredible privilege for me to hear her lecture  on our Onlinepethealth platform over the last two months.

Dr Clayton presented four lectures on the biomechanics and locomotion of the horse, covering conformation, structure, ground reaction forces, hooves, concussion, central pattern generators, movement adaptations to lameness, lameness assessment techniques, and so much more.

Below, I share my highlights from these four incredibly insightful and evidence-based lectures.

 

More than four hours of CPD

Dr Hilary Clayton presented four lectures to the Onlinepethealth Equine members, on:

  1. Structure and Function of the Equine Locomotor System
  2. The Relationship Between Forces and Movement
  3. Locomotor Control and its Effect on Performance
  4. How the Horse Adapts to Lameness

Each lecture focuses on a different aspect of biomechanics, gives evidence-based information with multiple references to publications, and highlights Dr Clayton’s experience, insight and vast knowledge.

These lectures are all available to watch on the Onlinepethealth Equine members portal. I highly recommend that every Onlinepethealth equine member takes the time to watch them!

 

Structure and function of the Equine Locomotor System

Conformation

While anatomy may be roughly the same for all horses, their individual conformation differs widely. A great deal of variation occurs among horses, and these differences will directly impact an individual horses’ performance and soundness.

Dr Hilary starts off this series by discussing conformation; how it is determined and how we can evaluate it. The skeletal structure of the horse – the length of bones, together with the angles between the bones – will determine the weight the limbs can support and the propulsion they can generate.

The relationship between available weight-bearing capacity and propulsion is inverse – the more the horse’s weight-carrying capacity, the straighter the limbs and the less propulsion available. The opposite is also true. The forelimbs of the horse are straighter, allowing weight carrying capacity, while the hindlimbs have more angulation, highlighting their function of providing propulsion to the body.

The muscular structure of the horse will act to move and stabilise the skeletal structure, and can fulfil different functions depending on their individual fibre type, length, direction and activation. Primary movers will have long, parallel muscle fibres which can rapidly contract through a large range of movement. Stabilising muscles will have fibres arranged at an angle to the long axis of the muscle, making the available range of motion much smaller.

Muscle contraction

Understanding when and how a muscle contracts concentrically, eccentrically and isometrically can significantly help us to tailor rehabilitation exercises towards a specific goal. As the primary extensor of the elbow, the triceps contracts concentrically in late swing phase to extend the elbow in preparation for ground contact. Through the stance phase, the triceps remains eccentrically activated to prevent flexion of the elbow.

Ground contact

How the horse contacts the ground with the hoof is an important consideration for its long-term soundness. Understanding the implications of a healthy heel-first contact and how concussion is absorbed through the hoof is essential to understanding how we can maintain the health and wellbeing of the distal limbs of the joints.

Dr Hilary goes into great detail about these mechanisms of action. To learn more about ground contact, concussion forces and dispersion of force through the hoof, watch this webinar in the Onlinepethealth Equine members portal.

 The Relationship Between Forces and Movement

Ground reaction forces

In this lecture, Dr Hilary takes a deep dive into ground reaction forces and how they affect posture, balance and movement in horses. Understanding the vertical, longitudinal and transverse components of GRFs allows us to evaluate the force placed on the horse’s limbs and body during specific movements, disciplines and activities, and the impact on the long-term soundness and performance of the horse.

Thoughts to ponder

At the end of this 1.2-hour lecture, Dr Hilary leaves us with the following conclusions or thoughts:

  • Both show jumpers and dressage horses are required to work with greater angulation of their hindlimbs, requiring a great deal of soft tissue strength and support.
  • The supporting soft tissue must be conditioned gradually over a period of time.
  • Strength must develop together with the technical skill and ability of the horse.
  • It is the development of strength that defines the progress of the horse from lower levels of competition or performance to higher levels.

To find out how exactly these conclusions are based on GRFs, watch Dr Hilary Clayton’s lecture in the Onlinepethealth Equine Members portal.

 

Locomotor Control and its Effect on Performance

This lecture was all about central pattern generators (CPFs) – the nervous system, how it regulates and controls movement and rhythm, and how we can and cannot influence it. This was by far my favourite of the four lectures, diving into the different gaits, various abnormalities in movement that can be attributed to CPGs, and the ways in which we can retrain or teach new motor skills outside of the normal gait repertoire.

In a few weeks’ time, Amie Hesbach and Gillian Tabor will be joining us for a live four-part webinar series focusing on neurodynamics in the equine patient.

When it comes to truly understanding the nervous system and how we can affect it from a training and rehabilitation point of view in every patient, this webinar series is key. It will help us reform our foundational understanding, bring new ideas and open up discussion among us.  Do try to watch it!

 

How the horse adapts to lameness

Man vs Machine

Equine lameness evaluation is an area that we have developed, studied and attempted, over many years, to make more objective. The greatest challenge we as clinicians face is that we rarely agree on the degree of unsoundness seen, or the limbs affected, especially in the case of mild lameness.

The development of objective lameness assessment tools such as force plates and inertial sensors has helped us to become more objective and better able to see very small changes in symmetry in the stride, as well as to identify the affected limbs more easily.

Dr Hilary discusses the merits and disadvantages of both man and machine, and concludes that the greatest advantage can be drawn when we combine observations of the whole horse with the data collected from lameness assessment tools.

You can take a deep dive into the research and the reasoning behind this conclusion in the webinar with Dr Hilary Clayton.

Adaptations to lameness

Forces never disappear; they are just redistributed to other limbs.

Focusing on the trot, Dr Hilary Clayton explains the adaptations occurring in the gait as a result of low-level lameness that can be difficult to identify. Some of the adaptations in low-level lameness that she discusses include:

  • how slowing the speed of the trot reduces the peak vertical force;
  • how a decrease in suspension phase and a flattening of the trot will reduce peak vertical force; and
  • how the duration of the stance phase can be increased to reduce peak vertical force.

As the degree of lameness increases, the adaptations change, too. The horse may adapt the gait by

  • shifting weight to the other limb in the diagonal pair, resulting in a head nod;
  • shifting the vertical force from the lame diagonal onto the compensating diagonal.

We will be able to observe some changes in movement with our eye, including a head nod, a shortening of the limb protraction phase, the amount of extension of the fetlock joints, and the movement of the sacrum at the midline of the pelvis. Others are more difficult to discern by observing the horse directly.

One of the ways we can improve our lameness evaluation abilities, according to Dr Hilary Clayton, is by carefully studying a computer-aided learning programme of the horse’s various gaits, which will hone our observation skills and equip us to spot aberrations. She recommends this free resource to anyone who would like to develop skills in this area: www.lamenesstrainer.com

 

Conclusion

The better we understand biomechanics, locomotion and the adaptations the horse uses when experiencing lameness, the better we can evaluate, treat and help our patients on a daily basis. If you’re an Onlinepethealth Equine member, this series of lectures by Dr Hilary Clayton should be prioritised on your ‘what to watch’ list!

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