Is movement asymmetry always an indication of pain?

The equine is a magnificently designed creature, with a locomotor system that is functional, energy efficient, graceful and compatible with human needs.  It is because of its unique, smooth locomotor system that horses have become partners and companions to humans, enabling us at first just to move from place to place, and later to compete in a variety of sports. Most of us recognize the inherent beauty and worth of horses as intelligent and trustworthy companions, too.

The horse’s locomotor system is not perfect, and a dysfunction in this system – or a lameness – is one of the leading reasons for veterinary consultations (Nielsen et al., 2014). Horses of all disciplines are affected by lameness, which can constitute huge losses for owners, both financially and in terms of time away from training and competing (Jeffcott et al., 1982).

Lameness refers to one or more signs of a pathological condition of the locomotor system, or an alteration in the normal gait due to a structural or functional disorder in the locomotor system (Buchner, 2013). It is up to us as therapists to use our clinical reasoning skills to evaluate each individual horse, so that we can differentiate between a normal and an abnormal gait.

When a horse presents with lameness, we face two challenges. Firstly, we need to identify whether a gait abnormality or movement asymmetry is present, and secondly, we need to decide whether or not the movement abnormality or asymmetry is an indication of pain.

Generally, we utilize our subjective gait analysis skills to identify an irregularity or asymmetry in movement, relying on our own limited visual and auditory senses. As mere humans, we’re subject to limitations in how we perceive things, due to factors such as the temporal resolution of our eyes, our perception of asymmetry and, of course, our memory (Parkes et al., 2009). Because of our limitations, there are often disagreements between observers, and inconsistencies in the documentation and recording of gait abnormalities (Hammarberg et al., 2016).

However, with recent developments in measurement systems for equine gait assessment, gait analysis is becoming more objective. We now have at our disposal kinetic systems such as pressure plates, force-measuring horseshoes and force-measuring treadmills; as well as kinematic systems such as serial photography and cine film, the use of reflective skin markers with high-speed film using 2D and 3D systems, and the simplest system of all – body-mounted accelerometers. These systems all have advantages and disadvantages; some are not at all suited for clinical use, while others are simple, portable, affordable and easy to interpret.

Research focusing on evaluating induced lameness using various objective gait analysis systems has revealed a great many indicators of lameness, some of which we can combine with subjective gait analysis, and some of which we can not. Study findings help us to better understand the effects that lameness has on the equine locomotor system, and are of great value in developing our evaluation and clinical reasoning skills. Marinette Teeling will be looking at these lameness indicators in our upcoming webinar on 6 March.

The true meaning of movement asymmetry

We need to question whether asymmetries in movement – whether measured by objective or subjective gait analysis – are always an indication of lameness or underlying pathology. It has been proven many times between 1993 (Peloso et al.) and 2016 (Sjödin et al.) that an induced unilateral lameness leads to measurable kinematic asymmetry. However, the inverse relationship has not been investigated or proven, and raises the question:  To what degree are small, measurable asymmetries in movement a direct indication of pain or underlying pathology?

Some objective gait analysis reports have suggested that up to 75% of horses in regular work test as lame when subject to rigorous lameness evaluations (Dyson & Greve, 2016). Rhodin et al. conducted two separate experiments using an objective gait analysis system; first they evaluated 201 riding horses in training, considered by their owners to be free of lameness (2015), and then they evaluated 222 horses using the same analysis system (2017). The first study revealed that 47% of the horses had movement asymmetry at a trot in a straight line, and the second study revealed 72.5% had significant movement asymmetries. Again, this raises the question: Are these movement asymmetries a sign of pain, or can we attribute them to something else?

For this, clinical reasoning and evaluation skills are essential. For each lameness we observe, we need to find ways to objectively measure gait abnormalities, and combine those observations with the rest of our evaluation, keeping as much as possible objective, measurable, recordable and repeatable. In this way we can establish for each individual horse whether or not pain and a possible pathology is at the root of the movement abnormality.

While objective data using a movement evaluation system based on tools like video and accelerometers can prove useful, such measurement tools will never replace clinical reasoning skills. To a large extent, clinical reasoning skills depend on the experience and knowledge of the observer. Even with years of experience, however, our clinical reasoning skills will remain limited if there is no conscious, ongoing effort to improve our knowledge through continuing education.

Join us in our first equine webinar on 6 March as Marinette Teeling discusses lameness and its clinical signs.  All who love and work with horses stand to benefit from a deeper  understanding of asymmetry in gait and the effects of lameness on the equine locomotor system.

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