In this fascinating article Founding Vet-IR Member & Equine Documentalist Yogi Sharp, talks about IR technology and how it can help to objectively establish regions of pain associated with more subtle asymmetries…
The recognition of subtle lameness or subclinical pain has proven to be elusive to the general horse owner population. Popescu et al (2016) found that owners missed veterinary recognised diagnosis in 82% of cases presenting with grade <3 lameness. This finding echoed the discussions of Keegan (2007) which stated that the observers experience played a large role in their ability to define lameness and therefore there was a low observer agreement. Even amongst vets, observer agreement is questionable, Dyson (2013) discussed clinical observation explaining how it is often subjective and highlighted the need for the horse to be “lame enough” for recognition of improvement after the administration of diagnostic analgesia.
Dyson has also published studies outlining the lack of recognition of more subtle lameness, Dyson et al (2019) took a random convenience selection of 20 horses, that were in regular work and found 16 of them to be lame, that’s 80% that were working with lack of a recognition of their lameness.
The question is how can we recognise pain in the horse before we get to the point at which they are lame enough, especially when the recognition of subtle lameness is so low. Dyson et al. (2019) built on a previous study (Mullard et al 2017) which created an ethogram to assess the facial expressions and behaviours in a first step toward easier recognition of lame horses, giving professionals a way of recognising pain over and above obvious gait or postural changes. Dyson et al. (2020) found that “the ethogram was applied consistently by veterinarians with differentiation between nonlame and most lame horses. After appropriate training in its application, the ethogram may provide a useful tool for determining the presence of musculoskeletal pain in horses performing poorly”.
The ethogram discovered 24 behavioural markers, the presence of 8 or more indicted musculoskeletal pain. It is becoming more recognised that drops in performance can also be attributed to musculoskeletal dysfunction (Dyson 2015), however as stated studies show that the ability of riders and trainers to recognise this is poor and often the problem is put down to rider error, behaviour or even deemed normal for that horse. Owners, trainers and every type of practitioner has got to come to the realisation that horses are trying to tell us something.
In that regard, Popescu et al. (2016) highlighted the need for educating the owner in the recognition of subtle lameness to enable earlier detection and therefore treatment, the ethogram could prove to be a valuable tool in that education and should be studied by any and every horse owner.
Something Dyson (2013) stated was that clinical observation can be a great tool in identifying lame limbs but mostly the assessment is non-specific and requires further diagnostic tools, this logically becomes even more indiscriminate in more subtle lameness.
Posture is emerging as a more widely recognised indication of pain or dysfunction, however there is limited peer reviewed research on the subject. Seneque et al. (2019) discussed how back pain, something widespread and again hugely missed can create postural adaptation. The study also stated Stress, fear, discomfort or pain produce contractions of the back muscles, affecting posture and impairing the biomechanics of the dorsal body outline (i.e. back and neck) and result in deterioration of the musculoskeletal structures. It used morphometric measurements to quantify posture of the back, neck and head as welfare indicators but not necessarily indications of pain or lameness.
The studies of Gellman and Shoemaker have explored posture and outlined seemingly abstract influences on it. They highlight the importance of neutral posture, being 4 legs square and emphasis camped under as a compensatory posture, any other posture than one with vertical metacarpals/tarsals is a compensatory stance, an abnormal posture resulting from external or internal alterations to the reflexive postural control mechanisms. They state the most common causes of compensatory stance are: structural damage (scars) to the musculoskeletal system, altered nerve signal transmission due to inflammation along the nerves or spinal cord, receptor damage or down regulation (number of receptors is decreased), or distortion of the normal structures of regions rich in postural signals, such as the upper cervical muscles, feet or temporo-mandibular and dento-aveolar joints. In the authors experience camped under posture behind is commonly found with negative plantar angles and the pathologies found linked to this hoof conformation.
Articles on these connections can be found following this link.
So now the question is, how do we quantify subtle, sub clinical, non-specific lameness or pain once we have recognised it in our horse?
Firstly, there must be an emphasis on monitoring and early detection technologies if we are to have any hope of ending the reactive mindset of our current management protocols in favour of more pro-active and preventative practices.
Keegan (2007) discussed objective gait analysis as a useful tool in quantifying observations of lameness and the technology is emerging as an integral part of monitoring performance. Braganca et al. (2018) reviewed the use of objective gait technologies, it expressed how more and more subtle gait asymmetries are now measurable, and that this technology would prove to be useful in the longitudinal monitoring of sound and lame horses. However, gait asymmetry does not necessarily constitute pathology or pain as natural laterality comes into play, this new ability to measure signals of lameness otherwise invisible to the naked eye raises new questions as to the definition of lameness. Perhaps what the defining factor is, is the presence of pain. For the most part, currently, this decision remains down to the experience of the vet, but that still retains a certain amount of subjectivity. For more profound lameness, diagnostic analgesia would aid in correlating this asymmetry with pain, however as stated previously, this becomes infinitely more indiscriminate as the lameness becomes more subtle.
So how can we objectively establish regions of pain associated with more subtle asymmetries?
Thermography (IR), due to its advancements in equipment, image acquisition protocols and veterinary interpretation, is becoming an informative complimentary diagnostic modality (Soroko and Howell 2018). Studies have shown it to be a useful tool in detecting areas of pain (Vainionpaa et al 2012), although this study was in cats there are now many studies discussing its efficacy in equine diagnostics. Talas and Talas (2020) explained that it can be used efficiently as an inexpensive and rapid pre-diagnostics tool to localise or establish a strong suspicion of certain abnormalities before directing the patient towards further imaging diagnostics. While thermography does not show structure, meaning its most beneficial used in conjunction with other modalities, it enables the practitioner to see areas of inflammation and physiological dysfunction. It has proven effective in the diagnosis of soft tissue pathology and superficial bony lesions, it also has a unique advantage in the detection of early pathology as physiological changes often occur before clinical signs (Eddy et al 2001, Redaelli et al 2014).
Of course thermography, as with any modality, has its limitations, the method is only capable of recording surface body temperature. Extensive experience has shown that measurements of deeper-lying (>5-6 cm) tissues are limited and further confounded by the lack of information about the exact depth of the heat source. Therefore, thermography is best used for the analysis of structures found close to the surface, such as muscles, joints, ligaments, tendons, teeth, and soft tissues (Talas and Talas, 2020), however as further research into pattern recognition is undertaken we may see deeper and deeper pathologies understood thermographically. The reliability of thermography is also subject to both the protocols followed in acquisition and the subsequent interpretation, if the images are not acquired in a controlled environment after appropriate preparation, they can produce artefacts. Experience is vital in correct interpretation as current veterinary training does not cover recognition of thermal pattern variations (Soroko and Howell 2018).
Having stated some of its limitations and where these are understood, thermography has been shown to be effectively utilised in the prevention, detection and monitoring of equine musculoskeletal pathology (Talas and Talas 2020, Soroko and Howell 2018, Turner 2001), it was shown to have an excellent correlation between trainer-perceived problems and veterinarian diagnoses, but importantly detect pathology before the presentation of clinical signs (Turner 2001). Soroko and Howell (2018) expressed how periodic routine thermographic evaluation of working sport and racehorses could assist in the design of training programs and aid injury prevention.
In relevance to this article and to conclude, the unique ability for thermography, when used and interpreted correctly, to detect the bodies response to dysfunction, at a far earlier stage then any other modality means it can be a vital tool in quantifying the subclinical pain and lameness we can detect by applying the ethogram and/or objective gait analysis. The fact is that we, both owners and professionals, are failing to recognise pain and lameness in our horses, but there is technology available now that we can use regularly to “check up” on our horses physiological state. Perhaps as we enter a new era of preventative and holistic care we should consider these technologies and findings that enable pro-action and give us the ability to quantify the subclinical.
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Dyson, 2015, Evaluation of poor performance in competition horses: A musculoskeletal perspective. Part 1: Clinical assessment, https://doi.org/10.1111/eve.12426
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F.M.Serra Bragança, aM.Rhodinb, P.R.van Weerena, On the brink of daily clinical application of objective gait analysis: What evidence do we have so far from studies using an induced lameness model? The Veterinary Journal, vol 234, 2018, pg 11-23