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Brief Review of common Diagnostics

Introduction

Lameness diagnosis is not a straightforward process, it requires both skill and experience, firstly recognising the lame limb, identifying through palpation any abnormalities, locating the potential cause of pain and then utilising the appropriate diagnostic tools, understanding their advantages and limitations. Just this process, putting aside the actual application of the diagnostics is a learned skill that is enhanced through practice and guidance. (Dyson 2013)

This paper will appraise the different diagnostic techniques for lameness assessment, their applications, advantages, limitations and health and safety implications.

Clinical observation

Clinical observation is the first port of call in diagnostic assessment, observing a horse at rest and dynamically, with the use of flexion tests and palpation, can be the first step in locating potential causes of pain, however, as discussed by Dyson (2013) this process can be subjective, sometimes the lameness can be too subtle for the eye. Correct surface selection and utilising both straight line and circle lunging are needed to correctly identify different types of lameness, clinical observation can be a great tool in identifying lame limbs but mostly the assessment is non-specific and requires further diagnostic tools, bilateral lameness is also difficult to detect, however diagnostic analgesia can be utilised to help achieve an accurate diagnosis (Dyson 2013)

Perhaps a better way of assessing lameness as discussed by Keegan (2007) is the use of kinetics and Kinematics to more subjectively quantify lameness.

Diagnostic Analgesia

Nerve blocks must be performed systematically and accurately to be a reliable diagnostic tool, it is widely discussed that diffusion of anaesthetic can result in unintended abolishment of pain (Dyson 2013, Schumacher et al 2013). Dyson (2013) discussed in depth the complexed possible false negatives bought about by this limitation of the modality, it stated that methods are not entirely specific or reliable, however this should not detract from the importance of diagnostic analgesia. Schumacher et al (2013) outlined the false results from diagnostic analgesia, it mentioned that subtle mistakes in administration can lead to incorrect structures being blocked. The importance of the horse being “lame enough” to detect changes in lameness severity and the importance of reassessment being made before diffusion of anaesthetic, are important factors and potential limitations in ensuring diagnostic analgesia is a useful tool (Dyson 2013, Schumacher et al 2013). Both Dyson (2013) and Schumacher et al (2013) established that correctly administered diagnostic analgesia is an essential tool in locating lower limb lameness (Fig.1).

Diagnostic Analgesia health and safety

The direct health and safety implication of diagnostic analgesia is potential for infection from penetration. Schumacher (2009) outlined that if the injection is administered subcutaneously, infection is unlikely, a non-sterile penetration of synovial structures could result in disastrous effects, Schumacher (2009) also explained that sedation can be administered to ensure safety to both the handlers and a fractious horse as long as it doesn’t inadvertently interfere with the severity of the lameness.

Radiography/X-rays

X-rays are only as good as the person taking the images, x-rays can suffer from lack of definition making them difficult to read (Fig.2), human error can lead to artefacts, over exposure, under exposure and scatter, all of which can result in a subclinical x-ray (Thrall 2013). Thrall (2013) outlined that digital x-ray Pre-processing and processing steps help to create more accurate images for interpretation, however, the user still has a responsibility to follow a protocol to ensure a useful x-ray. Also discussed was the quality of hardware at the interpreters disposal; monitor quality and the lighting of the room, can play a role in the accuracy of the interpretation. Digital x-rays provide a much more reliable and cost effective modality than analogue, however there are still potential cons and limitations outlined by Thrall (2013), one being the fact that the software makes allowances for human error, where overexposure can be easily recognised in analogue the corrections made by the digital programme can mean patients and personnel receiving higher doses of radiation without recognition, however, if correct health and safety protocols are being adhered to this would be picked up.

Drost et al (2008) and Jimenez et al (2008) discussed in detail the many artefacts that can cause misdiagnosis of x-rays, they stated that even though technological advances enable x-rays to be configurated digitally without the need for further patient exposure, there is still the importance of the original image being free of technical errors to ensure correct diagnosis, an example being if the original badly exposed image is enhanced, although the image is now readable, subtle radiographic findings may still be clouded by the initial technical error. Jimenez et al (2008) set out the potential artefacts in the following series of tables (1-5) showing how they can be created and remedied at every stage of the process.

X-ray health and safety

The main consideration for x-ray safety is to limit the exposure to radiation for all parties involved in the process, potentially harmful levels of radiation are more likely to affect professionals involved in the x-ray taking process then the actual patient, unless the patient is undergoing frequent exposures. Exposure below a certain level is unlikely to produce adverse effects, however x-rays should only be utilised if the benefits outweigh the risks of radiation exposure. There should be strict protocols in place, in practice to ensure exposure remains below the safe level. (Thrall 2013)

Utlrasonography

Due to it being cost effective and portable, ultrasonography has become the most commonly used modality for soft tissue evaluation (Fig.3) (Alzola et al 2017). Alzola et al (2017) expressed that although scoring systems for evaluating soft tissue injuries are evolving, at present there is not a universal system. The subjectivity of image analysis creating differentials in reliability and repeatability is the main limitation of the modality, (Pickersgill et al 2001, Alzola et al 2017) While practitioners agreed on the echogenicity of images being either hypoechoic or anechoic the severity was subjective, Pickersgill et al (2001) concluded that due to the variability of image reading, comparison of the same case by different observers could result in inaccurate interpretation results, the same observer should ideally analyse all images taken in a certain investigation and subsequent investigations, a limitation if the animal moves to a new vet.

Ultrasonography health and safety

Apart from the potential to require sedation for fractious horses (Genovese et al 1986) there is little documentation on the potential risks of ultrasonography to the equine, however there are potential bioeffects associated with its thermal mechanisms (Miller 1991).

Magnetic resonance imaging (MRI)

MRI enables a high tissue contrast image, this makes it an increasingly favoured modality for assessing articular cartilage, ligaments, tendons, joint capsules, synovium and bone marrow, MRI provides both structural and physiological data, it can be presented as a 2D “slice” of the subject enabling the viewer to see intended structures without the possible superimposition of superficial structures (Fig.4) (Murray 2011).

Artefacts in MRI are no less potential than in other modalities, Smith (2010) outlined the various causes of MRI artefacts (Table 6), off-resonance, system limitations and subject motion being the most prevalent, Smith (2010) stated that proper scanning technique can eliminate the majority of artefacts, however due to the complexity of the modality there can still be a variety of artefacts that may need correcting, MRI technologies do provide techniques to minimize inevitable artefacts post screening but recognition of these artefacts is utmost in ensuring correct interpretation. The necessity for complete immobility can be a limitation in MRI acquisition, although the horse can be sedated, even natural sway and bodily functions can interfere with the accuracy of the images (Murray 2011).

MRI health and safety

The main consideration for MRI safety is the strong magnetic field that could potentially make any magnetic objects into projectiles, radiographs are often taken to ensure no presence of metal objects, horse shoes should be removed ensuring no nail remains in the hoof. MRI’s can be noisy and scary for horses, so considerations should be made to ensure the horse is relaxed (Murray 2011).

Venograms

Venograms are a radiographic technique using radiopaque dye to visualise and assess the vascular structures of the foot and associated lameness, they give the observer an indication of pressure, loading and degeneration (Fig.5) (Rucker 2010). This modality enables vascular tissue evaluation of the foot as pathology causes loss of integrity, this can not be easily recognised through other traditional screening modalities making venography a unique tool in the diagnosis and treatment of laminitis, with regular venograms, treatment can be assessed and altered over short periods rather than waiting between shoeing cycles to determine direction of pathology (Rucker 2010).

Abnormal venograms can be caused by technical error (fig.6), incorrect amounts of contrast material can mean blood vessels fail to be filled, this can be a limitation of the modality, causing non-filled vessels to be misdiagnosed as poor perfusion, diffusion of contrast material can also cause a “cloudy” image and pools of material on the x-ray, if the horse is stood on the foot to be imaged too long before the x-ray is taken this can cause a lack of contrast in the image (D’Arpe 2010).

Venogram health and safety

As the contrast material is administered with a needle the same sterilisation process as diagnostic analgesia should be adhered to, to avoid infection. D’Arpe et al (2010) outlined the process of administration, including sedation of the horse to ensure it is safe and clean.

Thermography

Thermography is the least invasive screening modality (Redaelli et al 2014) that has increased in its reliability and repeatability with the introduction of improved cameras, image processing and the application of strict screening protocols (Eddy et al 2001). 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 (fig.7), it has proven effective in the diagnosis of soft tissue pathology (fig.8) 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). The reliability of thermography is 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 (Fig.9) (Soroko and Howell 2018).

As more research is done into the modality, there will be deeper understanding of its potential applications and wider user confidence, this current lack of evidence based research is the modalities main limitation, however this does not detract from its unique ability to provide additional physiological information to the diagnostic process (Soroko and Howell 2018).

Thermography Health and safety

Thermography is non-invasive, does not emit radiation and no contact with the animal is required, so the health and safety implications are minimal, however in the authors experience the horses need an experienced handler and consideration should be given to the potential apprehension of the animal to the equipment especially as sedation effects the reliability of the modality.

Conclusion

Each diagnostic modality has a different set of applications and limitations, recognition of these is what makes them useful (Eddy et al 2001) Selection of the most appropriate modality(s) is essential in achieving a full diagnosis, as lameness diagnosis is a complexed subject, multiple modalities used in conjunction is often what is needed to reach a comprehensive diagnosis (fig.9) (Dyson 2013). Murray (2011) talked about the importance of localisation by diagnostic analgesia before the application of MRI, coupled with the clinical history to ensure any lesions assessed are relevant to the case. Adrian et al (2017) outlined various inter modality relationships utilised to obtain full diagnosis, the use of x-rays to assess bone changes often needing to be coupled with soft tissue diagnostics, and the advantageous coupling of ultrasonography and arthroscopy. Diagnosis is most commonly a multi-step process of elimination, each modality adding to the overall picture (Genovese 1986, Dyson 2013). In the authors opinion, the reoccurring theme with every modality is that correct standardised protocols, clinical image acquisition and experienced veterinary interpretation are all key in their usefulness.


References

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