From examination to diagnosis
A lameness examination commonly consists of the following stages after initial inspection of the horse:
1. Examination on the straight line: After briefly examining the movement pattern at walk, the horse is assessed for movement asymmetry during trot away from and towards the observer; some veterinarians also inspect the horse from the side, as this allows a better appreciation of limb movement, particularly joint flexion and extension.
2. Examination during trot in a circle, both on a hard and soft surface: Circling is used to exacerbate lameness and allows the detection of bilaterally symmetrical conditions that may not be obvious during assessment on the straight line. A horse that has similar pain in each forelimb or hindlimb will not be able to preferentially unload a specific lame limb so it may appear to move symmetrically (Miller, 1925, Stashak, 2002, Ross, 2011, Buchner 1993). While horses commonly show a more pronounced response to lunging on a hard compared to a soft surface, for certain conditions the reverse can hold true (Ross, 2011).
3. Examination after provocation tests such as flexion tests: Flexion tests are believed to exacerbate pain and consequently movement asymmetry, thus helping to identify the affected limb. However, since flexion tests result in a high number of ‘false positives’ (Keg et al., 1997a, Keg et al., 1997b, Ramey, 1997, Verschooten and Verbeeck, 1997, Busschers and Van Weeren, 2001, Armentrout et al., 2011), they are controversial and regarded with caution by most veterinarians.
4. Manual palpation: Palpation is performed at rest to inspect the horse for visible / palpable abnormalities (swelling, pain response etc.) that may allow identification of the affected region and a preliminary diagnosis. However, palpation does not always reveal detectable abnormalities. Equipment such as hoof testers may also be used.
5. Intrasynovial or perineural analgesia: Local analgesic techniques, commonly referred to as ‘nerve blocks’, are performed in order to localise the lameness within the affected limb. These blocks ‘numb’ specific regions in the horse’s limb; they work based on the principle that once the area which is in pain is anaesthetised, the horse will return to its normal symmetrical movement pattern. These procedures help narrow down the affected region in the limb allowing subsequent diagnostic imaging to be appropriately targeted.
6. Diagnostic imaging: Once the lameness has been localised to a specific region, the region will be investigated using diagnostic imaging (X-ray, Scintigraphy, MRI, CT scans etc) in order to precisely establish the cause of lameness.
Once a diagnosis is made, treatment options and the associated prognosis for recovery can be worked out.
Why visual assessment skills are so important
Evaluation of the horse at trot on the straight line / circle and interpreting the effect of nerve blocks on changes in baseline lameness is commonly considered the most important skill needed to perform a lameness examination on complex cases and “essential for accurate diagnosis” (Ross, 2011a). If the veterinarian is fails to follow a logical diagnostic pathway, the consequences may include misdiagnosis, misdirected treatment, wasted resources and conflicting professional advice, with prolonged lameness as the consequence for the unfortunate horse.
Hence, a key aspect of a successful lameness examination is the accuracy of visual asymmetry assessment during movement, followed by each of the other stages as appropriate. This visual assessment becomes less reliable in cases where lameness is subtle: movement asymmetry becomes very small and is difficult to see. Hence, research has found disagreement even amongst experienced veterinarians on whether lameness is present and which limb(s) are affected (Pleasant et al., 1997, Keegan et al., 1998, Fuller et al., 2006, Hewetson et al., 2006, Keegan et al., 2010, Starke et al. 2013). This means that different veterinarians may further investigate a different limb of a horse, or send the horse home because they do not consider it observably lame.
Armentrout, A. R., Beard, W. L., White, B. J., Lillich, J. D., 2011. A comparative study of proximal hindlimb flexion in horses: 5 versus 60 seconds. Equine Vet J 44, 420-424.
Busschers, E., Van Weeren, P. R., 2001. Use of the Flexion Test of the Distal Forelimb in the Sound Horse: Repeatability and Effect of Age, Gender, Weight, Height and Fetlock Joint Range of Motion. Journal of Veterinary Medicine Series A 48, 413-427.
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Ross, M. W. 2011b. Chapter 7. Movement. In: Ross, M. W. & Dyson, S. J. (eds.) Diagnosis and Management of Lameness in Horses. Elsevier Saunders.
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