IN-DEPTH: THE RELATIONSHIP BETWEEN IMAGING FINDINGS AND LAMENESS


proximomedial tibia at the medial femorotibial joint, are often identified in sound horses. Furthermore, studying the influence of these changes on perfor- mance is difficult. Qualitative imaging features in addition to clinical information should be utilized to assess the finding(s). For example, proximal third metatarsal osteoproliferation may be at the joint mar- gin (e.g., osteophyte), slightly distant from the joint margin (likely associated with the dorsal tarsometa- tarsal ligament), or more distant from the joint margin (likely associated with the cranial tibial tendon and/or peroneus tertius insertion). If the osseous prolifera- tion is present at the joint margin, close evaluation for subchondral bone change (irregularity or change in opacity) or other evidence of joint disease should be undertaken. Additional abnormalities will lead to a stronger conclusion of the significance of the finding. Marginal proliferation on the proximal, medial tibia may provide evidence of joint disease. This can prompt the observer to closely inspect the medial femoral condyle for shape change or alteration in structure, the attachment sites of the menisco-tibial or cruciate ligaments, or prompt further investigation with additional radiographic projections (e.g., flexed lateral oblique [cranio 5 disto 10 lateral-caudoproximo- medial oblique] to highlight the medial femoral con- dyle) or ultrasound. Enthesophytes provide clear evidence of chronic pathologic change at the bone/soft tissue interface. Certain locations are very fre- quently identified and likely carry limited significance, for example the oblique sesamoidean ligaments or the proximal attachment of the distal digital annular lig- ament. Because these findings can occur at such a wide variety of locations for a wide variety of reasons, each case should be evaluated on an individual basis. When a bone spur is identified, it should be care-


fully categorized as an osteophyte distant from the joint surface, periarticular (joint margin) osteo- phyte, or enthesophyte (tendon/ligament/joint cap- sule insertion). The categorization of the lesion will then prompt either active dismissal of the le- sion as insignificant, further investigation of the lesion, or allow the observer to make a diagnosis.


5. Osteochondrosis


Osteochondrosis lesions come in all shapes and sizes, and should include lesions of endochondral ossification that develop in juvenile horses. A more inclusive term of juvenile osteochondral conditions19 has been proposed to include osteochondrosis, juve- nile subchondral osseous cyst-like lesions, physitis, and avulsion lesions of epiphyseal or apophyseal bone. Many studies evaluate the influence of lesion size, location, surgical versus medical management and the influence on outcome.1,20–26 Overall, the understanding of these conditions is much greater in horses used for racing than other non-racing disciplines. In general, osteochondrosis increases the likeli-


hood of untoward downstream effects including sy- novitis and osteoarthritis. The identification of an


26 2020  Vol. 66  AAEP PROCEEDINGS


osteochondrosis lesion should prompt an immediate assessment of multiple factors that include the le- sion size and depth, the relationship to the weight bearing surface and/or other articular components, the presence of other associated joint abnormalities such as soft-tissue swelling or osteophyte formation, and surgical accessibility. The identification of ad- ditional, related lesions or contralateral lesions likely increases the clinical significance of lesions in the individual animal.


6. Cervical Spine


High-quality radiographs of the cervical vertebrae provide a wealth of information about vertebral morphology.27,28 Quality assessment should be performed by the operator at the time of image ac- quisition. Patient positioning and preparation, beam angle, film focal distance, exposure, and mo- tion all play a role in image quality that can signif- icantly detract from the clinical utility of radiographs. Latero-lateral radiographs have sev- eral limitations including superimposition of the bone over the soft tissues of the spinal cord and articular process joints, a lack of orthogonal projec- tions, and that they are generally taken with a fixed or stationary head position. These limitations can be partially alleviated through quantification of the sagittal diameter ratios, the use of oblique and/or positional projections and complementary imaging techniques such as ultrasound, and the use of con- trast media (myelography). Thoughtful consider- ation of the limitations and their respective solutions should enter into the clinicians’ rationale early in the discourse. When quantification of sag- ittal diameter ratios and myelography are em- ployed, it is important to remember that even these techniques are faulted. Inter- and intra-observer variability in ratio measurement make the use of this technique somewhat questionable except in very positive or very negative cases.3 Similarly, myelography, though for a time considered to be the gold standard for the identification of spinal cord compression, is fraught with false-negative and false-positive results. Even with these limitations, radiographs are still useful for the evaluation of the shape, size, alignment, symmetry, opacity, and number of vertebrae giving good information about many disease processes. Ultrasound is invaluable for the assessment of the vertebral surfaces and associated soft tissues, and for its role in ultrasound-guided or ultrasound- assisted interventions. In general, ultrasound does not provide useful information for the assessment of the central nervous system. Nerve-root evaluation can be performed when the nerve roots or lower motor neurons exit the vertebral canal. Evaluation of the nerve roots can be performed in the lumbosa- cral region on per-rectal ultrasound examination providing some information about these structures. Ultrasound is complementary to radiographs for evaluation of the nuchal ligament and bursa, artic-


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