CROSSTALK: COMBINING DIAGNOSTIC APPROACHES FOR CASE SUCCESS


the primary MRI abnormality frequently did not correlate with the diagnostic anesthetic technique that improved the lameness most.45


• A combination of radiography and ultrasonog- raphy is the first-line imaging protocol for horses with proximal metacarpal/metatarsal pain in order to rule out the presence of obvious bone or joint abnormalities (osteoarthritis and fractures) or severe proximal suspensory desmi- tis. Most frequently, however, the results of these examinations are inconclusive. Especially ultrasonography of the proximal part of the hind suspensory ligament has been reported to result in 66% false positive and 34% false nega- tive findings when compared with high-field MRI.20 A follow-up study that compared ultra- sonography with histology was unable to sup- port the reliability of ultrasonography for the diagnosis of proximal suspensory desmitis.14,15 Of 36 limbs with ultrasonographic evidence of moderate to severe fiber damage to the proxi- mal part of the suspensory ligament, 53% had


no histological abnormalities of the collagen fiber pattern and organization, while 33% had mild and 14% had moderate fiber abnormal- ities. Ultrasonography therefore resulted in a


false positive diagnosis of moderate to severe fiber damage in at least 54% of the suspensory ligaments in this study. The authors described cellular microscopic abnormalities of fibro- blasts, myocytes, and adipocytes in 97% of the suspensory ligaments, but ultrasonography is unable to detect microscopic abnormalities at a cellular level. A significant association was observed between microscopic findings in myo- cytes and ultrasonography, yet the ultrasono- graphic abnormalities described at the outset related to the collagen fiber pattern.14


• Given the limitations of ultrasonography in the di- agnosis of proximal suspensory desmitis (espe-


cially in hindlimbs), it is tempting to propose low- field MRI as an alternative first-line or at least second-line imaging modality for the proximal metatarsal/distal tarsal region. Both the proximal metacarpal/metatarsal and distal carpal/tarsal regions are commonly looked at concurrently dur- ing MRI examinations because it is difficult to localize pain definitively in either one or the other region with diagnostic anesthesia.20,45 However, the interference of motion artefact with image quality, especially in T2 spin echo and STIR images of this region, imposes significant limita- tions on accurate assessment of the soft tissue structures in this region with standing MRI. Unsurprisingly, many clinicians have considered the technique more reliable for the diagnosis of


148 2022 / Vol. 68 / AAEP PROCEEDINGS


osseous abnormalities than of proximal suspen- sory desmitis,46 while results have been more encouraging in forelimbs (Fig. 6).47,48 MR images of the suspensory origin need to be assessed with


caution as motion artifacts (with standing low- field MRI) andthevariableappearanceof the muscle and fat tissue bundles should not be con-


• In view of the problems of motion in low-field


fused with signal changes caused by injury. Low- field MRI may be helpful to identify osseous abnormalities of the tarsal and carpal bones including sclerosis, slab fractures, and osseous cyst-like lesions, but motion artifact may interfere with accurate assessment of osteophytes, chip fractures, and joint space narrowing.


MRI of the proximal metatarsal region, high- field MRI might be regarded as a more suitable second-line imaging modality in hindlimbs.46 It is also a suitable third-line imaging modality if the results of low-field MRI are inconclusive in forelimbs.47


• CT and contrast CT may have certain advan- tages as a third-line imaging modality. It ismore sensitive thanevenhigh-fieldMRI for subtle new bone formation, bone resorption, and avulsion fragments (Fig. 6) associated with the proximal attachment of the suspensory ligament49 because of the lack of contrast between bone and soft tis- sue at the ligament-cortical bone interface onMR images.Moreover, contrast enhancement may be observed in active proximal suspensory desmi- tis lesions but not in chronic fibrosis on CT images.50


The Stifle


• Radiography and ultrasonography are a useful first-line imaging protocol as they provide a reliable


• Both low- and high-field MRI7,51 as well as CT examinations52,53 of the stiflecan now beused as second-line diagnostic modalities for improved di- agnosis of injuries of this complex joint asmany of the soft tissue structures of the joint cannot be evaluated comprehensively with first-line conven- tional imaging modalities. However, general anesthesia is required for these cross-sectional imaging techniques, and current high-field mag- nets impose a size limitation on the horse due to the diameter of the bore. In one low-field MRI studyof 76 sportshorseswith stiflelameness, the prevalence of meniscal lesions was 95%, cruciate ligament injuries 43%, and bone marrow lesions 14%.51 Although these observations suggest that


imaging diagnosis for many conditions causing sti- fle lameness and have offered the traditional basis for further arthroscopic exploration of the joint.


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