Diagnostic imaging of tendinopathies of the superficial flexor tendon in horses

Tendinopathy of the superficial digital flexor tendon (SDFT) occurs in all types of sport horses and is a common reason for wastage in the racing thoroughbred.1–4 In most clinical cases swelling of the metacarpal or metatarsal area due to tendon injuries is visible and palpable; however, this is very subjective and the severity of the lesion cannot be predicted from the clinical picture.5 After the initial injury, overlapping phases of reactive inflammation, fibroblastic proliferation, remodelling and maturation occur.6,7 These phases can be monitored with the help of grey scale ultrasonographic examinations which are cheap and widely used, with mobile equipment allowing examinations in the stable. During the reactive inflammatory phase, the tendon increases in size and a hypoechoic area of fibre disruption is visible on ultrasonography (Fig 1). This area will fill with blood and debris which appears as heterogeneous hypo- to hyperechoic areas ultrasonographically and cannot always be differentiated from normal tendon tissue. Hence it is sometimes overlooked in transverse images but in longitudinal images the loss of fibre pattern can usually be appreciated. At this stage, an increase in the cross-sectional area (CSA) of the tendon in unilateral cases can be compared to the contralateral limb and an increase of more than 20 per cent is indicative of a tendon injury.8 For bilateral cases, the SDFT:deep digital flexor tendon (DDFT) ratio may be a more sensitive indicator of enlargement than absolute values. Moreover, normal values are published for different types of horses and can be used as a reference.8–12 Fig 1: Transverse (a) …