Diagnosis of Digital Flexor Tendonitis – What’s hot and what’s not?

Superficial (SDF) and deep digital (DDF) flexor tendinopathy are among the leading causes for horses’ early retirement due to the high reinjury rate and the potential to result in performance- limiting lameness. Given the significant advances in the past couple of decades our understanding of the pathophysiological processes has changed [1].

Ageing tendon tissue, subclinical degenerative processes and microdamage form the prelude to more obvious and acute tendinopathies which are easily perceived and diagnosed without imaging technology. A pain response to palpation, presence of abnormal peritendinous tissues or, in advanced cases, the bowed appearance sufficiently localise the injury site. Ultrasonography is then used to describe the injury morphology and establish a baseline against which rehabilitation progress is assessed [2].

In select cases ultrasonography may even aid in the prediction of more serious injury as is the case with peritendinous oedema and an otherwise unremarkable SDF tendon [3]. However, for other conditions such as distal DDF tendinopathy, a clinician’s reliance on advanced imaging technologies to make a diagnosis and provide a prognosis is naturally far greater [4,5]. Therefore, what’s hot and relevant in diagnosing flexor tendonitis is specific to the nature and context of the injury, guiding use of ultrasonography, magnetic resonance or computed tomographic imaging. Improving the detection of early and subclinical disease or differentiating subtle changes in a tendon’s rehabilitation to adjust workloads is associated with significant clinical merit. As such, the future of diagnostic imaging lies in prognostication of subtle changes and prevention of more serious disease.

Ultrasonographic methods that may fulfil this brief are ultrasound tissue characterisation (UTC) and sonoelastography [6,7]. UTC has been demonstrated to allow reliable assessment of tendon integrity based on generation of a 3D data block and post-acquisition computations to establish the pixel stability across images [8,9]. Sonoelastography produces a visual representation of the tendon tissue’s compression stiffness which is interpreted in the context of tissue healing and maturation (hard tissue – chronic, established scar; soft tissue – acute disruption, absence of structural components) [10-12].

Further clinical exploration is needed to establish the significance of UTC or sonoelastographic changes. Furthermore, development of strain-based rather than compression-based elastographic measures is needed to better capture the normal loading pattern and resulting deformation of flexor tendons.

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