Treating navicular disease

The key to successful long-term management of ‘palmar foot pain’, which is a clinical sign rather than a diagnosis, is knowledge of the exact nature of the condition, as many different conditions may fall into this category (Labens and Redding, 2012). Treating ‘palmar foot pain’ often involves management of lesions of the navicular apparatus itself but may also involve the distal part of the deep digital flexor tendon, the distal interphalangeal joint and its collateral ligaments, the distal phalanx and the hoof capsule. Advanced diagnostic imaging has definitely deepened our knowledge of the spectrum of pathologies encountered in horses with ‘foot pain’, but it remains challenging to make evidence-based therapeutic decisions for an individual case. Moreover, it should be highlighted that there is no imaging modality able to visualize pain, and therefore, the interpretation of the (abundance of) structural abnormalities identified by advanced imaging still relies on the clinical information including response to diagnostic anesthesia.

The close relationship between form and function of the equine hoof opens unique therapeutic perspectives, and even subtle biomechanical changes created by therapeutic trimming and/or shoeing may be an important and underestimated part of the treatment strategy (Oosterlinck et al., 2017a,b). In the early stages, biomechanical optimization with or even without further medical support may be all that is needed. Moreover, even when medical or surgical treatment is deemed necessary, the complementary effects of trimming and/or shoeing should be considered. This has been described by Oosterlinck et al. (2017a,b) and will therefore not be repeated here.

Intrasynovial injection of anti-inflammatory medication is a cornerstone of the treatment in many cases. Bell et al. (2009) reported that in a sample of 23 horses presented for MRI examination of foot pain, 74% returned to intended use within 2-4 weeks after navicular bursa injection, and mean duration of soundness was 7.3 months. Horses with erosions of the flexor surface of the navicular bone, or with adhesions between the deep digital flexor tendon and the navicular bone responded poorly, whereas cases with navicular bursitis compared to other MRI findings responded very well to treatment. Similarly, in a larger study sample of 101 horses, Marsh et al. (2012) reported that 75% returned to their intended use for a mean of 9.7 months, with the subgroup with lameness less than 6 months before treatment outperforming the group with longer duration of lameness. Rest affected outcome, as 71% of the horses that were immediately returned to work after treatment were able to return to their intended use for a mean of 5.5 months, whereas 84% of horses placed into a 6-month rest and rehabilitation programme after treatment returned to their intended use for a mean of 19 months, which was a significantly larger proportion and a significantly longer time. Horses with bursitis were more likely to return to their intended use than those with scar tissue in the proximal portion of the navicular bursa, adhesions between the deep digital flexor tendon and the navicular bone, or multiple abnormalities. From these studies, it is concluded that identification of specific abnormalities via MRI does affect treatment strategy and prognosis, and that rest and rehabilitation are important, especially in cases with deep digital flexor tendinopathy. However, even within the category of deep digital flexor tendinopathy, the prognosis for different lesions is variable, and it has been shown that dorsal border lesions have a better prognosis than core lesions and sagittal splits of the tendon (Cillan-Garcia et al., 2013). Moreover, lesions size is an important prognostic factor, and one study determined that horses with lesions >35 mm or >20% of the tendon cross-sectional area remained lame (Vanel et al., 2012). Clinically, horses with unilateral lameness respond better to injection than horses with bilateral lameness (Marsh et al., 2012). Results may vary based on the intended use, as horses with tendinopathy of the deep digital flexor tendon within the foot used for Western performance activities seem to respond better than horses used for English performance activities (Lutter et al., 2015). [...]