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after birth will often improve a severe flexural deformity enough to allow splinting or bandaging until the condition fully resolves (Hunt 2011, 2012; Caldwell 2017). The less common variation of a flexural deformity that
occurs in neonates is an isolated unilateral deformity of the DIPJ and does not correct with manual extension applied to the joint. The deformity occurs in all degrees but is often severe and difficult to manage. Again, toe extensions are not beneficial and typically cause the foal to stumble. Although it is difficult to apply, useful external coaptation to this area, articulating extension braces attached to a foot cuff, application of a cast or application of a flexible tension band with surgical tubing will provide appropriate mechanics to this region (Hunt 2012; Caldwell 2017).
Acquired flexural deformities Acquired flexural deformities (AFD) involving the DIPJ are generally noted when the foal is between 2 and 4 months old and generally involves the DIPJ initially. It is commonly a unilateral condition but occasionally affects both forelimbs. The aetiology of this deformity is unknown, but speculative causes include genetic predisposition, improper nutrition (i.e. overfeeding, excessive carbohydrate [energy] intake, unbalanced minerals in the diet) and excessive exercise (Adkins 2008; Hunt 2011; O’Grady 2012, 2017; Caldwell 2017). A study looking at grazing patterns in a small number of foals showed that foals with long legs and a short neck tended to graze with the same limb protracted (van Heel et al. 2006). Fifty percent of the foals in this study developed mis-matched feet with a higher heel on the protracted limb leading the researchers to feel there may be a possible correlation between conformational traits and an acquired flexural deformity. It is the author’s opinion that a large contributing factor to this syndrome is contraction of the muscular portion of the musculotendinous unit caused by a response to pain (Kidd and Barr 2002; Caldwell 2017). The source of such pain could be discomfort anywhere along the distal limb, including physeal dysplasia or trauma causing foot pain in foals exercising on hard ground. Rapid weight gain in the foal may result in physeal overload and pain. Discomfort may follow aggressive hoof trimming where excessive sole is removed, thus rendering the immature structures within the hoof capsule void of protection and prone to bruising (O’Grady 2012, 2017). The foal then becomes unwilling to bear full weight on the affected feet. Any discomfort or pain in the foot or lower portion of the limb coupled with reduced
weight-bearing on the affected limb appears to initiate a flexor withdrawal reflex; this causes the flexor muscles proximal to the tendon to contract, leading to a shortened musculotendinous unit and an altered position of the DIPJ. This shortening of the musculotendinous unit shifts weight- bearing to the dorsal section of the foot causing inflammation of the lamellae in dorsal hoof wall, increased load on the dorsal sole, bruising of the sole, hoof wall separations, reduced hoof wall growth of the dorsal aspect of the hoof wall and excessive hoof wall growth at the heel to compensate for the shortening. As the flexural deformity may be secondary to pain in these cases, it is essential that possible sources of pain should be carefully identified and localised by physical examination and, if necessary, by regional analgesia and diagnostic imaging. The possibility of a genetic component should also be considered for
acquired flexural deformities, as some mares consistently produce foals that develop a flexural deformity in the same limb as the dam or grand dam in which a similar deformity is present (Hunt 2012; Caldwell 2014; O’Grady 2017). It also appears that many individual foals have a propensity to acquire a flexural deformity as a group of foals can be fed the same ration, maintained in the same environment, have the same farriery and exercise routine yet only the odd foal will develop a flexural deformity (O’Grady unpublished data, 2012).
Mild acquired flexural deformities of the DIPJ The initial clinical sign of a mild flexural deformity of the DIPJ may only be abnormal wear of the hoof at the dorsal toe, which is often discovered by the farrier during routine hoof care. Closer or subsequent investigation may reveal that the dorsal hoof wall angle is increased, a prominent coronary band may be present but the heels of the hoof capsule are still on the ground. However, after the heels of the hoof capsule have been trimmed to an appropriate length, the heels may no longer contact the ground. Most foals affected to this degree may already have a mildly broken forward hoof-pastern axis. Increased palpable digital pulse, heat in the affected foot and signs of pain may be noted when small hoof testers or even thumb pressure is applied to the solar aspect of the toe dorsal to the frog are not uncommon clinical findings. Hoof tester pain is generally due to lack of sole thickness, trauma and excessive weight-bearing on the dorsal toe. A recent method of classifying flexural deformities of the DIPJ using a grading system (Grade 1–4) has been proposed (Redden 2003). It is always beneficial to classify the severity of the flexural deformity to devise an appropriate treatment plan and monitor the response to a given therapy. It also becomes a useful part of the foal’s record. Conservative treatment such as restricting exercise to
reduce further trauma to the foot is paramount. Correcting the nutritional status of the foal (i.e. weaning the foal to avoid possible excessive nutrition from the lactating mare and/or decreasing carbohydrate intake), administering an anti-inflammatory agent (NSAID) to relieve pain, administering oxytetracycline to foals with acquired flexural deformities to facilitate muscle relaxation and carefully trimming the palmar section of the hoof are, in the author’s opinion, is a reasonable starting point. The NSAIDs should be administered short-term and judiciously in foals due to the potential side effects, such as gastroduodenal irritation and nephrotoxicity. For analgesia, the author will administer firocoxib (0.1 mg/kg bwt q. 24 h) or flunixin meglumine (1.1 mg/kg bwt q. 24 h) combined with a gastric protectant. Hoof trimming is directed towards improving the hoof angle by lightly trimming the heels from the middle of the foot palmarly until the hoof wall at the heels and the frog are on the same plane. Over trimming of the heels should be discouraged as this will invariably cause the heels to lift off the ground which can be noted on firm footing. The bars can be thinned in this instance as an attempt to spread and possibly improve heel expansion. Additionally, the heels of the hoof capsule adjacent to the frog sulci may also be rasped to a 45° angle in an attempt to promote spreading. If the sole thickness is sufficient in the dorsal foot (does not deform with hoof testers or thumb pressure), breakover is moved palmarly by creating a mild bevel with a rasp, which begins just dorsal to the apex of the frog and extends to the perimeter of the dorsal aspect
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