EQUINE VETERINARY EDUCATION / AE / AUGUST 2020
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Orthopaedic felt or impression material is placed across
the bulbs of the heels and 2-inch casting tape5 is applied around the perimeter of the foot forming an attachment between the hoof wall, screws and wooden shoe. The casting tape provides circumferential stability that when attached to the screws not only adds security but may decrease flaring of the hoof wall during weight bearing that appears to pull the sole distally (Thomason 2007; O’Grady 2010; Parks and O’Grady 2015). Following application of the wooden shoes, horses are allowed brief periods of controlled exercise according to their comfort level. The exercise can be in the form of hand walking or turn out in a small paddock. Horses are radiographed at 4-5 weeks to assess improvement of the soft tissue structures and the wooden shoes left in place until the desired results are achieved, reset if necessary or transferred to conventional shoes (Fig 11).
Unilateral displacement of the distal phalanx
Unilateral displacement of the distal phalanx in a mediolateral direction commonly occurs because of overloading one side of the foot or from laminitis. Unilateral displacement can occur in two clinical scenarios. The first context is less recognised where one side of the foot is overloaded and the distal phalanx descends. Here, the limb conformation of the horse leads to an asymmetric landing which causes disproportionate loading on one side of the foot. Hoof characteristics would include an offset foot, a sheared heel, compressed growth rings and decreased growth at the coronet above the displaced heel (Fig 12a). In the second scenario, the horse will have clinical signs of laminitis, radiographic evidence of not only displacement or rotation in the dorsal section of the foot but also unilateral displacement of the distal phalanx as noted on the DP radiographic view. The hoof wall on the displaced side of the foot will be thickened compared with the contralateral side due to the diseased lamellae (Sherlock and Parks 2013; Parks and O’Grady 2015) (Fig 12b). Based on the apparent asymmetry of the distal phalanx within the hoof capsule visible on radiographs, a clinician’s first response might intuitively be to try and restore the asymmetry of the distal interphalangeal joint and the position of the distal phalanx in relation to the ground. This would most readily be accomplished by raising the side of the hoof on which the distal phalanx is displaced. However, this practice will increase the weight bearing on the affected side and cause
the distal phalanx to displace further in relation to the hoof capsule, along with increased discomfort. Horses with unilateral displacement show an increased distance between the distal phalanx and the hoof wall on the affected side which indicates weight bearing by the wall on the displaced side would have increased leverage on the hoof capsule, thus potentially shifting the centre of pressure towards the affected side. Theoretically, the hoof capsule can be stabilised in relation to the distal phalanx by increasing weight bearing on the contralateral side and reducing weight bearing on the affected side. Biomechanically, the weight of the horse is opposed by the GRF which is exerted on the foot at every point of contact. The GRF acts on the foot through the COP, therefore, changing the placement of the shoe should effectively change the centre of pressure. The COP is important because it determines the distribution of stresses within the hoof; therefore, changing the position of the wooden shoe will cause an asymmetrical redistribution of pressure on the ground surface of the foot that will change the COP (Fig 13a). The author has been successful in controlling mediolateral displacement by setting the wooden shoe wide on the unaffected side (O’Grady et al. 2007; O’Grady 2010; Parks and O’Grady 2015). The foot is trimmed as described above making sure the
hoof wall and frog are on the same plane and that either the lateral or medial hoof wall is not lowered more than the other. Any significant flare on the affected side of the foot is reduced with a rasp from the outer hoof wall and impression material is placed in the palmar section of the foot to make it load sharing. The wooden shoe is fitted to the foot such that it is flush or tight on the affected side and then forms a 6.3–9.5 mm (1/4–3/8-in) extension beyond the perimeter of the wall on the unaffected side of the foot (O’Grady et al. 2007; O’Grady 2010; Parks and O’Grady 2015) (Fig 13b).
Conclusions
The wooden shoe provides an alternative farriery option when treating a variety of foot problems. Treating many of these foot problems is subjective due to the variations in each case such as chronicity, instability, integrity of the structures of the hoof capsule and hoof conformation. Results from the author’s practice and consulting service during the last 5 years treating acute and chronic laminitis, white line
Fig 11: Radiographs show the conformation of the foot before application of the wooden shoe and the change in the soft tissue structures 4 weeks after application.
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