Podiatry Proceedings From Our Practice to Yours 2019 11th Annual NEAEP Symposium Table of Contents Shoeing For Sport Horse Injuries: My Point Of View Pg 3 What’s Going on Back There? A Unique Look at The Back Of The Hoof Pg 7 Trimming the Hoof Capsule to Improve Foot Structure & its Function Pg 17 Navicular Syndrome: Questions Needing To Be Asked Pg 32 Maybe It’s a Nerve Pg 44 New Developments In Our Understanding Of What Causes Different Forms Of Laminitis Pg 49 Hoof Capsule Trimming to Improve the Internal Foot of Navicular Syndrome Affected Horses Pg 54 Evidence-Based Approaches to Treatment and Prevention of Laminitis Pg 66 Trimming Practices Can Encourage Decline In Overall Foot Health Pg 69 A Practical Approach to a Therapeutic Shoeing Prescription Pg 72 Power Point Presentations for this program can be found online at www.theneaep.com/members-only . The password to access this section is: “neaep2019” 2 www.theneaep.com Shoeing For Sport Horse Injuries: My Point Of View Professor Roger K.W. Smith MA VetMB PhD FHEA DEO ECVDI LAAssoc. DipECVSMR DipECVS FRCVS Dept. of Clinical Sciences and Services, The Royal Veterinary College, Hawkshead Lane, North Mymms, Hatfield, Herts. AL9 7TA. U.K. E-mail: [email protected] Synopsis ‘No foot no horse’ is a well-known statement that sums up the importance of the fore (and hind) foot in equine lameness and performance. This presentation will focus on what this presenter considers the most important biomechanical principles in his practice of treating foot-related injuries in sports horses. Introduction Corrective farriery is rarely completely effective without other concurrent treatments although individual horses vary in their response to therapeutic shoeing, and so can be remarkably effective in some. There is considerable variation on what is advised for corrective farriery with a wide array of therapeutic shoes available to the practitioner and many of these shoes work best for the person who first invented them. It is therefore important to work with the farrier to achieve the desired result. If the aim is to change (improve) the foot balance, it can often take at least 2-3 rounds of trimming and shoeing before a beneficial effect on the foot balance can be achieved. Consideration should be given to sound biomechanical principles and use repeat radiography to assess whether the correction of foot balance is being achieved. Roles for therapeutic shoeing - For managing foot problems – o Navicular disease – correction of dorsopalmar foot balance o Solar/distal phalanx bruising – thin soles - For protecting tendons and ligaments - For managing fractures Managing foot problems This requires the following approach: a) Accurate diagnosis. Achieving this will necessitate localizing the lameness to the foot and then undertaking diagnostic imaging to identify the pathology. Radiography may be sufficient (eg for advanced navicular disease and fractures of the distal phalanx and navicular bone) but will often require more advanced imaging, such as MRI, to identify more subtle causes of lameness, including soft tissue pathology of the foot. Ultrasonography can be used through the three ultrasound ‘windows’ (dorsal coronary band; between the heels, and transcuneal) but there are still considerable limitations to this imaging modality compared to MRI. b) Assessment of foot balance Assessment of foot balance should be done both visually and radiographically. Visual appraisal should be from all directions (dorsal, lateral, palmar/plantar, and solar) 3 www.theneaep.com and should be interpreted in the light of the conformation of the rest of the limb. Foot pastern axis (FPA) assess the relationship between the pastern and the foot conformation and is usually only assessible visually because the foot is usually raised on a block for lateromedial radiography which can distort the FPA. Visual appraisal is thus still important to perform first and will inform the interpretation of radiographic foot balance. Mediolateral hoof balance is, in this author’s opinion, a less important parameter than dorsopalmar foot balance. This is because it is strongly influenced by the conformation of the rest of the limb (carpal and fetlock valgus/varus; base narrow versus base wide stance) and by the dynamic aspects of foot placement (landing lateral versus medial) which makes simple recommendations for changing fraught with the risk of exacerbating the problem. In contrast, dorsopalmar foot balance is less influenced by upper limb conformation has a strong influence on the loading of the navicular bone and deep digital flexor tendon1,2. Navicular disease is believed to be the consequence of aberrant remodeling associated with mechanical overload which is exacerbated by the positive feedback loop that occurs when the horse has pain in the heels that induces increased tension in the DDFT in the first half of the stance phase3. The most important parameter for unloading the DDFT and navicular bone is the solar angle of the distal phalanx – for every one degree increase in the downward angulation of the distal phalanx there is a 4% reduction in the peak force exerted by the DDFT on the navicular bone2,4,5. The other dorsopalmar foot balance parameters assessed include the position of the centre of rotation of the distal interphalangeal joint which should be within the middle third of the weight bearing surface of the foot, and the height (length) and angle of the dorsal wall and heels. In addition, the thickness of the sole has strong implications with respect to solar (and distal phalangeal) bruising and corrective farriery (see below). Shoeing for specific foot conditions 1) Navicular disease and DDFT pathology – trimming and shoeing to correct dorsopalmar foot balance This is achieved by preserving the heels while trimming the sole at the toe to improve the downward angulation of the distal phalanx within the hoof capsule. This is only possible when there is a thick enough sole with which to achieve this alteration in angle. If the case of thin soles, artificial elevation of the heels is achieved with wedges or a graduated shoe. This has the same effect in unloading the DDFT but tends to unload the heels which can encourage heel collapse and so should only be used temporarily. The branches of the shoe should be extended as far caudally as possible (to centre the centre of rotation of the distal interphalangeal joint), the toe shortened (dumped), and a shoe with a rolled toe fitted to ease break-over. Suitable shoes would be wide-webbed seated out shoes, natural balanced shoes or egg-bar shoes. 2) Solar/distal phalangeal bruising This injury is most commonly associated with thin soles and shoeing strategies aim to protect the sole through the use of protective soft materials that cover the sole to a greater or less extent. Rim pads offer some protection but leave a large part of the sole open. A wide array of modern packing materials can be used to cover the sole, usually with a pad 4 www.theneaep.com that covers the entire sole. This provides excellent protection of the sole but they can, in themselves, causes solar bruising if too firm. Simple ‘corns’ (bruising of the medial heel; often caused by delayed trimming of overlong foot and reshoeing) can been treated with a short period of time unshod and foot trimming or with a shoe with the end of the medial branch of the shoe seated out on the ground surface of the shoe. 3) Sheared heels Instability of the heels results in one heel being pushed proximally compared to the other. A simple bar shoe, with trimming of the heels of the ‘higher’ heel can be effective at matching heel height and restoring stability. Protecting tendons and ligaments Traditionally egg-bar shoes or shoes with good palmar extension have been advised to ‘protect’ the suspensory ligament (and distal sesamoidean ligaments) although the former has been associated with increased strains in the suspensory ligament5. More recently, shoes with increased width at the toe compared to the heels (see figure 1) have been suggested as being effective in soft ground to increase the load in the DDFT (by the heels sinking in more than the toe) and thereby reduce the loading in the suspensory ligament (and superficial digital flexor tendon) via the extra support provided to the fetlock by the increased tension in the DDFT. However, studies to try and show this effect have been somewhat variable5,6. Nevertheless the biomechanical principle appears plausible and this author uses this approach in hindlimbs but not forelimbs because of the worry of initiating overload of the navicular region. Asymmetric branches of the shoes have also been advised to protect the injured collateral ligament with a wider branch on the side of the injury when the horse is exercising on soft ground (see figure 1). The wider branch does not sink in as far which has the effect of tilting the foot to reduce strain in the injured collateral ligament. Again, this biomechanical principle seems sound and this author advises these shoes when a horse with a diagnosis of asymmetric desmitis of the collateral ligaments of the distal interphalangeal joint returns to work after the initial period of rest to allow the ligament to heal. The deep digital flexor tendon and soft tissues of the navicular region can also be unloaded by raising the heels, either with trimming, wedges or a graduated shoe (see above). Managing fractures of the distal phalanx (and navicular bone and sidebone) In order to minimise movement at the fracture site, prevention of hoof expansion under weight-bearing load is minimised by using a bar shoe with multiple quarter clips. A rim shoe is more difficult to fit effectively and so supplementing the bar shoe with casting tape around the hoof capsule only should offer better immobilisation, although a large retrospective study did not identify any relationship of hoof immobilisation to outcome7.