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EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 2 378 EQUINE VETERINARY EDUCATION / AE / July 2009 Review Article A review of angular limb deformities S. Witte* and R. Hunt† Fethard Equine Hospital, Kilnockin, Fethard, County Tipperary, Ireland; and †Hagyard Equine Medical Institute, 4250 Iron Works Pike, Lexington, Kentucky 40511, USA. Keywords: horse; angular limb deformity; valgus; varus; growth retardation; growth acceleration Summary directed at determining their true effect on incidence of injury. Anderson et al. (2004) correlated the conformation This article provides some guidelines for the evaluation of 115 3-year-old flat racehorses with injury and found that and management of angular limb deformities in young offset knees contributed to fetlock problems and some horses. It begins by looking at factors that influence degree of carpal valgus was protective, with carpal conformation and that should be taken into consideration fracture being less prevalent in its presence. Weller et al. when making a decision as to the significance of a (2006b) found that carpal and tarsal valgus in National particular conformational trait. Perinatal and acquired Hunt horses actually increased the incidence of superficial deformities are then discussed separately with an digital flexor tendon and pelvic injury, respectively. emphasis on the latter. Options for their correction are Occupation must, therefore, factor into interpretation of described as well as the results of recent publications conformational traits. using these techniques. Finally the approach to Bone growth and the resulting changes in management of deformities at each of the most conformation is a dynamic process, continuing until commonly encountered locations is described. physeal closure occurs. Knowledge of the course a conformational trait is likely to take is helpful in determining Introduction its significance. Anderson and McIlwraith (2004) evaluated the conformation of Thoroughbreds, from weanling to age With a wealth of well-bred horses to choose from, a 3 years. Amongst other findings, they describe carpal prospective buyer searches for the horse with ideal conformation changing progressively from ‘back-at-the- conformation. The ultimate goal should be long-term knee’ to slightly ‘over-at-the-knee’ over the course of the soundness and assessment of conformation should take 3 year period. They suggest that one might, therefore, both performance and longevity into consideration. The avoid horses that are ‘over-at-the-knee’ at an early age. most conformationally correct horse is not necessarily the Remaining growth potential should factor into the best in this regard, and pedigree appears to be of management of deformities. greater significance (Love et al. 2006). This recent study The definition of ideal conformation obviously requires assessing musculoskeletal conformational traits in further investigation. In the interim, manipulation to achieve desirable appearance will continue and Thoroughbred yearlings was able to show only a weak questions concerning its ethics will linger. In support of association with subsequent racing performance. surgical intervention Bramlage (1999) suggests that if we When assessing conformation, breed specific traits are to question its validity, should we not also be critiquing should be taken into consideration. Standardbred trotters, selective breeding and farriery practices? It is important to for example, naturally show an outward rotation of remember that the involvement of the equine practitioner both the fore- and hindlimb, while Warmblood and should not be restricted to the correction of abnormalities Thoroughbred horses typically only show outward deviation alone. The authors suggest that if a disproportionately of the hindlimb (Holmstrom et al. 1990; Magnusson 1990). large number of foals in a crop are in need of surgery, the A straight limb confirmation is more typical of the National attending veterinarian should be reviewing that farm’s Hunt Thoroughbred (Weller et al. 2006a). breeding and management practices. It is also important Conformational abnormalities have been recognised to bear in mind that attempted correction of and addressed for many years. Recent attention has been abnormalities often depends on the commitment to the risks of general anaesthesia and the potential *Author to whom correspondence should be addressed. complications of surgical intervention. EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 3 EQUINE VETERINARY EDUCATION / AE / July 2009 379 For convenience, angular limb deformities are often A history of pre- or dysmaturity or twin foals warrants classified as those evident immediately following birth particular attention, and radiographic evaluation of the (perinatal abnormalities) and those that only develop as cuboidal bones of the carpus and the tarsus is indicated. the horse ages (acquired deformities). The term angular Crushing of the cartilaginous precursors to these bones will limb deformity has universally been accepted in the field of lead to a change in angle and the relative rapid onset of equine medicine as being synonymous with a deviation in significant and generally debilitating arthritis. The diagnosis the limb when viewing the horse from the front or rear, i.e. is most readily made on the dorsal to palmar view of the in the frontal plane (Mitten and Bertone 1994). In the case carpus and the lateral to medial view of the tarsus (Dutton of a lateral deviation, distal to a reference point, we refer et al. 1999). Typical changes seen with carpal and tarsal to a valgus deformity. If the limb is deviated medially a crush have been described (Caron 1988). In the carpus varus deformity is present. This classification contrasts with this ranges from subtle incongruity at the articular surface, those abnormalities evident when viewing the horse in the resulting from metacarpal or carpal bone collapse or sagittal plane, which include flexural deformities as well hypoplasia (Fig 1) (Bertone et al. 1985a), to obvious as ‘back-at-the-knee’ conformation and laxity through the deformation of the carpal bones (Fig 2). Once the digit. Deciding on a course of action requires knowledge of diagnosis has been made, prognosis is dependent on the physeal physiology, activity of the growth plate and time of degree of change (Dutton et al. 1999) and coaptation is closure. Often multiple sites are affected in one limb and the key to limiting damage. Coaptation may take the form individual variation is great. Development of these of a bilaterally placed stout bandage, use of a dorsal splint deviations is a continuous process so close monitoring and or application of a tube cast. Periarticular ligamentous re-evaluation is paramount to a satisfactory outcome (Hunt laxity is a further reason for perinatal changes in angle. 2000). Again familiarity with farm management and the Palpation of the limb forms the basis of this diagnosis and genetics involved is vital for success. an ability to straighten and manually correct an angular limb deformity supports ligamentous laxity as the cause. Perinatal deformities Treatment is conservative and consists of appropriate rest and limited support (bandages) to protect the limbs and During the perinatal period (usually within the first 2 weeks facilitate ligamentous strengthening. Dependent on the of life) the examiner must be aware of deviations location of the deviation, incorporation of the phalanges resulting from causes other than those associated with into the stabilisation should be avoided in order to prevent disproportionate growth at, or adjacent to, the exacerbation of laxity (Fig 3) (Fretz 1980). Close monitoring physis. Various factors in the history may predispose a foal of the limb for bandage sores and the need for regular to perinatal conformational problems although adjustments due to rapid growth are important epidemiological research into their cause is lacking. considerations (Fretz 1980; Auer 1991). Fig 2: Carpal crush. Note the characteristic lateral collapse Fig 1: Incongruity of the articular surface of the radiocarpal joint as (primarily affecting the 4th carpal bone) and associated valgus a result of distal displacement of the 4th metacarpal bone (most deformity, a reflection of the medial to lateral progression of carpal commonly affected) (Mclaughlin et al. 1981; Bertone et al. 1985a). bone ossification (Caron 1988; Jansson and Ducharme 2005). EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 4 380 EQUINE VETERINARY EDUCATION / AE / July 2009 Acquired deformities or the carpus may only become evident when a foal initially tracks true and later shows a base narrow gait. Acquired angular limb deformities result from Finally foals allowed extensive exercise will tire and may disproportionate longitudinal bone growth and will be the appear conformationally weaker if assessed towards the focus of the remainder of this review. Evaluation of the end of their turn out period. dam and sire may give some indication as to the likely Radiographs of the limb are helpful in not only result if nature is allowed to take its course (Santschi et al. confirming the location of the deviation but also provide 2006). Genetic predisposition and trauma are strongly objective values for the degree of angulation (Fretz 1980; associated with deformities as are physeal dysplasia, Bertone et al. 1985a; Jansson and Ducharme 2005). They nutritional imbalances, infection, exercise and physeal are most useful when assessing forelimb deviations. Films overload (Love