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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 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 ’ 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

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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 . If the limb is deviated medially a crush have been described (Caron 1988). In the carpus 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 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

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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 et al. 2006). Recently, heavy birth weight are taken on long cassettes with the foal standing as has been associated with a tendency towards offset ‘square’ as possible. The site of bisection of 2 lines drawn carpi (Santschi et al. 2006). Although linear methods for down the centre of the long bones represents the so- evaluation of conformation have been described called pivot point and determines the site of angulation (Holmstrom et al. 1990; Magnusson 1990; Mawdsley et al. (Caron 1988). In this manner change in angle at a physis 1996) equine conformation is most commonly evaluated can be differentiated from that occurring through a joint. subjectively with its inherent advantage of assessing the Asymmetric epiphyseal growth in the absence of individual in 3 dimensions (Love et al. 2006). The authors concurrent disproportional physeal growth may also be perform an evaluation with the foal at rest (static noted (Leitch 1985; Jansson and Ducharme 2005) (Fig 4). evaluation) and when walked towards and away from Finally changes in angle through the carpus (possibly as a the observer (dynamic evaluation). Static evaluation is result of collapse or hypoplasia) may be evident. Studies performed 1 or 2 m in front of the foal in line with the have shown that the latter 2 conditions are also amenable ‘face’ of the carpus. This eliminates the rotational to management through growth retardation at the component of a deformity, so that any further deviation is adjacent physis (Brauer et al. 1999). Hindlimb radiographs in attributable to angular deformity alone. Dynamic the frontal plane are less valuable as the tibia and cannon- evaluation is valuable in assessing the influence of bone are not in alignment through the tarsus (Auer 1991; change in angle on limb carriage and weightbearing. Dutton et al. 1999). Radiographs of long bones also help Surgery is avoided on a foal that displays a normal limb determine diaphyseal growth abnormalities. Dependent on flight and tracks true. Unless an obvious deformity is their severity, these aberrations may require aggressive present at rest, surgery would have the potential to disrupt ‘resetting’ of the long axis of the limb, through osteotomies this flight pattern and is therefore not indicated. In or ostectomies. These deformities preclude an athletic contrast development of a varus deformity of the fetlock career and will not be discussed further here.

Fig 4: Fetlock varus in a 4-day-old foal. Note that the asymmetric Fig 3: Bilateral hindlimb tube casts in a foal with tarsal crush. epiphyseal growth is the cause of the deviation in this case. EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 5

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An understanding of growth plate physiology and exercise and regular hoof trimming (every 2–4 weeks). A pathophysiology is important in understanding the large number of minor deformities will respond to this rationale behind treating angular limb deformities treatment alone (Slone et al. 2000; Read et al. 2002; Greet originating at or adjacent to the physis. Endochondral and Curtis 2003). Trimming of the feet is believed to be ossification and the resultant longitudinal bone growth most effective in improving frontal plane abnormalities at represents a progression of cells from the resting zone of the fetlocks. However, carpal deviations may also result in the physis, through the proliferative zone into the zone of abnormal hoof growth and wear. Therefore frequent maturation, resulting in calcification (Fretz 1980; Ballock balancing of the foot is necessary. In the case of valgus and O’Keefe 2003). The latter 2 zones are particularly deformity the lateral wall of the hoof should be trimmed. susceptible to compressive forces (Fretz 1980). Under With varus deformities the inside will be shortened. In all normal circumstances disproportionate and intermittent cases squaring of the toe will facilitate break over at the loading of the physis stimulates growth, leading to a centre of the foot. Trimming should be done in moderation natural correction of deviations (Frost 1994). Persistent, and attempts should be made to enhance a larger solar excessive forces, however, result in retardation of surface by mild rasping of the heels (Greet and Curtis ossification and thickening of the cartilaginous growth 2003). To avoid excessive trimming and encourage correct plate, which will eventually transition to a region of weightbearing composite extensions may be used. These inactive necrosis and fibrosis (Rooney 1969; Fretz 1980). This must be applied carefully as creation of a fulcrum with the in turn will lead to exacerbation of the underlying acrylic may result in coffin bone fracture or excessive deviation. Firth et al. (1988) was able to show that the distal stresses on the joints of the phalanx. Avoiding the metacarpus is loaded asymmetrically with compressive formation of an abrupt ledge when moulding the acrylic forces acting medially. The excessive loading through this will prevent this. Incorporation of fibreglass strands into the aspect of the leg in high birth weight foals may explain the acrylic may improve its longevity. Caution should be association between increased weight and varus fetlock exercised against excessive application of composite deviation (Santschi et al. 2006). Recent studies of growth materials due to their potential to compromise the integrity plate physiology and pathophysiology in the horse appear of the hoof wall. Controlled exercise (limited, if any to be lacking. paddock turn-out) will reduce continued compression of a The alignment of a horse’s limb at birth is genetically compromised physis (Greet 2000). predetermined, but is also influenced by further factors Surgical means of growth manipulation include growth such as the health of the mare (e.g. placentitis) as well as acceleration or growth arresting procedures. Growth her nutritional status. Management practices will continue acceleration is not solely reliant on longitudinal growth at to influence conformation until the cessation of growth. A the physis and can, therefore, be used repeatedly, foal that stands crooked will unevenly distribute pressure although it seems to be most effective in younger foals. across its physes. Similarly a foal fed a diet rich in energy The risk of incisional and cosmetic complications does, will not only load its limbs excessively but is also at risk of however, increase with repeated procedures. At a young developing physitis. These factors alone will alter the rate age the thick inner layer of periosteum, known as the of endochondral ossification. To further complicate cambium, is at its most productive. This explains the matters pain secondary to physitis can elicit an avoidance success of early intervention (Rackard and Bellenger stance creating continued disproportionate pressure in 2004). Growth arresting procedures are reliant on residual the region of the growth plate (Hunt 2000). From this it is longitudinal development at the physis and, therefore, clear that angular limb deformities are the result of a bring about change most rapidly at the times of rapid number of influences (Fretz 1980). Success of intervention is longitudinal growth (i.e. during growth spurts). The timing dictated by degree of angulation as well as the remaining at which surgical intervention needs to occur is based on growth potential. Surgery should be reserved for cases with quantitative analysis of the growth of long bones in the severe deviations (greater than approximately 12–15º), horse, determining when functional closure of the physes those that are not responding to conservative measures or occurs (Fretz et al. 1984). These principles are still largely those that are showing deterioration (Mitten and Bertone applicable, though recent studies have shown an ability, 1994; Hunt 2000). in individual cases, to correct deviations somewhat later in life (Witte et al. 2004; Kay et al. 2005; Hunt 2006) (Table 1). Treatment of acquired deformities Growth acceleration The treatments discussed in the current paper all have poor scientific evidence for effect; however, they are The value and technique of growth acceleration through established practices in equine veterinary medicine. As local periosteal transection, was first described in horses in more evidence-based studies are performed their the early 1980s (Auer and Martens 1982; Auer et al. 1982). efficacy may begin to be questioned. Since that time the technique of hemicircumferential Conservative management in the neonate and during periosteal transection and elevation (HCPTE) has been the first few months of the foal’s life involves controlled widely used. Early results gave a good prognosis for EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 6

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soundness irrelevant of angulation, location of pivot point The study shows no effect of the HCPTE procedure and or changes noted in the carpal bones (Fretz and Donecker suggests that the apparent straightening of the limb 1983; Bertone et al. 1985a,b). A later study assessing the represents an optical illusion resulting from the blemish success of Thoroughbred foals showed that foals affected created by surgery on the concave aspect of the limb. It by deviations at multiple sites were less likely to perform as might, however, be argued that the model involving well as those which were affected at only one site. Also the creation of angular limb deformities does not reflect the response seen at the distal radius was better than that same physiological and pathological changes as seen in achieved at the distal cannon bone (Mitten et al. 1995). clinical cases. Both authors use HCPTE and have seen As the name suggests the procedure involves incision of improvement in an adequate number of cases in order to the periosteum adjacent to the physis (on the concave justify its continued use. It is, however, important to bear in aspect of the limb) and its elevation. More detailed mind that the effect of this procedure may be transient, in descriptions of the technique are available in a number of particular if an underlying condition goes unrecognised or general equine surgery texts (Auer 1991, 2006). The is not addressed. An example is the foal with offset carpi, procedure has recently come under closer scrutiny and an which secondarily develops varus deformity and only unequivocal mechanism has yet to be established. Early temporarily improves following HCPTE. investigation showed that circumferential transection of the periosteum in chicken radii lead to longitudinal growth Growth arrest (Crilly 1972). Crilly speculated that transection releases the tension at the growth plates, concurrently enhancing The principle behind temporary arrest of growth is simple longitudinal growth. It was surmised that the tension present and relies on mechanical restriction. The physis is bridged causes compression at the physis, which results in inhibition on the convex side of the limb, compressing and inhibiting of chondrocyte proliferation (Ballock and O’Keefe 2003; the cells of the physis (Bramlage 1999) thereby arresting Rackard and Bellenger 2004). This theory was initially growth until the limb is straight, at which time the implant adopted in order to explain the success of HCPTE in foals is removed. Initial descriptions of transphyseal bridging (Bertone et al. 1985b; Caron 1988; Bramlage 1999). More used staples across the physis (Carlson et al. 1972). Since recent studies suggest that the fibrous periosteum lags then screws, placed on either side of the growth plate behind the longitudinal growth of the bone, negating this and linked by a stainless steel wire in figure-8 fashion were first theory, as shown by Bertram et al. (1998) in an avian utilised and believed to be of superior cosmetic outcome model. Whether the increased vascular supply associated (Fretz et al. 1978). More recently a single screw crossing with surgical intervention is relevant to perceived the physis has been used (Witte et al. 2004; Kay et al. 2005; longitudinal growth remains to be seen (Rackard and Hunt 2006). Permanent bridging (epiphysiodesis) has been Bellenger 2004). Histological evaluation has shown a concern. A rabbit model studying the relative size of drill increases in the number of hypertrophic cells in the proximal hole injury necessary to cause growth disturbance growth plate following unilateral circumferential incision of determined that 7–9% of the physis had to be disrupted in the periosteum of the tibia in rats (Taylor et al. 1987). Further order for this to be a risk (Garces et al. 1994; Janarv et al. investigations have targeted the influence of transection on 1998). A further study creating 1 mm drill tracts across the proliferation of chondrocytes under the control of a rat femoral physes and evaluating them at intervals up to local feedback loop primarily involving 3 signalling 16 weeks showed no significant difference in the length or molecules synthesised by growth plate chondrocytes: growth plate height between drilled holes and their parathyroid hormone-related peptide (PTHrP), Indian controls. Histologically the drill holes filled with bony hedgehog (Ihh) and transforming growth factor-beta (TGF- trabeculae and appeared to increase in width over time, β). This feedback loop regulates the rate at which growth suggesting that eventual epiphysiodesis may be possible plate cells leave the proliferative zone of the physis and (Garces et al. 1994). Finally, a study in dogs, assessing the irreversibly commit to being terminally differentiated histological effects of surgical trauma at the physis, hypertrophic cells (Ballock and O'Keefe 2003). determined that the amount of growth retardation was Clinically this procedure has come under attack. Read proportional to the size of the cancellous bone bridge et al. (2002) created an experimental blinded study that connected the epiphysis to the metaphysis. comparing the HCPTE procedure and a sham procedure. Longitudinal growth did, however, continue in the injured

TABLE 1: Period of rapid growth, age at radiographic physeal closure and average age at which correction using a single screw was successful

Age at radiographic Average age at which Period of rapid growth physeal closure correction using a single screw Location of growth plate (months) (months) was successful (months)

Distal metacarpus/metatarsus 0–3 6–15 3 Distal radius 0–8 22–36 12 Distal tibia 0–6 17–24 7 EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 7

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epiphyseal plate despite the presence of a bridge implant. These problems are avoided through close (Campbell et al. 1959). monitoring of change in conformation as well as Permanent physeal bridging from the presence of the assessment of the activity at the physis. If physeal dysplasia implant resulting in overcorrection has not been clinically does occur, aggressive anti-inflammatory medication and substantiated. One author’s impression is that if rest will generally minimise its effect. Failure at the screw overcorrection occurs it may be a result of excessive head is associated with technique of screw placement physeal compression resulting from the speed of and its removal. The initial description using a lag screw correction using this technique. Physeal dysplasia may also technique (Witte et al. 2004) has since been replaced result in continued ‘correction’ after removal of the with position screw placement, yielding adequate compression across the physis for satisfactory results (Hunt 2006). The single screw has been described in use at the distal tibia, the distal radius and the distal cannon bone (Witte et al. 2004; Hunt 2006) (Figs 5 and 6). Results of its use in a large number of horses have been described (Kay et al. 2005). A 4.5 mm cortical screw of appropriate length is used at all locations. The second author makes an exception in foals aged <8 weeks, in which a 3.5 mm screw is used at the distal cannon bone. Screws at all locations should be placed to maximise perpendicular transection of the physis. Care is taken when placing the screw at the distal metacarpus or metatarsus not to cross midline (i.e. the contralateral side of the sagittal ridge) distal to the physis. The screw should aim to be within the lateral fourth of the physis. Countersinking maintains a normal contour to the limb, but may result in the need for removal of bone over the screw head on its retrieval. On the other hand a lack of countersinking carries with it the risk of screw head bending in particular when a severe deviation is being addressed. Altering the angle of the drill at the outset of drilling can provide adequate room for seating the screw head. Poor follow-up may result in over-correction, which intuitively places excessive stress on the screw head. Fig 5: Radiographic confirmation of single screw placement on the lateral aspect of the distal radius correcting a varus deformity. Results evaluating the use of a single screw have shown more rapid correction of deviations (Fretz and Donecker 1983; Witte et al. 2004; Kay et al. 2005; Hunt 2006). Cosmetic complications include thickening or the growth of white hairs at the site of surgery. Complications jeopardising soundness or even survival include incisional infections, bandage sores and implant failure (Hunt 2006). The majority of infections result from bandage sores associated with pressure necrosis over a bony prominence or the screw head. For this reason horses should be discharged with detailed instructions on bandaging techniques. While the single screw is applicable in the majority of instances, other techniques still have their place. In foals, for example, the second author prefers the use of staples on the medial aspect of the distal radius as these seem to achieve better purchase in the soft bone. Others preferentially implant screw and wires in the same location during periods of epiphysitis in weanlings and yearlings.

Fetlock deviation

Deviations at the fetlock must be monitored closely as the Fig 6: Radiographic confirmation of single screw placement on the time for intervention is limited to the first 3–4 months of life. medial aspect of the distal tibia, correcting a valgus deformity. At this time the distal cannon-bone physis functionally EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 8

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closes and with it the opportunity for correcting Carpal deviation abnormalities. Varus deviation of the forelimbs, presenting as pigeon Carpal valgus deviations of 2–5º are normal (Auer et al. toe is common. Young foals with upright conformation will 1982; Mitten and Bertone 1994; Greet and Curtis 2003) and generally improve given time. If noted in combination with the overall condition of the horse must be taken into offset knees or carpal valgus, a varus deformity at the consideration (Greet 2000). A foal with a narrow chest fetlock may warrant intervention (Fig 7). The latter is evaluated early, for example, may present with apparent achieved through periosteal transection and elevation at moderate carpal valgus deformity. The same foal several an early age (3–4 weeks) (Greet 2000). Foals that are weeks later, however, will gain weight, expand its chest and heavy bodied, fine boned and stand base wide appear to improve the appearance of the abnormality (Greet 2000). be particularly prone to this problem. While early Early intervention in this instance is not indicated. In a management may appear to have been successful, subjective evaluation of conformation in Thoroughbreds continued diligent monitoring is necessary in order to from foals to yearlings, Santschi et al. (2006) determined appreciate any regression in conformation later in life. gradual correction in carpal valgus. Heavier bodyweight Should this occur transphyseal bridging is indicated (Greet appeared to be correlated with a lack of self-correction in 2000; Hunt 2000), again in a timely fashion (at 8–12 weeks) this study. Dynamic gait evaluation may predict an (Fretz and Donecker 1983). Recent results on the use of a impending deviation. In the case of carpal valgus the foal single screw at the distal cannon bone physis report that adopts a predictable ‘sweeping’ pattern of flight to the the implants were placed at an average age of lower limb, landing consistently on the medial aspect of the approximately 3 months. These implants were left in place hoof wall and causing excessive wear. Severe carpal valgus for an average of 1.5 months (Kay et al. 2005). This is deformity (>12–15º) will need attention and may initially be consistent with a previous report that showed long bone addressed through medial, distal radial HCPTE (at age 8–12 growth ceases at age 4 months (Fretz et al. 1984). Fetlock weeks) and if necessary later through temporary, lateral varus of the hindlimbs is relatively common and should not growth arrest. Carpal varus is noted less frequently in young be overlooked. Early intervention with HCPTE may preclude foals but may result from excessive loading of a support limb the need for implants. Fetlock valgus is less common and (Greet 2000). Repeat evaluation maximises the likelihood of often self limiting with improved condition (Greet 2000). self-limiting correction following weaning, whilst still allowing Valgus deformity of the metacarpophalangeal joint has, sufficient time for correction of the deviation before growth however, been shown to be detrimental for jump racing ceases. A report on the use of transphyseal bridging of the performance (Weller et al. 2006b) and should therefore be distal radius showed an average age at implant placement addressed if present and severe. of approximately 12 months (with a maximum age of

Fig 8: Tarsal crush. The acute change in angle at the dorsal tarsus pinches the cuboidal bone cartilage, causing crushing of the Fig 7: Carpal valgus and fetlock varus in a young foal affecting the dorsal aspect of the third tarsal bone. This is a deviation in the right forelimb. Surgical intervention involved HCPTE at the lateral sagittal plane, but concurrent changes in the frontal plane distal radius and medial distal cannon bone right front. (generally valgus deformities) often also result. EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 9

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18 months) and duration of placement of approximately 40 Tarsal deviation days (Kay et al. 2005). Approximately 70% of the implants were placed in order to correct varus deformities of the These deviations are generally valgus deformities. A study carpus, underscoring the significance of this deviation at assessing the influence of conformation on injuries in late weanling age. National Hunt horses showed an increase in pelvic fracture and digital flexor tenosynovitis associated with tarsal valgus a) b) (Weller et al. 2006b). A lateral to medial radiographic view of the tarsus is indicated in order to assess for concurrent tarsal bone collapse (Fig 8). The frequency with which these processes occur together has been described as 56 and 73% (Dutton et al. 1998, 1999). Successful outcome through use of HCPTE is enhanced through young age at treatment. Foals aged <60 days had a significantly better outcome than older foals. It is also dependent on the presence and degree of concurrent tarsal crush. In general approximately 50% of foals with tarsal deformities can be expected to fulfil owner’s expectations with regard to athleticism (Dutton et al. 1999). Results of placement of a single screw for acquired angular deviations (without evidence of tarsal crush) support the suggestion that growth retardation techniques are more effective than growth acceleration in the tarsus (Dutton et al. 1999; Witte et al. 2004). The foals of the latter study were an average age of 7 months at the time of implant placement and screws were left in for an average of 2 months. All animals responded to treatment and achieved improved if not desired conformation (Witte et al. 2004). The authors avoid the use of a single screw in the tarsus of foals due to the soft nature of the bone of the medial malleolus. In making a decision for management at the tarsus the observer must remember that an angle of approximately 5–7º is Fig 9a: Tarsal varus of the right hind due to trauma sustained on the medial aspect of the distal tibia. The radiograph (b) shows the accepted as being normal (Auer 1991). Tarsal varus is pivot point at the distal tibial physis and a change in angle of 11º. usually trauma related (Greet 2000) (Fig 9). Management was attempted in this 12-month-old colt through placement of a single screw in the lateral malleolus of the distal tibia. The procedure brought about minimal change in angle.

Fig 11: Offset or bench knees in a young foal. The medial aspect of the carpus sustains excessive loading, which may result in a varus Fig 10: Severe rotational abnormality of the left carpus and fetlock. deformity. EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 10

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Combined deviations Manufacturer’s address

While considering the ‘correctness’ of each joint 1Equine Bracing Solutions, Trumansburg, New York, USA. individually helps the inexperienced observer in initial assessment, it is an oversimplification and management References must be initiated in the context of the entire limb. Deviation Anderson, T.M. and McIlwraith, C.W. (2004) Longitudinal development in one location may be offset by an alteration elsewhere in of equine conformation from weanling to age 3 years in the the limb. Use of geometric evaluation alone is misleading. Thoroughbred. Equine vet. J. 36, 563-570. Often carpal valgus deformity is accompanied by fetlock Anderson, T.M., McIlwraith, C.W. and Douay, P. (2004) The role of valgus. Serial evaluation is acceptable in this instance as conformation in musculoskeletal problems in the racing progressive correction of carpal angulation will often Thoroughbred. Equine vet. J. 36, 571-575. improve the conformation at the fetlock. On the other Auer, J.A. (1983) Angular limb deformities in foals: Part 2. Developmental factors. Comp. cont. Educ. pract. Vet. 5, 27-35. hand, if the fetlock is correct in the frontal plane, or even Auer, J.A. (1989) Beitrag zur Fruehdiagnose und Behandlung einer varus in nature, simply observing correction of a concurrent speziellen Stellungsanomalie beim Pferd. Pferdeheilkunde 5, 201-205. carpal valgus may result in inward rotation of the ipsilateral Auer, J.A. (1991) Angular limb deformities. In: Equine Medicine and fetlock. With the limited time available at the fetlock, early Surgery, 5th edn., Vol. 2, Eds: P.T. Collahan, I.G. Mayhew, A.M. Merritt recognition is vital. An understanding of such interactions and J.M. Moore, American Veterinary Publications, Goleta. pp will improve the likelihood of a desirable outcome. 1691-1693. Wind swept foals represent a combination of limb Auer, J.A. (2006) Angular limb deformities. In: Equine Surgery, 3rd edn., Eds: J. Auer and J. Stick, W.B. Saunders, Philadelphia. pp 1130-1149. deformities that have been brought in association with in utero positioning (Auer 1983; Leitch 1985; Greet 2000). Auer, J.A. and Martens, R.J. (1982) Periosteal transection and periosteal stripping for correction of angular limb deformities in foals. Am. J. Initially coaptation for laxity is important (using stout vet. Res. 43, 1530-1534. bandages centred over the tarsus). The remaining angular Auer, J.A., Martens, R.J. and Williams, E.H. (1982) Periosteal transection deviations, due to discrepant growth at the physis, are for correction of angular limb deformities in foals. J. Am. vet. med. addressed at a later date taking care not to miss the Ass. 181, 459-466. appropriate time for intervention at the fetlock (Greet Ballock, R.T. and O'Keefe, R.J. (2003) The biology of the growth plate. J. Bone Joint Surg. Am. 85, 715-726. 2000). Bertone, A.L., Park, R.D. and Turner, A.S. (1985a) Periosteal transection and stripping for treatment of angular limb deformities in foals: Further abnormalities radiographic observations. J. Am. vet. med. Ass. 187, 153-156. Bertone, A.L., Turner, A.S. and Park, R.D. (1985b) Periosteal transection Rotational abnormalities (Fig 10) and stripping for treatment of angular limb deformities in foals: clinical observations. J. Am. vet. med. Ass. 187, 145-152. These should not be confused with changes in the frontal Bertram, J.E., Polevoy, Y. and Cullinane, D.M. (1998) Mechanics of plane. These deviations will not respond to conservative or avian fibrous periosteum: tensile and adhesion properties during growth. Bone 22, 669-675. surgical intervention (Greet 2000; Greet and Curtis 2003). Bramlage, L.R. (1999) The science and art of angular limb deformity Attempts can be made to gradually ‘derotate’ the limb correction. Equine vet. J. 31, 182-183. through the use of commercially available braces (Frank Brauer, T.S., Booth, T.S. and Riedesel, E. (1999) Physeal growth Foal Easy Splint)1. In this construct a twister cable attaches retardation leads to correction of intracarpal angular deviations as to a shoe and is secured to a harness around the withers. well as physeal valgus deformity. Equine vet. J. 31, 193-196. Gradual corrective forces are applied by adjusting the Campbell, C.J., Grisolia, A. and Zanconato, G. (1959) The effects torque on the cable. produced in the cartilaginous epiphyseal plate of immature dogs by experimental surgical traumata. J. Bone Joint Surg. Am. 41, 1221-1242. Offset knees, bench knees (Fig 11) Carlson, R.L., Lohse, C.L., Eld, L.A. and Hughbanks, F.G. (1972) Correction of angular limb deformities by physeal stapling. Modern This deviation is not desirable. In the young foal it has the vet. Pract. 53, 41-42. potential to cause focal physeal compression and Caron, J.P. (1988) Angular limb deformities in foals. Equine vet. J. 20, associated deviation (Jansson and Ducharme 2005), and 225-228. may later predispose to splint bone fracture. Most recently Crilly, R.G. (1972) Longitudinal overgrowth of chicken radius. J. Anat. 112, 11-18. it has been correlated with metacarpophalangeal joint Dutton, D.M., Watkins, J.P., Honnas, C.M. and Hague, B.A. (1999) disease in the racehorse (Anderson et al. 2004). While Treatment response and athletic outcome of foals with tarsal valgus carpal valgus may self-correct over the first year of life, the deformities: 39 cases (1988-1997). J. Am. vet. med. Ass. 215, 1481- incidence of off-set knees appears to increase in the same 1484. time-frame (Santschi et al. 2006). This deformity has been Dutton, D.M., Watkins, J.P., Walker, M.A. and Honnas, C.M. (1998) approached as a combination of a valgus deformity at the Incomplete ossification of the tarsal bones in foals: 22 cases (1988- 1996). J. Am. vet. med. Ass. 213, 1590-1594. distal radius and a varus deformity of the proximal cannon Firth, E.C., Schamhardt, H.C. and Hartman, W. (1988) Measurements of bone and recommendations for growth promotion or bone strain in foals with altered foot balance. Am. J. vet. Res. 49, retardation are made accordingly (Auer 1989). 261-265. EVE 08-062 Witte:Layout 1 11/06/2009 12:07 Page 11

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Fretz, P.B. (1980) Angular limb deformities in foals. Vet. Clin. N. Am.: Magnusson, L.E.A.T. (1990) Studies on the conformation and related Large Anim. Pract. 2, 125-150. traits of the Standardbred Trotters in Sweden. J. anim. Breed Genet. Fretz, P.B., Cymbaluk, N.F. and Pharr, J.W. (1984) Quantitative analysis of 107, 135-148. long-bone growth in the horse. Am. J. vet. Res. 45, 1602-1609. Mawdsley, A., Kelly, E.P., Smith, F.H. and Brophy, P.O. (1996) Linear Fretz, P.B. and Donecker, J.M. (1983) Surgical correction of angular limb assessment of the Thoroughbred horse: an approach to deformities in foals: a retrospective study. J. Am. vet. med. Ass. 183, conformation evaluation. Equine vet. J. 28, 461-467. 529-532. Mclaughlin, B.G., Doige, C.E., Fretz, P.B. and Pharr, J.W. (1981) Carpal bone lesions associated with angular limb deformities in foals. Fretz, P.B., Turner, A.S. and Pharr, J. (1978) Retrospective comparison of J. Am. vet. med. Ass. 178, 224-230. two surgical techniques for correction of angular deformities in foals. J. Am. vet. med. Ass. 172, 281-286. Mitten, L.A. and Bertone, A.L. (1994) Angular limb deformities in foals. J. Am. vet. med. Ass. 204, 717-720. Frost, H.M. (1994) Wolff's Law and bone's structural adaptations to mechanical usage: an overview for clinicians. Angle Orthod. 64, Mitten, L.A., Bramlage, L.R. and Embertson, R.M. (1995) Racing 175-188. performance after hemicircumferential periosteal transection for angular limb deformities in Thoroughbreds: 199 cases (1987-1989). Garces, G.L., Mugica-Garay, I., Lopez-Gonzalez Coviella, N. and J. Am. vet. med. Ass. 207, 746-750. Guerado, E. (1994) Growth-plate modifications after drilling. J. Pediatr. Orthop. 14, 225-228. Rackard, S. and Bellenger, C. (2004) Periosteal surgery: a review of clinical and experimental findings. Vet. Comp. orthop. Traumatol. 2, Greet, T.R. (2000) Managing flexural and angular limb deformities: the 57-63. Newmarket perspective. Proc. Am. Ass. equine Practnrs. 46,130-136. Read, E.K., Read, M.R., Townsend, H.G., Clark, C.R., Pharr, J.W. and Greet, T.R. and Curtis, S.J. (2003) Foot management in the foal and Wilson, D.G. (2002) Effect of hemi-circumferential periosteal weanling. Vet. Clin. N. Am.: Equine Pract. 19, 501-517. transection and elevation in foals with experimentally induced Holmstrom, M., Magnusson, L.E. and Philipsson, J. (1990) Variation in angular limb deformities. J. Am. vet. med. Ass. 221, 536-540. conformation of Swedish Warmblood horses and conformational Rooney, J.R. (1969) Chapter 11. Biomechanics of Lameness in Horses, characteristics of elite sport horses. Equine vet. J. 22, 186-193. Williams and Wilkins, Baltimore. pp 127-128. Hunt, R.J. (2000) Management of angular limb deformities. Proc. Am. Santschi, E.M., Leibsle, S.R., Morehead, J.P., Prichard, M.A., Clayton, Ass. equine Practnrs. 46, 128-129. M.K. and Keuler, N.S. (2006) Carpal and fetlock conformation of the Hunt, R.J. (2006) New techniques in transphyseal bridging. Proceedings juvenile Thoroughbred from birth to yearling auction age. Equine of the American College of Veterinary Surgeons Symposium. pp vet. J. 38, 604-609. 168-169. Slone, D., Roberts, C. and Hughes, F. (2000) Restricted exercise and Janarv, P.M., Wikstrom, B. and Hirsch, G. (1998) The influence of transphyseal bridging for correction of angular limb deformities. transphyseal drilling and tendon grafting on bone growth: an Proc. Am. Ass. equine Practnrs. 46, 126-127. experimental study in the rabbit. J. Pediatr. Orthop. 18, 149-154. Taylor, J.F., Warrell, E. and Evans, R.A. (1987) The response of the rat tibial Jansson, N. and Ducharme, N. (2005) Angular limb deformities in foals: growth plates to distal periosteal division. J. Anat. 151, 221-231. causes and diagnosis. Comp. cont. Educ. pract. Vet. 26, 48-55. Weller, R., Pfau, T., May, S.A. and Wilson, A.M. (2006a) Variation in Kay, A., Hunt, R., Pe, T., Ma, S. and Rodgerson, D. (2005) Single screw conformation in a cohort of National Hunt racehorses. Equine vet. transphyseal bridging for correction of forelimb angular limb J. 38, 616-621. deviation. Proc. Am. Ass. equine Practnrs. 51, 306-308. Weller, R., Pfau, T., Verheyen, K., May, S.A. and Wilson, A.M. (2006b) The Leitch, M. (1985) Musculoskeletal disorders in neonatal foals. Vet. Clin. effect of conformation on orthopaedic health and performance in N. Am.: Equine Pract. 1, 189-207. a cohort of National Hunt racehorses: preliminary results. Equine vet. Love, S., Wyse, C.A., Stirk, A.J., Stear, M.J., Calver, P., Voute, L.C. and J. 38, 622-627. Mellor, D.J. (2006) Prevalence, heritability and significance of Witte, S., Thorpe, P.E., Hunt, R.J., Spirito, M.A. and Rodgerson, D.H. (2004) musculoskeletal conformational traits in Thoroughbred yearlings. A lag-screw technique for bridging of the medial aspect of the distal Equine vet. J. 38, 597-603. tibial physis in horses. J. Am. vet. med. Ass. 225, 1581-1583, 1548.

1600 8.0 16.0 24.0 32.0 NADA 140-973, Approved by FDA VEntIpULmIn Syrup may cause undesirable reactions. Clenbuterol, like other beta adrenergic agonists, can 1700 8.5 17.0 25.5 34.0 produce significant cardiovascular effects in some 1800 9.0 18.0 27.0 36.0 Ventipulmin® Syrup people as evidenced by elevated pulse rate, blood (clenbuterol HCl) Administer two treatments per day. pressure changes and/or ECG changes. Directions for Administration: Remove safety cap For use in horses not intended for food Dosage and Administration: Administer orally twice a and seal; replace with enclosed plastic dispensing day (b.i.d.). Initial dose is 0.5 mL/100 lbs body weight Each mL contains Clenbuterol HCl 72.5 mcg cap. Remove cover from dispensing tip and connect (0.8 mcg/kg) twice daily. syringe (without needle). Draw out appropriate volume Caution: Federal (U.S.A.) law restricts this drug to use Dosage Schedule: of VEntIpULmIn Syrup. Administer orally to the horse. by or on the order of a licensed veterinarian. Initial dosage: administer 0.5 mL/100 lbs (0.8 mcg/kg) Replace cover on dispensing tip to prevent leakage. Federal (U.S.A.) law prohibits the extralabel use for 3 days (6 treatments); precaution: the safety cap should be placed on the of this drug in food animals. If no improvement, administer 1.0 mL/100 lbs bottle when not in use. Description: Clenbuterol (4-amino-alpha-[(tert- (1.6 mcg/kg) for 3 days (6 treatments); Adverse Reactions: mild sweating, muscle tremor, butylamino) methyl]-3, 5-dichlorobenzyl alcohol If no improvement, administer 2.0 mL/100 lbs restlessness, urticaria and tachycardia may be hydrochloride) is a beta-2-adrenergic agonist which (3.2 mcg/kg) for 3 days (6 treatments); observed in some horses during the first few days of provides bronchodilating properties as well as other If no improvement, horse is non-responder to treatment. may cause elevated creatine kinase (CK) effects, with minimum effect on the cardiovascular clenbuterol and treatment should be discontinued. serum levels. Ataxia was observed in 3 out of 239 system. It is provided as a colorless, palatable syrup. horses (1.3%) in clinical studies. VEntIpULmIn Syrup (clenbuterol hydro-chloride) is Recommended duration of treatment at effective dose How Supplied: VEntIpULmIn Syrup is available antagonized by beta-adrenergic blocking agents. is 30 days. At the end of this 30-day treatment period, in 100 mL and 330 mL plastic bottles containing drug should be withdrawn to determine recurrence of indications: VEntIpULmIn Syrup (clenbuterol 72.5 mcg clenbuterol HCl per mL. hydrochloride) is indicated for the management of signs. If signs return, the 30-day treatment regimen may be repeated. If repeating treatment, the step-wise Storage: Store at controlled room temperature horses affected with airway obstruction, such as occurs (15-30°C) (59-86°F). Avoid freezing. in chronic obstructive pulmonary disease (COpD). dosage schedule should be repeated. Contraindications: VEntIpULmIn Syrup antagonizes Dosage Calculation Chart mL/treatment mL/treatment mL/treatment mL/treatment the effects of prostaglandin F2 alpha and oxytocin. VEntIpULmIn Syrup should not be used in pregnant Lbs. Body at 0.5 mL/100# at 1.0 mL/100# at 1.5 mL/100# at 2.0 mL/100# abcd mares near term. Because tachycardia may occur, Weight (0.8 mcg/kg) (1.6 mcg/kg) (2.4 mcg/kg) (3.2 mcg/kg) VEntIpULmIn Syrup should not be used in horses 500 2.5 5.0 7.5 10.0 suspected of having cardiovascular impairment. 600 3.0 6.0 9.0 12.0 Warning: the effect on reproduction in breeding 700 3.5 7.0 10.5 14.0 stallions and brood mares has not been determined. 800 4.0 8.0 12.0 16.0 treatment starting with dosages higher than the initial 900 4.5 9.0 13.5 18.0 dose is not recommended. 1000 5.0 10.0 15.0 20.0 1100 5.5 11.0 16.5 22.0 Human Warnings: this product is not for human use 1200 6.0 12.0 18.0 24.0 or for use in animals intended for food. Keep out of 1300 6.5 13.0 19.5 26.0 the reach of children. In case of accidental ingestion, 1400 7.0 14.0 21.0 28.0 contact a physician immediately. Ingestion of 1500 7.5 15.0 22.5 30.0

If no improvement, administer 1.5 mL/100 lbs (2.4 mcg/kg) for 3 days (6 treatments);