EQUINE VETERINARY EDUCATION / AE / FEBRUARY 2018
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a)
for bilateral fetlock varus after 140 days of age and some improvement of the deformity still occurred, with one foal achieving acceptable conformation of 0° from a left forelimb varus of 6° and a right forelimb varus of 4°. The other foal failed to respond adequately on one of the limbs; however, in this particular case, the foal was confined to a stall for the duration of implantation due to a concurrent, unrelated lameness. Interestingly, the load-bearing limb corrected to an acceptable angle (from a 7° varus to 1° varus), while the nonweightbearing limb did not (radiographs shown in Fig 3). This is potentially due to a lack of dynamic compressive forces across the physis, which are believed to stimulate physeal growth (Jansson and Ducharme 2005). Many of the foals had a small periosteal reaction at the screw placement site at the time of screw removal; however, in all but one case, this resolved by yearling age. A persistent periosteal reaction remained in one horse and a second surgery to remove the blemish was performed prior to sale at the age of 14 months. A change in technique has been described (Kay and Hunt 2009), which reduces this periosteal reaction. Case series have been reported on the placement of
b)
single transphyseal screws in the distal radius; however, the majority of these focus on correction of carpal varus and offset limbs in older foals and yearling groups (Baker et al. 2011; Carlson et al. 2012). We report on the use of single transphyseal screws placed in the distal radius of foals younger than 2 months. Most authors do not utilise single transphyseal screws in foals younger than one month and alternatively use screw and wire transphyseal bridging or a transphyseal staple. It was previously believed that a single transphyseal screw may cause over-correction of a deviation due to a ‘spot-weld’ of the physis and the rapid growth potential in younger foals (Roberts et al. 2009). The effect of premature closure of the growth plate of the distal radius in young foals would be catastrophic as the distal radius is responsible for 75% of the longitudinal growth of the distal limb (Fretz et al. 1984). In contrast to a transphyseal screw causing a ‘spot-weld’, Kay et al. (2005) report that any transphyseal growth-retarding implant can potentially lead to over-correction of the ALD as a result of over-compression of the physis, leading to physeal dysplasia and cessation of growth, resulting in continued deviation due to collapse of the growth plate. Over-correction of the deformity may require intervention on the opposite side of the limb. Although an uncommon complication, there have also been reported cases of physitis of the distolateral radius after removal of transphyseal screws in older horses, leading to metaphyseal collapse and an angular limb deformity in the opposite direction (Carlson et al. 2012). Levet and Martens (2011) report on two cases of transphyseal screws in the distal radius failing to adequately correct a carpal valgus deformity due to the transphyseal screw pulling out of the epiphysis due to rapid growth at this location, screw sepsis or stripping of the threads; however, we had only one case of screw sepsis in our study. Long-term follow-up after screw removal by personal
Fig 2: Photographs of colt in Figure 1 at time of screw (a) placement and (b) removal. (Note the periosteal and soft tissue reaction at the site of previous hemicircumferential periosteal transection laterally on both limbs, as well as the medial toe extension. This was done by the referring veterinarian prior to presentation, with minimal response).
owner or farm manager communication revealed no over- correction occurring after removal of the screw and excellent cosmetic results in all cases at the time of yearling sales. One foal with bilateral carpal valgus deviations had
radiographic evidence of medial physeal dysplasia at the distal radial physes (Fig 1b). Described treatment for cases such as this is a small transphyseal bone plate and screws
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