Angular limb deformities (ALDs) in the carpus may be congenital or acquired. The distal radial physis along with the distal metacarpal physis contribute limb length approximately 75% and 5%, respectively. Therefore, these two are the most important to growth manipulation (3). Congenital ALDs are frequent in foals and managemental strategies including surgical techniques are well established. Foals with ALD are either a varus (medial deviation distal) or a valgus (lateral deviation) (2). This condition normally improves spontaneously with increasing muscular strength and age. Generally, it is considered that good carpal conformation in newborn foals is a slight valgus (approximately 2-5°) (5,9).

Depending on the severity of the deviation, growth retardation implants can be placed in the distal radius (6). Recently, it is widely accepted that the single screw transphyseal bridging is effective in treating ALD of the fetlock and the carpus (4). However, there has been only a case report of a successful outcome in 40 days following combination of single screw implant and periosteal transection technique for carpal valgus in Korea (10).

In this report we report a successful outcome in 3 weeks for a Thoroughbred foal with unilateral carpal valgus, treated with single screw transphyseal bridging surgery without periosteal transection.

A 5-week old, 110-kg, (male) Thoroughbred foal with a left carpal valgus was admitted to the J&C Equine Hospital (Fig. 1A). Dorsopalmar radiographs confirmed the left carpal valgus and the measured deviation was 14° (Fig. 1B).

Figure 1. (A) Photograph of the carpal valgus of a 5-week old (male) Thoroughbred foal. (B) Radiograph of the dorsopalmar projections confirmed the left carpal valgus (14°). (C) Needle orientation for screw placement and a 4.5-mm self-tapping cortical bone screw placement to bridge the distal radius. (D) Photograph of the patient foal at the time of screw removal. Visual (E) and radiograph (F) follow-up 7 months after screw removal revealing excellent cosmetic outcomes without over-correction. Radiograph of the dorsopalmar projections confirmed the improved left carpal valgus (2°) (F).

The next day this foal was anesthetized in dorsal recumbency with left front foot attached to a horizontal pole for the forelimb to be completely extended. Prior to anesthesia, the patient received flunixine meglumine 1.1 mg/kg IV (Fortis, Dongbang Co., Ltd.; Seoul, Korea), penicillin G procaine 9000 IU/kg and penicillin G benzathine hydrate 6000 IU/kg in combination with streptomycin 12 mg/kg IM (G.C. GPS, Green Cross Veterinary Products Co., Ltd.; Gyeonggi-do, Korea).

Anesthesia was induced with detomidine hydrochloride 0.002 mg/kg IV (Detomidin^®, Provet Veterinary Products Ltd.; Istanbul, Turkey), diazepam 0.03 mg/kg IV (Diazepam inj., Samjin pharm. Co., Ltd.; Seoul, Korea) and ketamine 2.2 mg/kg IV (Huons Ketamine HCl inj., Huons; Seoul, Korea), and was maintained with isoflurane (Ifran^®, Hana Pharm. Co., Ltd.; Gyeonggi-do, Korea) with 100% oxygen for the entire duration of the surgical procedure. Left front limb was clipped from the mid medial radius to the mid medial carpus, aseptically prepared, and draped in a standard fashion.

After surgical preparation, a 20-gauge needle was placed on the drape over the medial aspect of the distal radius to identify the location of drilling end between metaphysis and distal articular surface of radius, and the oblique drilling direction with radiographic confirmation. A 20-mm longitudinal stab incision 35 mm proximal to the distal radial growth plate was made using a scalpel blade (no. 10) through the skin, subcutaneous tissue, and periosteum. The incision was placed at the craniocaudal midpoint of the medial radius. Blunt dissection of the underlying connective tissue was conducted using Metzenbaum scissors. A Weitlaner retractor was placed into the incision to retract the skin and surrounding soft tissues. A 2-3 mm deep 3.2-mm drill hole was made at the incision perpendicular to the axis of radius to prevent slipping when drilling obliquely. Then, a 3.2-mm oblique hole was drilled into the radius towards the needle end location. The hole end location between metaphysis and distal articular surface of radius was double checked radiographically during drilling. The screw length was measured 56 mm by the depth gauge. A 4.5-mm self-tapping cortical bone screw was inserted obliquely with the radiographic confirmation of the direction and location (Fig. 1C). The transphyseal bridge was placed obliquely across the dorsomedial side and ended between the distal radial metaphysis and epiphysis.

The surgical site was rinsed with sterile saline before closure. Subcutaneous tissues were closed with a simple continuous suture pattern using 2-0 synthetic absorbable suture material and the skin was closed using 1-0 non-absorbable suture material with 2 simple interrupted sutures. The surgical incisions were kept under a light bandage for 2 weeks and skin sutures were removed on the 14th day following surgery. During the post-operative period, the foal received flunixine meglumine 1.1 mg/kg IV (Fortis, Dongbang Co., Ltd.; Seoul, Korea), penicillin G procaine 9000 IU/kg and penicillin G benzathine hydrate 6000 IU/kg in combination with streptomycin 12 mg/kg IM (G.C. GPS, Green Cross Veterinary Products Co., Ltd.; Gyeonggi-do, Korea) q24h for 3 days after surgery.

The comfort of the foal was excellent throughout the post-operative period. He was discharged 3 days after surgery. Instructions for rehabilitation included 1 week of complete stall rest, followed by 2 weeks of small paddock turnout following surgery. It was also requested that the foal be closely observed for changes in the degree of valgus deformity and that it be returned for reevaluation and implant removal when the leg had straightened.

Three weeks after single screw transphyseal bridging surgery, the foal was reexamined (Fig. 1D). The radiographic evaluation showed significant improvement of left carpal valgus (2°) compared to the pre-operative radiograph (14°).

The screw removal was made without breakage and the foal was discharged on flunixine meglumine 1.1 mg/kg IV (Fortis, Dongbang Co., Ltd.; Seoul, Korea), penicillin G procaine 9000 IU/kg and penicillin G benzathine hydrate 6000 IU/kg in combination with streptomycin 12 mg/kg IM (G.C. GPS, Green Cross Veterinary Products Co., Ltd.; Gyeonggi-do, Korea) q24h for 3 days and with a recommendation that the limb be bandaged with every other day changes for one week.

When visited at the farm 7 months after discharge for follow up, the foal showed excellent cosmetic outcome both visually and radiographically (Fig. 1E, F).

This report documents the use of single screw transphyseal bridging in a 5-week-old Thoroughbred foal for correction of carpal valgus. There are some researchers of the opinion that ALDs will correct with conservative management alone (7). However, it was shown in a study which tracked horses during the first year of life that 14% of carpal valgus deformities did not self-improve to a desirable conformation (8). For successful surgical intervention, it is important to evaluate deformities that are not improving, or even worsening.

Diagnosis of ALD is based on clinical examination and visual inspection. Radiographs constitute an essential tool to assess affected joints. Dorsopalmar/dorsoplantar projections on long cassettes are required to secure optimal visualization of axes of the long bones inclusive of the affected joint. In the present case, lateromedial radiographs of carpus was also acquired to ensure absence of a craniocaudal bowing of the radius. The decision for early surgical correction herein was made to avoid deteriorating of the carpal valgus during the fast-growth phase.

In this case, the single screw transphyseal bridging technique required 3 weeks to improve the ALD even though the surgery was done without radial disto-lateral periosteal transection. No complications were observed and visual/radiograph follow-up 7 months after screw removal revealed no over-correction after the screw removal. Previously, implantation of a single transphyseal screw with periosteal transection technique for carpal valgus has been described as an effective method for ALDs in foals (10). The result shows that the single screw transphyseal bridging without periosteal transection is an efficient technique for the carpal valgus and appears to provide rapid improvement of the ALD without over-correction.

Some conformations have been shown to adversely affect the athletic performance of racehorses (1). Accordingly, there is pressure on breeders to produce horses with better conformation for the value of individuals in the sales. Based on the case described herein, it is impossible to determine the ideal time frame for the surgical intervention with single transphyseal screw in foals with ALD, however, given the degree of correction of the carpal valgus in the current report, early surgical intervention with the single screw transphyseal bridging technique for carpal valgus treatment in foals should be considered.

Despite the constraints of limited clinical case reports with horses in Korea, this case report supports the previous findings of the single screw transphyseal bridging technique without lateral periosteal transection of distal radius in the literature regarding the efficiency and time required for correction. Although a successful result was achieved in this case, the investigation for an ideal age in association with the outcome of single screw transphyseal bridging in the distal radius would be needed in a greater number of growing horses with ALD.

The authors have no conflicting interests.