How to Place Distal Lateral Radial Transphyseal Screws in a Standing Horse

1. Introduction

Angular limb deformity (ADL), defined as an axial deformation of a limb in a sagittal plane,¹  is common in foals and yearlings and is recognized to predispose lameness and affect performance.^2,3  To enhance sale value and possibly potential performance, excellent conformation is needed.

Angular limb deformity can be presented as either varus or valgus deformity. Varus is defined as a medial deviation of the limb distal to the location of the deformity, whereas valgus is a lateral deviation of the limb distal to the location of the deformity, in a frontal plane. It can originate at different locations of the appendicular skeleton: cuboidal bones of the carpus and tarsus, epiphyses of the long bones, and occasionally in the diaphysis.⁴

Many ALDs correct with conservative treatment, but surgical intervention is recommended in severe cases.^5,6  A demand exists to correct these deviations early in development stage in order to improve cosmetic appeal and potential commercial value. A significant decrease in growth of the distal metacarpus/metatarsus and radial physis occurs after 10 weeks and 15 months, respectively. Distal radial epiphyseal closure occurs at a mean of 24.7 months.⁷ 

Several surgical and nonsurgical techniques have been described in the literature. The first surgical angular limb deformity correction, with temporary transphyseal bridging using staples, was described in 1963.⁸ The majority of the surgical techniques described in the literature report the use of an implant to bridge the convex side or long side of an open physis, at the side of deviation of the affected limb. Transphyseal bridging with staples, single screws, and screws and wires have been used to retard growth of the physis in foals. Single transphyseal screw insertion was first described in 2004.^9,10 Confirming our suspicions, based on our clinical experience, transphyseal screws have recently been shown to be superior to screw and wire, with fewer complications and faster results.¹¹

Transphyseal bridging with a single screw requires only a stab incision and minimal to no dissection of subcutaneous tissue. Hagyard Equine Medical Institute has been using predominantly single transphyseal screws for angular limb deformities since 2004. We have used this technique in the distal metacarpus, metatarsus, radius, and tibia.

In some cases, the risks of anesthesia, financial costs, or the lack of adequate surgical facilities may prevent timely surgical correction of carpal varus deformities. To avoid anesthetic and postoperative anesthetic complications, a standing distal radial transphyseal bridging procedure is a viable option. The purpose of this report is to describe the transphyseal bridging procedure, with a positional single 4.5-mm self-tapping screw, in the lateral aspect of the distal radial physis, in the standing horse.

2. Materials and Methods

Surgical candidates (8 Thoroughbred yearlings) were considered on the basis of clinical evidence of carpal varus deviation that had not corrected with conservative treatment. Visual appraisal alone was used as a standard means of assessment. Standing surgical placement of a lateral transphyseal screw was chosen, based on client’s preference.

Supplies and Equipment

The surgical armamentarium required for standing transphyseal screw placement and removal is the same as required for the procedure under general anesthesia. A small set (Mayo scissors, Brown Adson and Graefe fixation forceps, mosquito hemostatic tissue forceps, and needle holders) is usually required, in addition to the orthopedic armamentarium. To place a 4.5-mm positional self tapping screw, a hexagonal screw driver, 3.2-mm drill bit, soft tissue protector, and power drill is required. Appropriate surgical draping, a 15-T scalpel blade, a balanced electrolyte solution with or without antibiotics, appropriate suture, and bandaging materials should be also at hand.

Intraoperative radiographs are essential for successful screw implantation. It is not necessary for the screw removal procedure unless a broken screw is suspected. The procedure can be performed using appropriate restraint, sedation, and local anesthesia. Stocks are not used for this procedure in our practice.

Perioperative Preparation

Perioperative antimicrobials were administered in the form of procaine penicillin G,^a 22,000 IU/kg intramuscularly and gentamicin sulfate 6.6 mg/kg, intramuscularly. The horses were sedated with detomidine hydrochloride,^b 0.02 mg/kg and butorphanol tartrate^c 0.02 mg/kg, intravenously. Only one dose of sedation is usually required for the duration of the surgical procedure. The skin was clipped, from mid-radius to proximal metacarpus, and aseptically prepared with iodine solution.^d Three to 5 mL of 2% mepivacaine hydrochloride, USP,^e was injected subcutaneously proximally to the incision site (Fig. 1). After two more scrubs after local anesthesia, the surgical site was prepared for surgery.
 

Surgical Procedure

The growth plate was assumed to the widest point of the distal radius. A large Ioban 2^®f was placed around the leg, from the most proximal aspect of the radius. Position of Ioban 2^® was based on surgeons’ preference. A small (1 to 2 cm) skin incision was made 2 to 3 cm proximal to the growth plate, in between the lateral digital extensor tendon and the ulnaris lateralis muscle. The incision was then extended all the way through the periosteum. A 4.5-mm drill bit was then passed through the skin incision and positioned in the periosteal incision. A hole, 3 to 5 mm in depth, was drilled perpendicular to the long axis of the radius (Fig. 2). A 3.2-mm drill bit was passed through the drill guide, and the drill was then angled distally, at approximately 70° (Fig. 3). The tip of the drill bit was inserted about 10 to 20 mm distal to the physis. To ensure appropriate position of the hole, digital radiographs were taken while the drill was still in place. The size of the hole was measured, and a 4.5-mm, self-tapping cortical bone screw was placed with the use of the drill (Fig. 4). In most cases, a 56- to 60-mm, 4.5-mm cortical bone screw was used. The cortical screw was then lightly tightened by hand. Countersinking was not used in the procedure. Skin incisions were closed routinely.

After surgery, antimicrobial therapy was switched to a low dose of sulfamethoxazole/trimthropin 15 mg/kg, PO, twice a day, for 5 to 7 days. Perioperative anti-inflammatory/analgesic therapy consisted of phenylbutazone^g 2.2 mg/kg, q 24 h, PO, for 4 days. [...]