Chapter 149 Dorsal Thoracic and Lumbar Simple Hook-Rod, Wire, and Wire-Rod Techniques

The first internal fixation device was designed by Harrington in 1947, a period in which the number of patients with poliomyelitis-induced scoliosis was growing, and there was dissatisfaction with the current management of corrective casting. The device was designed to correct scoliotic curvatures and halt progression of cardiopulmonary compromise in affected patients. Initial attempts consisted of screw fixation of facet joints in the corrected position. The results appeared promising, but early beneficial results were short-lived. Facet screw failure led to the development of a hook-and-rod construct, in which hooks were attached to the dorsal elements and held in place with a combination of distraction and compression forces. The clinical results of Harrington’s new system were published in 1962.¹^–³

The Harrington system offered the first internal fixation device for the correction of scoliotic deformities. The system was quickly adopted by spine surgeons and applied to various conditions, including trauma, neoplastic disease, fixed deformities, and degenerative disorders.^2,^4,⁵

The Harrington system, although versatile, was plagued with inherent problems. The system was limited in its design, which allowed for only two points of fixation. Failure at any single hook site led to failure of the entire system.⁶ However, the system has been modified over the years.

In the early 1970s, Luque was faced with an impoverished community in which postoperative bracing was impossible. From these circumstances arose the concept of segmental spinal instruumentation. The Luque system consisted of straight, L-shaped, or rectangular rods attached to lamina via sublaminar wires.⁷ The advent of segmental spinal instrumentation addressed the main problem associated with the Harrington system that had only two points of fixation. Initially, sublaminar wires were used to supplement the Harrington system.⁴^–⁶ This innovation was followed by interspinous wiring techniques, such as Wisconsin wires and Dummond buttons. The original Harrington rod was rigid and difficult to contour, and the rounded caudal rigid tip failed to prevent rotation. This shortcoming led to the development of the square-ended Moe rod, which allowed rod contouring. The three-pointed bending force, which a contured rod provides, was enhanced further by the development of the Edward sleeve.^6,⁸ The Harrington system, although often replaced by newer universal spinal instrumentation systems, can be used to stabilize thoracic and lumbar fractures that result from axial loading and in which the anterior longitudinal ligament is intact.

Harrington Distraction Fixation

Technique

The patient is placed in the prone position, with a midline incision made to expose at least three levels above and two levels below the lesion. A subperiosteal dissection is performed and is carried laterally over the transverse process. The upper hook site is prepared after satisfactory exposure. Typically, this site is located three levels above the injury site, and the inferior facet is exposed at this level. The caudal tip is amputated with either a 1⁄4-inch osteotome or a small Kerrison rongeur. The caudomedial margin of the lamina and underlying ligamentum flavum are excised.

The lamina is conformed to allow seating of the rostral ratcheted hook, typically a no. 1253 hook. A no. 1251 hook can be used as a starter hook, which can be replaced by a no. 1253 hook, a keeled hook, or a bifid no. 1262 hook. The hook is inserted to follow the angle of the facet joint and is gently tapped into position. A well-seated hook should lie orthogonal to the spine (Fig. 149-1). The caudal hook site is generally located two levels below the level of the injury. The interlaminar region at this level is enlarged with a Kerrison rongeur. The ligamentum flavum is excised, and the rostral margin of the lamina is conformed to accommodate the caudal hook, usually a no. 1254 round-hole hook or a no. 1201 square-hole hook (Fig. 149-2). Square-hole caudal hooks are most commonly used because they allow contouring of the rods and minimize rotation. A construct undergoing distraction is depicted in Figure 149-3.

FIGURE 149-1 Harrington fixation, upper hook site. A, Preparation; B–D, insertion.

FIGURE 149-2 Harrington fixation, lower hook site. A, Preparation; B and C, insertion.

FIGURE 149-3 Distraction rod insertion.

Segmental Fixation

Segmental fixation of the Harrington system has been shown to increase stability.^5,⁶ Segmental fixation can be achieved with either sublaminar wires or cables or interspinous techniques.^5,⁹ When sublaminar fixation is chosen as a means of segmental fixation, use of the cables should be considered because they are stronger and more flexible, and the incidence of neurologic complications may be decreased. Placement of a sublaminar wire or cable can be accomplished by removing the interspinous ligament and performing an interlaminar laminotomy along the midline at each level that is to be instrumented. The ligamentum flavum is removed with a Kerrison rongeur, and the dura mater or epidural fat is visualized. Adequate removal of the ligamentum flavum ensures easy passage of the sublaminar wire or cable.

A 16-gauge or 18-gauge wire is doubled and formed into an S or a fishhook shape. Alternatively, a cable leader is bent into an S or fishhook shape. The leader or wire is passed beneath the caudal edge of the lamina gently, without any downward pressure to avoid injury to underlying neural elements. When the tip of the wire or leader is visualized, it is grasped with a clamp, and constant upward pressure is maintained on the wire or cable to minimize canal compromise. When the wire is passed, it is bent over the lamina to guard against inadvertently displacing the wire into the spinal canal. The cable leaders are cut at this point to create two single cables. Sublaminar wires or cables can be placed at each level to be stabilized.

Interspinous Segmental Instrumentation

Interspinous segmental instrumentation can also be used to supplement the strength of the construct.³ A single hole is made at the base of each spinous process to be instrumented, with a curved awl, a bone tenaculum, or a drill. Beaded Wisconsin wires, with attached Drummond buttons, are passed through the base of the spinous process from each side. Once it is through the base of the spinous process, the beaded Wisconsin wire is passed through the contralateral Drummond button. The Wisconsin wires are pulled tight until the Drummond bottom fits snugly against the base of the spinous process. The beads are then cut. When the rods are in place, the wires are tightly secured to the rods, and the excess wire is removed. The free wire ends are bent to provide a low profile (Fig. 149-4).