Although the number of spinal instrumentation systems is overwhelming, the basic concepts are simple. A rigid plate or rod is connected to the spine to limit motion between vertebral segments and allow healing or fusion to occur. There are three ways of connecting the rod or plate to the vertebrae: with a hook, a wire, or a screw. When reduced to these terms, the instrumentation is much simpler.
Most advances in spinal instrumentation arose from the treatment of childhood scoliosis. The first was the Harrington rod-hook system ( Fig 272-14), introduced in
1960 and still in use today. Two major lessons were learned in the development of this system: (1) extremely durable materials were needed to avoid breakage; and
(2) no matter how rigid the instrumentation, failure was inevitable if fusion did not occur ( Fig 272:15). Over the years, many instrumentation systems have been developed with special hook designs that allow the basic Harrington rod concept to be used for a multitude of spinal problems.
FIG. 272-14. This patient's posterior spine fusion was stabilized by a Harrington rod on the left and a Luque rod on the right.
In the 1970s, Eduardo Luque developed a system in which smooth metal rods were laid along the spine and wired to each segment. This created an extremely rigid construct that did not require postoperative bracing. This system is still in use today with only slight modifications ( Fig 272-14). Current systems may use combinations of hooks, screws, and wire for improved fixation and correction of deformity.
The drawback of rod-hook and rod-wire systems is the need for the implant to immobilize over a large number of vertebral levels. This problem has been addressed by pedicle screws placed directly into the vertebral body. This technique dates back to 1949. Because the screw passes through both the posterior and anterior spinal elements, excellent fixation is obtained (Fig 2.7.2.-1.6). This allows the surgeon to greatly reduce the number of segments immobilized. The pedicle screws are then connected to a rigid rod or plate.
Posterior spinal instruments are more commonly used than anterior instrumentation, due in part to the ease and safety of the posterior approach. Numerous types of anterior instrumentation have been developed (Fig 272-17) using same principal of connecting to the vertebrae with a screw that in turn connects to a bridging plate, rod, or cable system.
COMPLICATIONS Early emergency visits usually involve wound problems. Diagnosis of an infection is supported by the presence of severe pain and an elevated temperature, white blood cell count, and erythrocyte sedimentation rate. Painful acute implant failure is not common, but Harrington-type hook implants may disengage. The patient usually notes an acute "pop" and an immediate increase in pain. This is usually best demonstrated on the lateral radiograph because the hook will no longer be under the vertebral lamina ( Fig. 272z18). Rod breakage is usually a late occurrence due to failure of the fusion to prevent motion. Patients greater than 3 months postoperative usually will not have instability. Rod breakage should be easily detectable on standard anteroposterior and lateral radiograph views. Pain complaints from spine surgery patients are commonly encountered in the emergency department. Narcotics should be given sparingly, and communication with the orthopedic surgeon is often helpful in the management of patients with chronic pain.
FIG. 272-18. A. This hook-and-rod system was used to stabilize a lumbar burst fracture. B. The patient noted a "pop" with forward bending, and the lateral radiograph confirms that the top hook was disengaged.
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