Interbody Fusion Cages in Reconstructive Operations on the Spine*

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During the last five years, surgeons around the world have inserted more than 80,000 lumbar interbody fusion cages; in the United States alone, an estimated 5000 such devices are implanted each month. The recent interest in performing lumbar interbody arthrodesis with use of cages is attributable to three factors: the high rate of failure associated with use of bone graft alone [3,22,26,45,46,71,82,84,94,96,106,107]; the high rate of failure associated with use of posterior pedicle-screw instrumentation [39,97,102]; and the high rate of success associated with use of so-called stand-alone anterior fusion cages and autogenous bone graft, obviating the need to perform a 360-degree (combined anterior and posterior) lumbar arthrodesis with use of posterior instrumentation [77].The purpose of the current review is to summarize the information in the literature with regard to the background, rationale, indications, techniques, results, and possible future developments of interbody arthrodesis for reconstruction of the spine.BackgroundEarly techniques of arthrodesis with use of allograft or autogenous graft and without instrumentation were associated with a high rate of failure. In a classic study, Stauffer and Coventry [96] reported on eighty-three patients who had had an anterior interbody arthrodesis between 1959 and 1967. Of seventy-seven patients who were followed clinically for an average of 3.75 years after the procedure, twenty-eight (36 percent) had good (76 to 100 percent) relief of pain, fifteen (19 percent) had fair (26 to 75 percent) relief, and thirty-four (44 percent) had poor (0 to 25 percent) relief. Thirty (44 percent) of sixty-eight patients who were evaluated radiographically at a minimum of eighteen months postoperatively had a pseudarthrosis. Stauffer and Coventry defined radiographic fusion as "a pattern of continuous trabeculae traversing the grafted region and the adjacent vertebral bodies, with no evidence of motion when the patient was bending." These results, and the equally unfavorable results reported by other investigators [20,26,33,45,56,57,82], prompted investigation into and development of various augmentation devices to improve the long-term outcome of spinal arthrodesis.Technology of Interbody Fusion CagesHistoryBagby [2] was responsible for the early development of the lumbar interbody fusion cage. Working with a veterinarian, Grant, and a series of thoroughbred horses that had wobbler syndrome (a form of spondylitic myelopathy that leads to ataxia), he found that the Cloward technique [20], which requires obtaining bone from the iliac crest, resulted in unacceptable morbidity. Bagby then developed a novel device, the first interbody stainless-steel basket (the Bagby basket), which was a thirty-millimeter-long, twenty-five-millimeter-diameter cylinder that had two-millimeter fenestrations in its walls to allow bone ingrowth. During a standard anterior cervical decompression and reaming procedure, cancellous-bone chips were removed from the posterior aspects of the cervical vertebrae. These chips then were packed inside the basket to promote anterior interbody cervical fusion.Subsequent studies revealed that horses treated with the Bagby technique had improved neurological function; some not only survived for many years but also won races [38]. Other investigators began making modifications of this technique, including threads in the basket [72,108], adaptation of the cage for use in posterior lumbar interbody arthrodesis, and increases in the pullout and compressive strength [72]; a two-cage technique also was developed, in 1988 [25]. In another study of horses, DeBowes et al. [30] compared the results of arthrodesis with use of bovine xenograft with those of arthrodesis with use of autogenous graft inside a Bagby basket; they found that the rate of fusion was better when the Bagby basket had been used and that this device did not collapse.

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