IntroductionThe outcome of treatment for idiopathic scoliosis is usually assessed by radiologic study, to determine the angular correction obtained, and by analysis of the clinical results. Another datum of interest, particularly regarding vertebral implants, is the incidence of reoperations. From the patient's viewpoint, an implant that achieves excellent correction but is very likely to require a second operation may not be considered satisfactory. The appropriate statistical method for evaluating this event is survivorship analysis, which allows one to determine the true reoperation rate and to predict the probability of reoperation in the long Abstract This study presents a survivorship analysis of Cotrel-Dubousset instrumentation in the surgical treatment of idiopathic scoliosis. Between 1987 and 1995, a total of 133 patients with idiopathic scoliosis received posterior spine fusion and instrumentation with the CD system at our center. The patients' mean age at surgery was 16.5 years (range 11-43 years). The magnitude of the thoracic scoliosis averaged 62.7°(range 40°-125°) and that of the lumbar curve was 58.8°(range 40°-100°). On average, 12.2 segments were fused (range 8-17) and, excluding the rods, 14.1 implants were set for each patient (range 10-21). Survivorship analysis was carried out using the Kaplan-Meier method. Implant removal was considered the terminal event, or "death". The effect of several variables on survival rate was determined with the Cox regression method. The patients remained in the study for 56.7 months (range 2-120 months). One-hundred and ten patients were withdrawn ("censored"): 90 "alive" (did not require repeat surgery and attended followup control in 1997) and 20 "lost" (did not attend control in 1997). Twenty-three patients attained the terminal event of implant removal for a variety of reasons: acute infection (three cases), late infection (ten cases), implant failure requiring revision (six cases) and local pain (four cases). The survival rate was 95.5% at 3 months, 94.7% at 6 months, 93.9% at 1 year, 91.5% at 2 years, 82.2% at 5 years and 76.5% at 10 years. The magnitude of the curves, total number of implants and number of fused segments did not correlate with survival probability. A positive correlation was found between survival rate and correction loss between surgery and last control. A survival rate of 76.5% at 10 years is unexpectedly low. Current data suggest that the incapacity to maintain correction after initial surgery plays a major roll in the long-term evolution of CotrelDubousset instrumentation.

Isthmic spondylolisthesis must be considered as a cause within VBI. Surgery presents good results.

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