High-Grade Adult Isthmic L5–S1 Spondylolisthesis: A Report of Intraoperative Slip Progression Treated with Surgical Reduction and Posterior Instrumented Fusion

摘要

Adult isthmic spondylolisthesis most commonly occurs at the L5–S1 level of the lumbar spine. Slip progression is relatively rare in adults with this condition and slippage is typically associated with advanced degeneration of the disk below the pars defect. When symptomatic, radiculopathy is the typical complaint in adults with isthmic spondylolisthesis. When considering options for surgical treatment of adult isthmic spondylolisthesis, the surgeon must consider several different options, such as decompression, fusion, instrumentation, reduction, and type of bone graft to be used. All of these decisions must be individualized as deemed appropriate for each particular patient. This report presents a case of intraoperative slip progression of a L5–S1 adult isthmic spondylolisthesis to a high-grade slip, which was treated with complete surgical reduction and posterior instrumented fusion. This case demonstrates the potential instability of this condition in adults and has not been previously reported. The case details and images are reviewed and the intraoperative decisions, treatment options, and patient outcome are discussed. Keywords: adult isthmic spondylolisthesis, high-grade spondylolisthesis, slip progression, surgical reduction, posterior instrumented fusion Adult isthmic spondylolisthesis most commonly occurs at the L5–S1 level of the lumbar spine. Its incidence has been reported to be 4% by the age of 6 years and 6% by adulthood. 1 Multiple classification systems have been established to help describe the amount of slippage present and attempt to determine etiology. It is generally accepted that isthmic spondylolisthesis is caused by insult to the pars interarticularis, whether it is due to stress or fatigue fractures, progressive elongation without separation, lytic destruction, or congenital defects. 2 3 4 5 One of the most common classification systems used to quantify the slip is that described by Meyerding. 2 According to this system, grade I defines a slip from 0 to 25%, grade II from 26 to 50%, grade III from 51 to 75%, and grade IV from 76 to 100%. Regardless of the classification system used, a high-grade slip is generally considered to be one in which the cephalad vertebra has translated greater than 50% the width of the caudad vertebra (greater than grade II). Although progression of isthmic spondylolisthesis has been documented in adolescents, its occurrence in adults is unknown. One study 6 examined 21 adults with isthmic spondylolisthesis and reported that slip progression ranged from 8 to 30% during a period of 3 to 20 years after the fourth decade of life. The slippage was typically associated with advanced degeneration of the disk below the pars defect. This report presents a case of intraoperative slip progression of an L5–S1 adult isthmic spondylolisthesis to a high-grade slip, which was treated with surgical reduction and posterior instrumented fusion. This case demonstrates the potential instability of this condition in adults and has not been previously reported. The case details and images are reviewed, and the intraoperative decisions, treatment options, and patient outcome are discussed.