What Surgical Treatment Is Best for Isthmic Spondylolisthesis?: Commentary on an article by Peter Endler, MD, et al.

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Surgical fusion is an accepted form of treatment, supported by evidence-based medicine, for symptomatic isthmic spondylolisthesis in patients for whom appropriate nonoperative care has not provided satisfactory outcomes1. Endler et al. provided support for this treatment recommendation by identifying a significant and lasting quality-of-life improvement in a study of 765 patients enrolled from 1999 through 2008 and followed for at least 2 years, with 586 followed for longer (an average of 6.9 years). The main focus of this study, however, was to provide the largest-to-date comparison of the efficiency of 3 arthrodesis techniques for treating isthmic spondylolisthesis: (1) a traditional in situ fusion technique with autologous in situ bone graft, (2) a pedicle-screw-augmented procedure with a mixture of local and iliac crest graft, and (3) a circumferential fusion including an interbody device together with posterior instrumentation. In keeping with a recent systematic review and a prospective randomized trial1-3, the authors found some differences among procedures with respect to certain typical patient-reported outcomes measures up to 2 years following surgery; however, these differences disappeared at 5 to 10 years. In contrast, the reoperation rate was about 3 to 4 times higher ≥10 years following fusion with an interbody device than it was ≥10 years following fusion without instrumentation. On the basis of these findings, the authors called into question the merits of using an interbody device and posterior pedicle screw fixation, which is both a more extensive and a more expensive (because of higher implant cost) form of surgical treatment for isthmic spondylolisthesis.
There are methodology-related questions about this study because of the inherent limitations of registry-based investigations. The data for this study were derived from the oldest comprehensive continuous regional (and in this case national) database on spine surgery of its kind, the Swedish Spine Register (Swespine). This prospective data-gathering tool was organized by the Swedish Society of Spinal Surgeons, which has operated the registry since its inception in 19934. The data entry for baseline demographic and patient-reported outcomes measures is performed by surgeons and their staff at the 42 to 45 registered spine surgery departments in the participating 35 to 39 hospitals. The Swespine organization then independently obtains all additional patient-reported outcomes measures as well as reoperation data and attempts to receive follow-up data at set 1, 2, 5, and 10-year intervals and beyond directly from the patients to ensure data integrity. Their published facility compliance and follow-up rates range from approximately 70% to 80%, which is in keeping with more recently introduced registries5-8. To provide the highest possible assurance of data integrity in this study, the authors actually went back to the clinical source records and could validate correct registry information for 97% of the patients. Also, in anticipation of the possibility of reporting bias due to asymmetric patient follow-up, which is a justified concern, the authors performed a formal comparison of patients who did and those who did not respond to follow-up inquiries by the study organization. They found no substantial differences in demographic data or patient-reported outcomes. In contrast to other studies, this study demonstrated no differences in surgical complications between the fusions done without instrumentation and the 2 surgical instrumentation groups.
Radiographic variables that may influence surgical decision-making are outside the scope of this study. The type of isthmic spondylolisthesis, its severity, instability on dynamic studies, disc height, sacral slope, sagittal alignment, bone quality, and the need for lateral neural element decompression all, or individually, may determine the need for a more definitive surgical stabilization procedure with instrumentation.
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