Evidence & Methods
In low-grade isthmic spondylolithesis, debate persists regarding the optimal type of surgical intervention and specifically whether interbody fusion is necessary (in light of its ability to restore spino-pelvic parameters to a greater extent). The authors report the results of a small series of patients treated using interbody or porterolateral fusion and followed prospectively.
The authors report that among their 99 patients (63 PLIF and 36 PLF), lumbar lordosis and sagittal alignment were restored to a greater extent following interbody fusion. The fusion rate was also higher among those who underwent PLIF. At two-year follow-up, however, no significant difference was appreciated in clinical outcome between the two groups.
This study reinforces findings documented in other studies, particularly an increased capacity on the part of interbody techniques to restore spino-pelvic parameters and an increased rate of radiographic fusion among patients receiving PLIF. At the same time, clinical outcomes were comparable between the two groups over the course of this study. This finding may call into question the rationale behind a procedure (interbody fusion) that is both more expensive and carries a greater risk of complications. Readers should appreciate that, even though this investigation was conducted prospectively, the small sample size and potential for selection bias in assigning patients to the treatment groups results in this work presenting no better than Level III evidence.
—The Editors
With the development of pedicle screw–based instrumentation, spine surgery has had great progress. But some orthopedic surgeons did not focus attention on the sagittal balance of the spine. Many patients suffered from low back pain that resulted from the fixed sagittal imbalance. Some of them had to maintain a forward bending position.
The concept of spine sagittal balance has been studied since 1985 [1]. Duval- Beaupère et al. [2] first described the pelvic incidence (PI) in 1992, which was the most widely used sagittal spinopelvic parameter. The excellent intraobserver reliability and interobserver reliability for the measurement of the PI was proved by Boulay et al. [3]; they compared the PI measured separately from the X-ray films and anatomical specimens. The PI was a morphologic parameter to characterize the sacropelvis, which would not be affected by the position of the individual. It was defined as the angle subtended by a line perpendicular to the upper sacral plate at its midpoint and the line connecting this midpoint to the middle axis of the femoral heads. PI also represented a special geometric relationship with pelvic tilt (PT) and sacral slope (SS), which was the arithmetic sum of the PT and SS. PI was strongly correlated to the SS (r=0.80) and lumbar lordosis (LL) (r=0.60) [4], [5].
Isthmic spondylolisthesis is the forward slippage of a vertebra on the caudad vertebra resulting from a defect in the pars interarticularis, which was most common at the L5–S1 segment. PI was significantly higher in patients with spondylolisthesis. Many studies had confirmed the relationship between PI and the severity of spondylolisthesis [6], [7], [8]. Although the etiology of isthmic spondylolisthesis was still uncertain, the abnormal spinopelvic anatomy could be an important factor.
The relationship between the surgical outcome and the sagittal alignment of the sacropelvis has been researched since the development of the PI system. Recently, high-grade spondylolisthesis had been divided into balanced and unbalanced type with the spinopelvic parameters [9]. Surgical treatment can improve the sagittal spinopelvic balance of the unbalanced patients [10]. With great effort, the Spinal Deformity Study Group proposed a new classification of the lumbosacral spondylolisthesis. They divided the L5–S1 spondylolisthesis into six subtypes according to the slip grade, PI, and sagittal balance [11], [12].
The PLIF and PLF were two typical operations for isthmic spondylolisthesis. Much effort was made to prove the better operation. Theoretically, the advantage of the PLIF included anterior column support, indirect foraminal decompression, restoration of lordosis, removal of the pain-generating degenerated disc, and reduction of the slip via ligamentotaxis [13]. But PLIF and PLF did not affect the short-period outcome of surgical treatment of adult isthmic spondylolisthesis [14], [15], [16]. The need of the interbody fusion for isthmic spondylolisthesis was in dispute.
Our study had proved that the PLIF could improve sagittal spinopelvic balance [17]. As the PLF once was a gold standard operation for the isthmic spondylolisthesis, we had been wondering about the postoperative change of the sagittal spinopelvic parameters after the PLF operation.
The objective of this study was to describe the change of the spinopelvic parameters after the operation and compare the influence on the sagittal alignment of the PLF with the PLIF. With the result of our study, we hope we can find a better way to reconstruct the sagittal alignment of the spinopelvic region.