Influence of the posterior lumbar interbody fusion on the sagittal spino-pelvic parameters in isthmic L5-S1 spondylolisthesis.

Study Design: Prospective study of the sagittal spino-pelvic parameters and deformity parameters in low-grade isthmic spondylolisthesis preoperation and postoperation.

Objective: To better understand how the surgery influences sagittal spino-pelvic alignment in low-grade spondylolisthesis.

Summary Of Background Data: Over the past decade, the importance of the sagittal spino-pelvic parameters was recognized. However, the postoperative change of sagittal balance parameters in low-grade spondylolisthesis was still unclear.

Methods: Forty-nine patients (mean age, 53.2±7.2 y) with low-grade L5-S1 isthmic spondylolisthesis and 60 normal volunteers (mean age, 44.5±8.4 y) were included in the study. Each subject had a radiograph that allowed measurement of sagittal spino-pelvic parameters before and after surgery. The follow-up duration was at least 2 years. Sagittal spino-pelvic parameters and deformity parameters were measured for comparison.

Results: Pelvic incidence, pelvic tilt (PT), sacral slope, lumbar lordosis (LL), lumbar 5 incidence, and lumbosacral angle of normal volunteers were smaller than those of spondylolisthesis patients. All of the parameters changed significantly after the posterior lumbar interbody fusion. Postoperative PT reduced by 4.9 degrees, which had no significant difference compared with the control group (P=0.601). The changes of slip degree and height of the intervertebral disk revealed correlation with the increase of LL (r=-0.483, P=0.003; r=0.365, P=0.010).

Conclusion: The improvement of PT may play an important role in the reconstruction of the sagittal alignment and therapeutic outcome. The restoration of the slip degree and height of the intervertebral disk would increase the LL with a wedged cage. To get a better LL, the size and geometry of the cage was recommended to be evaluated before surgical treatment.