Early postoperative sacral fracture after short-segment posterior lumbar interbody fusion for L5/S1 isthmic spondylolisthesis: A case report

INTRODUCTION

Early postoperative sacral fractures following L5/S1 posterior lumbar interbody fusion (PLIF) are rare. Here, a 71-year-old female sustained a postoperative sacral fracture after a L5/S1 PLIF performed for isthmic spondylolisthesis. Following a secondary fusion to the pelvis utilizing bilateral iliac screws, the patient’s complaints resolved.

CASE DESCRIPTION

Clinical presentation and first surgery

A 71-year-old female with low back pain and right lower extremity sciatica had initial MR and CT studies that revealed L5/S1 isthmic spondylolisthesis (near Grade 3) and a Cobb’s angle of 19.3° [Figure 1a-d]. The L5/S1 PLIF was performed using pedicle screws (7.5 mm × 50 mm and 7.5 × 45 mm) and an interbody cage. One day postoperative lumbar X-rays/CT studies, and the MRI obtained at 1 postoperative week, documented resolution of the L5/S1 isthmic spondylolisthesis [Figure 2a and b].

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Figure 1:: Anteroposterior (a) and lateral (b) radiographs of the lumbar spine before lumbosacral fusion demonstrated isthmic spondylolisthesis at L5/S1 with mild scoliosis. T1- (c) and T2-weighted images (d) showed isthmic spondylolisthesis of L5 on S1.

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Figure 2:: Anteroposterior (a) and lateral (b) radiographs of the lumbar spine after lumbosacral fusion showed improvement of the L5/ S1 spondylolisthesis. T1- (c) and T2-weighted images (d) indicated the sacral fracture (white arrows) 3 weeks after the lumbosacral fusion.

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Second surgery

Two weeks later, the right leg numbness recurred. By the ^3rd postoperative week, X-rays and MRI studies showed a sacral insufficiency fracture, with instability above the sacral fracture, and anterolisthesis of S1 [Figure 2c and d, Figure 3]. The posterior fusion was then extended to the pelvis using bilateral iliac screws (8.5 mm × 70 mm and 7.5 mm × 50 mm). One month postoperatively, X-rays, CT, and MRI examinations confirmed fusion, and the patient was now asymptomatic [Figure 4, Tables 1, 2].

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Figure 3:: Lateral radiographs of the lumbar spine in the sitting (a) and supine positions (b) after lumbosacral fusion showing instability at the S1/S2 level.

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Figure 4:: Postoperative anteroposterior (a) and lateral (b) radiographs of the lumbar spine following the lumbopelvic fusion.

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Table 1:: Summary of the pelvic parameters.

Table 2:: Summary of the VAS score and the ODI score.

DISCUSSION

Sacral insufficiency fractures are typically complications of previous long-segment instrumented lumbosacral fusions, but rarely involve single-level PLIF [Table 3].[1,3,5-8] According to Klineberg et al. and Odate et al., the incidence of sacral insufficiency fractures is 3.1–4.3% for long-segment versus just 1.3% for short-segment instrumented lumbosacral fusions.[2,4] Before performing short-segmental lumbosacral fusions, bone density studies should be performed to rule out osteoporosis, especially in elderly females with high-grade L5/S1spondylolisthesis. Certainly, patients showing radiographic confirmation of instability/fractures at the postoperative surgical site on X-ray/MR/CT studies and should be considered for placement of bilateral lumbosacral iliac screws.

Table 3:: The risk factors of sacral fractures after lumbosacral fusion.

CONCLUSION

A 71-year-old female developed an early postoperative sacral fracture after a L5/S1 PLIF for isthmic spondylolisthesis. Following extension of the fusion to the pelvis using bilateral iliac screws, the patient became asymptomatic and achieved successful arthrodesis.