Instrumented posterior lumbar interbody fusion in adult spondylolisthesis

Abstract

It is unclear whether using artificial cages increases fusion rates compared with use of bone chips alone in posterior lumbar interbody fusion for patients with lumbar spondylolisthesis. We hypothesized artificial cages for posterior lumbar interbody fusion would provide better clinical and radiographic outcomes than bone chips alone. We assumed solid fusion would provide good clinical outcomes. We clinically and radiographically followed 34 patients with spondylolisthesis having posterior lumbar interbody fusion with mixed autogenous and allogeneic bone chips alone and 42 patients having posterior lumbar interbody fusion with implantation of artificial cages packed with morselized bone graft. Patients with the artificial cage had better functional improvement in the Oswestry disability index than those with bone chips alone, whereas pain score, patient satisfaction, and fusion rate were similar in the two groups. Postoperative disc height ratio, slip ratio, and segmental lordosis all decreased at final followup in the patients with bone chips alone but remained unchanged in the artificial cage group. The functional outcome correlated with radiographic fusion status. We conclude artificial cages provide better functional outcomes and radiographic improvement than bone chips alone in posterior lumbar interbody fusion for lumbar spondylolisthesis, although both techniques achieved comparable fusion rates.

Level of evidence: Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Fig. 1

A photograph shows allogeneic bone chips harvested from the cancellous part of the allograft in the bone bank. They were shaped manually into a rectangle and were approximately 3 × 2 × 5 mm each.

Fig. 2

Radiographic measurement of posterior disc height (PDH), anterolisthesis (ANT), and segmental lordosis is illustrated. Posterior disc height was measured at the maximal point along the posterior disc space. Anterolisthesis was measured from the posterior border of the slipped vertebral body to that of the caudal segment. Both values are expressed as a percentage of the superior end-plate diameter (SED) to normalize the variations between patients. Subsequently, two parameters were obtained: disc height ratio = (PDH/SED)% and slip ratio = (ANT/SED)%. Segmental lordosis was measured from the angle between the upper and lower end plates at the spondylolisthetic level.

Fig. 3A–C

Radiographic assessment of the fusion status after PLIF using (A) bone chips only, (B) a titanium cage, and (C) a PEEK cage is illustrated. The PLIF site was considered fused if there was bridging bone formation over the involved disc space and no radiolucency around the implants (titanium or PEEK cage) on plain radiographs. White marks (arrows) denote the anterior and posterior borders of the radiolucent PEEK cages.

Fig. 4A–C

Lateral radiographs of a 38-year-old woman show Grade 2, L5/S1 isthmic spondylolisthesis (A) before and (B) after treatment with instrumented PLIF with a bone chip graft. (C) Bilateral sacrum screw breakage (arrow) was observed at 10 months. She was pain-free and felt little discomfort from soft tissue irritation over the buttocks at 2 years’ followup.