Unintended facet fusions after Dynesys dynamic stabilization in patients with spondylolisthesis

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The pedicle screw–based Dynesys dynamic stabilization (DDS) has reportedly become a surgical option for lumbar spondylosis and spondylolisthesis. However, it is still unclear whether the dynamic construct remains mobile or eventually fuses. The aim of this study was to investigate the incidence of unintended facet arthrodesis after DDS and its association with spondylolisthesis.


This retrospective study was designed to review 105 consecutive patients with 1- or 2-level lumbar spondylosis who were treated with DDS surgery. The patients were then divided into 2 groups according to preexisting spondylolisthesis or not. All patients underwent laminectomies, foraminotomies, and DDS. The clinical outcomes were measured using visual analog scale (VAS) scores for back and leg pain, Japanese Orthopaedic Association (JOA) scores, and Oswestry Disability Index (ODI) scores. All medical records, including pre- and postoperative radiographs, CT scans, and MR images, were also reviewed and compared.


A total of 96 patients who completed the postoperative follow-up for more than 30 months were analyzed. The mean age was 64.1 ± 12.9 years, and the mean follow-up duration was 46.3 ± 12.0 months. There were 45 patients in the spondylolisthesis group and 51 patients in the nonspondylolisthesis group. The overall prevalence rate of unintended facet fusion was 52.1% in the series of DDS. Patients with spondylolisthesis were older (67.8 vs 60.8 years, p = 0.007) and had a higher incidence rate of facet arthrodesis (75.6% vs 31.4%, p < 0.001) than patients without spondylolisthesis. Patients who had spondylolisthesis or were older than 65 years were more likely to have facet arthrodesis (OR 6.76 and 4.82, respectively). There were no significant differences in clinical outcomes, including VAS back and leg pain, ODI, and JOA scores between the 2 groups. Furthermore, regardless of whether or not unintended facet arthrodesis occurred, all patients experienced significant improvement (all p < 0.05) in the clinical evaluations.


During the mean follow-up of almost 4 years, the prevalence of unintended facet arthrodesis was 52.1% in patients who underwent DDS. Although the clinical outcomes were not affected, elderly patients with spondylolisthesis might have a greater chance of facet fusion. This could be a cause of the limited range of motion at the index levels long after DDS.

ABBREVIATIONS DDD = degenerative disc disease; DDS = Dynesys dynamic stabilization; JOA = Japanese Orthopaedic Association; ODI = Oswestry Disability Index; ROM = range of motion; VAS = visual analog scale.

Article Information

Correspondence Jau-Ching Wu: Neurological Institute, Taipei Veterans General Hospital, Taipei, Taiwan. jauching@gmail.com.

INCLUDE WHEN CITING Published online December 7, 2018; DOI: 10.3171/2018.8.SPINE171328.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.



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    Pie charts demonstrating the distribution of the index levels that were treated using DDS.

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    Serial images obtained in a 68-year-old man who required lumbar spine surgery. A: Preoperative sagittal MR image. There was spinal stenosis at L3–5. B: Preoperative CT sagittal view of the left facet joints (arrowheads). C and D: Preoperative axial CT scan of L3–4 and L4–5. The joint spaces are visible (arrowheads). E: Postoperative lateral radiograph. F: Postoperative sagittal CT scan of the left facet joints (arrowheads). G and H: Postoperative axial CT of L3–4 and L4–5. The joint spaces are visible (arrowheads).

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    Serial images obtained in a 59-year-old woman who needed lumbar spine surgery. A: Preoperative sagittal MR image. Spinal stenosis and spondylolisthesis are seen at L4–5. B: Preoperative sagittal CT scan of the left facet joints (arrowhead). C and D: Preoperative axial CT scans of different slices of L4–5. The joint spaces (arrowheads) were not changed. E: Postoperative lateral plain radiograph. F–H: Postoperative sagittal CT scan of the left facet joints (F) and postoperative axial CT scans of different cuts of L4–5 (G and H). The joint spaces were fused (arrow).

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    Bar graphs showing the JOA scores (A), ODI scores (B), and the VAS scores for back pain (C) and leg pain (D) at each time point of observation. There were significant improvements postoperatively when compared with that assessed preoperatively (p < 0.05 at each time point). The numbers indicate the mean value of each score.



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