Letter to the Editor: Pedicle screw–based dynamic stabilization and adjacent-segment disease

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TO THE EDITOR: We read with great interest the article by Dr. Han and colleagues4 (Han Y, Sun J, Luo C, et al: Comparison of pedicle screw–based dynamic stabilization and fusion surgery in the treatment of radiographic adjacent-segment degeneration: a retrospective analysis of single L5–S1 degenerative spondylosis covering 4 years. J Neurosurg Spine 25:706–712, December 2016). The authors conducted a head-to-head comparison of 31 cases in which patients underwent pedicle screw–based dynamic stabilization (PDS) with 31 cases in which patients underwent standard posterior lumbar interbody fusion (PLIF) for L5–S1 spondylosis. They concluded that the incidence of

TO THE EDITOR: We read with great interest the article by Dr. Han and colleagues4 (Han Y, Sun J, Luo C, et al: Comparison of pedicle screw–based dynamic stabilization and fusion surgery in the treatment of radiographic adjacent-segment degeneration: a retrospective analysis of single L5–S1 degenerative spondylosis covering 4 years. J Neurosurg Spine 25:706–712, December 2016). The authors conducted a head-to-head comparison of 31 cases in which patients underwent pedicle screw–based dynamic stabilization (PDS) with 31 cases in which patients underwent standard posterior lumbar interbody fusion (PLIF) for L5–S1 spondylosis. They concluded that the incidence of adjacent-segment disease (ASD) 4 years after surgery was similar in patients treated with PDS and those treated with PLIF. Also, the authors found pre-existing disc degeneration at L4–5 to be an independent risk factor for ASD detected radiographically later on. Thus, the authors made the statement that PDS is feasible for L5–S1 spondylosis and pre-existing ASD does not necessitate any additional treatment, only observation, in the absence of clinical symptoms or signs.

We would like to respectfully point out 2 caveats pertaining to this study. First, the necessity of instrumentation for L5–S1 spondylosis is controversial, particularly given that the authors mentioned in their Methods that there was no instability. Unlike percutaneous screws, a conventional open approach for the placement of pedicle screws at L-5 inevitably involves dissection of the facet capsule and surrounding musculature of L4–5, which could predispose patients to acceleration of pre-existing ASD. Second, the authors used a midline approach rather than the Wiltse approach, which is usually recommended for candidates for PDS. Patients who have undergone surgery using the Wiltse approach reportedly have decreased risks of wound infection, reoperation, and ASD.8

The rationale for the use of PDS systems is preservation of segmental motion and protection from disc degeneration at both the indexed and adjacent segments.2,7,9 For an optimal chance of reducing ASD, the pedicle screws are thus suggested to be inserted via the Wiltse approach without any facet violation.5 In the literature, the main concerns related to PDS were screw loosening and facet arthrodesis.1,5,6,10 Although most reports demonstrated satisfactory clinical outcomes with PDS, whether it protects against ASD remains debatable.1,3,10 Further investigations—particularly investigations involving larger numbers of patients—are required to clarify the risk factors of ASD, as well as the best candidates for PDS systems. Nevertheless, the authors are commended for sharing their experience with worldwide readers of the Journal of Neurosurgery: Spine. Their study demonstrates promising results for the application of dynamic stabilization.

Disclosures

The authors report no conflict of interest.

References

  • 1

    Fay LYChang PYWu JCHuang WCWang CHTsai TY: Dynesys dynamic stabilization–related facet arthrodesis. Neurosurg Focus 40:1E42016

  • 2

    Fay LYWu JCTsai TYTu THWu CLHuang WC: Intervertebral disc rehydration after lumbar dynamic stabilization: magnetic resonance image evaluation with a mean followup of four years. Adv Orthop 2013:4375702013

  • 3

    Fay LYWu JCTsai TYWu CLHuang WCCheng H: Dynamic stabilization for degenerative spondylolisthesis: evaluation of radiographic and clinical outcomes. Clin Neurol Neurosurg 115:5355412013

  • 4

    Han YSun JLuo CHuang SLi LJi X: Comparison of pedicle screw–based dynamic stabilization and fusion surgery in the treatment of radiographic adjacent-segment degeneration: a retrospective analysis of single L5–S1 degenerative spondylosis covering 4 years. J Neurosurg Spine 25:7067122016

  • 5

    Ko CCTsai HWHuang WCWu JCChen YCShih YH: Screw loosening in the Dynesys stabilization system: radiographic evidence and effect on outcomes. Neurosurg Focus 28:6E102010

  • 6

    Kuo CHChang PYTu THFay LYChang HKWu JC: The effect of lumbar lordosis on screw loosening in dynesys dynamic stabilization: four-year follow-up with computed tomography. Biomed Res Int 2015:1524352015

  • 7

    Kuo CHChang PYWu JCChang HKFay LYTu TH: Dynamic stabilization for L4-5 spondylolisthesis: comparison with minimally invasive transforaminal lumbar interbody fusion with more than 2 years of follow-up. Neurosurg Focus 40:1E32016

  • 8

    Street JTAndrew Glennie RDea NDiPaola CWang ZBoyd M: A comparison of the Wiltse versus midline approaches in degenerative conditions of the lumbar spine. J Neurosurg Spine 25:3323382016

  • 9

    Wu JCHsieh PCMummaneni PVWang MY: Spinal motion preservation surgery. Biomed Res Int 2015:3725022015

  • 10

    Wu JCHuang WCTsai HWKo CCWu CLTu TH: Pedicle screw loosening in dynamic stabilization: incidence, risk, and outcome in 126 patients. Neurosurg Focus 31:4E92011

Response

We are pleased to respond to the letter from Professor Cheng and colleagues.

There were 2 reasons why we did not include simple decompression in our study. The first reason was that a complete decompression would have required en bloc laminectomy, which can jeopardize lumbar spine stability, and spinal instability is one of the risk factors for lower back pain and segmental degeneration. The other reason was that the limited access and visualization of simple decompression may lead to nerve injury and incomplete decompression. Nerve injury may be related to inadequate intracanal exposure or excessive nerve retraction, which can be minimized by wide decompressive laminectomies. Furthermore, patients may experience recurrence of signs and symptoms of disc herniation or canal stenosis due to incomplete decompression. For these reasons, we adopted PLIF or PDS to treat the 62 patients who met the inclusion criteria. Definitely, simple decompression and discectomy were used in some cases that were excluded from this study.

The Wiltse approach exploits the avascular intermuscular plane between the multifidus and longissimus, leading to better tissue conservation, less pressure during retraction, and less bleeding. We did use the Wiltse approach in several cases, but the number was too small to allow for inclusion of those cases in our study.

Thank you for your interest in our paper.

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Article Information

INCLUDE WHEN CITING Published online November 11, 2016; DOI: 10.3171/2016.7.SPINE16816.

© AANS, except where prohibited by US copyright law.

Headings

References

1

Fay LYChang PYWu JCHuang WCWang CHTsai TY: Dynesys dynamic stabilization–related facet arthrodesis. Neurosurg Focus 40:1E42016

2

Fay LYWu JCTsai TYTu THWu CLHuang WC: Intervertebral disc rehydration after lumbar dynamic stabilization: magnetic resonance image evaluation with a mean followup of four years. Adv Orthop 2013:4375702013

3

Fay LYWu JCTsai TYWu CLHuang WCCheng H: Dynamic stabilization for degenerative spondylolisthesis: evaluation of radiographic and clinical outcomes. Clin Neurol Neurosurg 115:5355412013

4

Han YSun JLuo CHuang SLi LJi X: Comparison of pedicle screw–based dynamic stabilization and fusion surgery in the treatment of radiographic adjacent-segment degeneration: a retrospective analysis of single L5–S1 degenerative spondylosis covering 4 years. J Neurosurg Spine 25:7067122016

5

Ko CCTsai HWHuang WCWu JCChen YCShih YH: Screw loosening in the Dynesys stabilization system: radiographic evidence and effect on outcomes. Neurosurg Focus 28:6E102010

6

Kuo CHChang PYTu THFay LYChang HKWu JC: The effect of lumbar lordosis on screw loosening in dynesys dynamic stabilization: four-year follow-up with computed tomography. Biomed Res Int 2015:1524352015

7

Kuo CHChang PYWu JCChang HKFay LYTu TH: Dynamic stabilization for L4-5 spondylolisthesis: comparison with minimally invasive transforaminal lumbar interbody fusion with more than 2 years of follow-up. Neurosurg Focus 40:1E32016

8

Street JTAndrew Glennie RDea NDiPaola CWang ZBoyd M: A comparison of the Wiltse versus midline approaches in degenerative conditions of the lumbar spine. J Neurosurg Spine 25:3323382016

9

Wu JCHsieh PCMummaneni PVWang MY: Spinal motion preservation surgery. Biomed Res Int 2015:3725022015

10

Wu JCHuang WCTsai HWKo CCWu CLTu TH: Pedicle screw loosening in dynamic stabilization: incidence, risk, and outcome in 126 patients. Neurosurg Focus 31:4E92011

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