Letter to the Editor. Proximal junctional kyphosis and proximal junctional failure

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  • 1 University of Virginia Health System, Charlottesville, VA; and
  • | 2 Presbyterian St. Luke’s/Rocky Mountain Hospital for Children, Denver, CO
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TO THE EDITOR: We read with great interest the outstanding article by Safaee and colleagues4 (Safaee MM, Deviren V, Dalle Ore C, et al: Ligament augmentation for prevention of proximal junctional kyphosis and proximal junctional failure in adult spinal deformity. J Neurosurg Spine 28:512–519, May 2018). The authors compared outcomes of proximal junctional kyphosis/failure (PJK/PJF) between a historical cohort and a treatment group of adult spinal deformity (ASD) patients receiving ligamentous augmentation at the upper instrumented vertebra (UIV), 1 level above the UIV (UIV+1), and 1 level below the UIV (UIV−1). Ligamentous augmentation was performed by passing 2 sublaminar cables through each of these levels, tightening them to achieve the desired tension, and locking them into place onto bilateral rods. The results suggest that ligamentous augmentation at the junctional levels (the junction of fused and adjacent unfused segments) may indeed be an effective strategy for PJK/PJF prevention in ASD cases.

These results are consistent with our own institution’s retrospective analysis of consecutive ASD operations performed with a similar ligamentous augmentation technique. We previously reported that posteriorly anchored junctional tethers (tethering the proximal terminus of fusion constructs to UIV+1 with polyethylene tape) significantly reduced the occurrence of PJK.2 Despite these positive clinical results, the exact mechanism for how ligamentous augmentation prevents PJK is incompletely understood. Current preliminary evidence from a finite element analysis by Bess et al. suggests that posterior tethers mitigate adjacent-segment stress by attenuating the abrupt biomechanical transition between the rigid instrumented spine and adjacent unfused segments.1

Safaee et al. astutely pointed out that their ligament augmentation cohort contained a greater proportion of patients with UIV hook fixation and vertebroplasty.4 These techniques may also prevent PJK.3,5 The authors controlled for the differences in rates of UIV hook fixation and vertebroplasty with multivariate analysis.

For future studies investigating PJK/PJF prophylaxis, Safaee et al. proposed a more standardized metric by reporting the magnitude of change in the proximal junctional angle (PJA) rather than the binary outcome of PJK. We agree that reporting the change in PJA would be helpful for more reliable analysis across studies, since definitions of PJK are variable. In our prior study, the mean change in PJA was 8° (ligamentous augmentation with tether-crosslink) compared with 13° (historical control).2 Again, our results are consistent with the current study: Safaee et al. reported that the mean change in PJA was 6° (ligamentous augmentation with sublaminar cables) compared with 14° (historical control).

The current investigation and our prior study both report possible benefit from ligamentous augmentation techniques, but they do not offer guidelines for pretensioning. Tension of the ligamentous augmentation technique (tether or sublaminar cable) is left to the discretion of the surgeon. We think that there is likely an optimal range of pretensioning for maximal PJK prevention. In fact, overtightening may actually predispose to PJK at the level above the proximal attachment of the tether or cable. Therefore, if tension meters are utilized and pretensioning is reported in future investigations, this could help create more standardized guidelines for ligamentous augmentation techniques in ASD.

Again, we commend the authors on this excellent study.

Disclosures

Bess: research support from K2M, NuVasive, Medtronic, DePuy Synthes, ZimmerBiomet, Allosource, Orthofix, and EOS; consultant for K2M, Allosource, DePuy Synthes, Misonix, and EOS; and patent holder with K2M and Innovasis. Shaffrey: consultant for Medtronic, NuVasive, Zimmer Biomet, and K2M; and patent holder with and royalties from Medtronic, NuVasive, and Zimmer Biomet; stock holder with NuVasive. Smith: royalties from Zimmer Biomet; consultant for Zimmer Biomet, Cerapedics, NuVasive, K2M, and AlloSource; honoraria from Zimmer Biomet, NuVasive, and K2M; research support from DePuy Synthes and ISSGF; and fellowship support from NREF and AOSpine.

References

  • 1

    Bess S, Harris JE, Turner AW, LaFage V, Smith JS, Shaffrey CI, et al. : The effect of posterior polyester tethers on the biomechanics of proximal junctional kyphosis: a finite element analysis. J Neurosurg Spine 26:125133, 2017

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  • 2

    Buell TJ, Buchholz AL, Quinn JC, Bess S, Line BG, Ames CP, et al. : A pilot study on posterior polyethylene tethers to prevent proximal junctional kyphosis after multilevel spinal instrumentation for adult spinal deformity. Oper Neurosurg (Hagerstown) [epub ahead of print], 2018

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  • 3

    Ghobrial GM, Eichberg DG, Kolcun JPG, Madhavan K, Lebwohl NH, Green BA, et al. : Prophylactic vertebral cement augmentation at the uppermost instrumented vertebra and rostral adjacent vertebra for the prevention of proximal junctional kyphosis and failure following long-segment fusion for adult spinal deformity. Spine J 17:14991505, 2017

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    • Export Citation
  • 4

    Safaee MM, Deviren V, Dalle Ore C, Scheer JK, Lau D, Osorio JA, et al. : Ligament augmentation for prevention of proximal junctional kyphosis and proximal junctional failure in adult spinal deformity. J Neurosurg Spine 28:512519, 2018

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5

    Thawrani DP, Glos DL, Coombs MT, Bylski-Austrow DI, Sturm PF: Transverse process hooks at upper instrumented vertebra provide more gradual motion transition than pedicle screws. Spine (Phila Pa 1976) 39:E826832, 2014

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  • University of California, San Francisco, CA

Response

We appreciate the careful attention to our paper by Buell et al. and are pleased with their results. Of particular interest are the similarities between PJA changes in ligament augmentation groups compared with historical controls across both studies. These data provide preliminary evidence that our reductions in PJK and PJF with ligament augmentation are indeed reproducible. With respect to tensioning of the tether, the force should be adjusted to account for bone quality and robustness of the spinous process fixation points. We prefer hand tensioning to allow the surgeon to determine the ultimate force applied in light of the above considerations. In anticipation of future work in this area, we would emphasize that technique is critical to success, and not all tethering techniques are similar. We agree that pretensioning is critical to impart an extension moment to the spine. Dr. Buell and his colleagues should be commended for their work, and we are optimistic that ligament augmentation will play an increasingly important role in PJK/PJF prevention in surgery for adult spinal deformity.

Contributor Notes

Correspondence Thomas J. Buell: tjb4p@hscmail.mcc.virginia.edu.

INCLUDE WHEN CITING Published online August 3, 2018; DOI: 10.3171/2018.5.SPINE18636.

Disclosures Bess: research support from K2M, NuVasive, Medtronic, DePuy Synthes, ZimmerBiomet, Allosource, Orthofix, and EOS; consultant for K2M, Allosource, DePuy Synthes, Misonix, and EOS; and patent holder with K2M and Innovasis. Shaffrey: consultant for Medtronic, NuVasive, Zimmer Biomet, and K2M; and patent holder with and royalties from Medtronic, NuVasive, and Zimmer Biomet; stock holder with NuVasive. Smith: royalties from Zimmer Biomet; consultant for Zimmer Biomet, Cerapedics, NuVasive, K2M, and AlloSource; honoraria from Zimmer Biomet, NuVasive, and K2M; research support from DePuy Synthes and ISSGF; and fellowship support from NREF and AOSpine.

  • 1

    Bess S, Harris JE, Turner AW, LaFage V, Smith JS, Shaffrey CI, et al. : The effect of posterior polyester tethers on the biomechanics of proximal junctional kyphosis: a finite element analysis. J Neurosurg Spine 26:125133, 2017

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 2

    Buell TJ, Buchholz AL, Quinn JC, Bess S, Line BG, Ames CP, et al. : A pilot study on posterior polyethylene tethers to prevent proximal junctional kyphosis after multilevel spinal instrumentation for adult spinal deformity. Oper Neurosurg (Hagerstown) [epub ahead of print], 2018

    • PubMed
    • Search Google Scholar
    • Export Citation
  • 3

    Ghobrial GM, Eichberg DG, Kolcun JPG, Madhavan K, Lebwohl NH, Green BA, et al. : Prophylactic vertebral cement augmentation at the uppermost instrumented vertebra and rostral adjacent vertebra for the prevention of proximal junctional kyphosis and failure following long-segment fusion for adult spinal deformity. Spine J 17:14991505, 2017

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 4

    Safaee MM, Deviren V, Dalle Ore C, Scheer JK, Lau D, Osorio JA, et al. : Ligament augmentation for prevention of proximal junctional kyphosis and proximal junctional failure in adult spinal deformity. J Neurosurg Spine 28:512519, 2018

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation
  • 5

    Thawrani DP, Glos DL, Coombs MT, Bylski-Austrow DI, Sturm PF: Transverse process hooks at upper instrumented vertebra provide more gradual motion transition than pedicle screws. Spine (Phila Pa 1976) 39:E826832, 2014

    • Crossref
    • PubMed
    • Search Google Scholar
    • Export Citation

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